QString Class Reference
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class | Null |
typedef | ConstIterator |
typedef | Iterator |
enum | NormalizationForm { NormalizationForm_D, NormalizationForm_C, NormalizationForm_KD, NormalizationForm_KC } |
enum | SectionFlag { SectionDefault, SectionSkipEmpty, SectionIncludeLeadingSep, SectionIncludeTrailingSep, SectionCaseInsensitiveSeps } |
flags | SectionFlags |
enum | SplitBehavior { KeepEmptyParts, SkipEmptyParts } |
typedef | const_iterator |
typedef | iterator |
QString () | |
QString ( const QChar * unicode, int size ) | |
QString ( QChar ch ) | |
QString ( int size, QChar ch ) | |
QString ( const QLatin1String & str ) | |
QString ( const QString & other ) | |
QString ( const char * str ) | |
QString ( const QByteArray & ba ) | |
~QString () | |
QString & | append ( const QString & str ) |
QString & | append ( const QStringRef & reference ) |
QString & | append ( const QLatin1String & str ) |
QString & | append ( const QByteArray & ba ) |
QString & | append ( const char * str ) |
QString & | append ( QChar ch ) |
QString | arg ( const QString & a, int fieldWidth = 0, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( const QString & a1, const QString & a2 ) const |
QString | arg ( const QString & a1, const QString & a2, const QString & a3 ) const |
QString | arg ( const QString & a1, const QString & a2, const QString & a3, const QString & a4 ) const |
QString | arg ( const QString & a1, const QString & a2, const QString & a3, const QString & a4, const QString & a5 ) const |
QString | arg ( const QString & a1, const QString & a2, const QString & a3, const QString & a4, const QString & a5, const QString & a6 ) const |
QString | arg ( const QString & a1, const QString & a2, const QString & a3, const QString & a4, const QString & a5, const QString & a6, const QString & a7 ) const |
QString | arg ( const QString & a1, const QString & a2, const QString & a3, const QString & a4, const QString & a5, const QString & a6, const QString & a7, const QString & a8 ) const |
QString | arg ( const QString & a1, const QString & a2, const QString & a3, const QString & a4, const QString & a5, const QString & a6, const QString & a7, const QString & a8, const QString & a9 ) const |
QString | arg ( int a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( uint a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( long a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( ulong a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( qlonglong a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( qulonglong a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( short a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( ushort a, int fieldWidth = 0, int base = 10, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( QChar a, int fieldWidth = 0, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( char a, int fieldWidth = 0, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
QString | arg ( double a, int fieldWidth = 0, char format = 'g', int precision = -1, const QChar & fillChar = QLatin1Char( ' ' ) ) const |
const QChar | at ( int position ) const |
iterator | begin () |
const_iterator | begin () const |
int | capacity () const |
void | chop ( int n ) |
void | clear () |
int | compare ( const QString & other ) const |
int | compare ( const QString & other, Qt::CaseSensitivity cs ) const |
int | compare ( const QLatin1String & other, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | compare ( const QStringRef & ref, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
const_iterator | constBegin () const |
const QChar * | constData () const |
const_iterator | constEnd () const |
bool | contains ( const QString & str, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
bool | contains ( QChar ch, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
bool | contains ( const QRegExp & rx ) const |
bool | contains ( QRegExp & rx ) const |
int | count ( const QString & str, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | count ( QChar ch, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | count ( const QRegExp & rx ) const |
int | count () const |
QChar * | data () |
const QChar * | data () const |
iterator | end () |
const_iterator | end () const |
bool | endsWith ( const QString & s, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
bool | endsWith ( const QLatin1String & s, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
bool | endsWith ( const QChar & c, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
QString & | fill ( QChar ch, int size = -1 ) |
int | indexOf ( const QString & str, int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | indexOf ( const QLatin1String & str, int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | indexOf ( QChar ch, int from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | indexOf ( const QRegExp & rx, int from = 0 ) const |
int | indexOf ( QRegExp & rx, int from = 0 ) const |
QString & | insert ( int position, const QString & str ) |
QString & | insert ( int position, const QLatin1String & str ) |
QString & | insert ( int position, const QChar * unicode, int size ) |
QString & | insert ( int position, QChar ch ) |
bool | isEmpty () const |
bool | isNull () const |
int | lastIndexOf ( const QString & str, int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | lastIndexOf ( const QLatin1String & str, int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | lastIndexOf ( QChar ch, int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
int | lastIndexOf ( const QRegExp & rx, int from = -1 ) const |
int | lastIndexOf ( QRegExp & rx, int from = -1 ) const |
QString | left ( int n ) const |
QString | leftJustified ( int width, QChar fill = QLatin1Char( ' ' ), bool truncate = false ) const |
QStringRef | leftRef ( int n ) const |
int | length () const |
int | localeAwareCompare ( const QStringRef & other ) const |
int | localeAwareCompare ( const QString & other ) const |
QString | mid ( int position, int n = -1 ) const |
QStringRef | midRef ( int position, int n = -1 ) const |
QString | normalized ( NormalizationForm mode ) const |
QString | normalized ( NormalizationForm mode, QChar::UnicodeVersion version ) const |
QString & | prepend ( const QString & str ) |
QString & | prepend ( const QLatin1String & str ) |
QString & | prepend ( const QByteArray & ba ) |
QString & | prepend ( const char * str ) |
QString & | prepend ( QChar ch ) |
void | push_back ( const QString & other ) |
void | push_back ( QChar ch ) |
void | push_front ( const QString & other ) |
void | push_front ( QChar ch ) |
QString & | remove ( int position, int n ) |
QString & | remove ( QChar ch, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | remove ( const QString & str, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | remove ( const QRegExp & rx ) |
QString | repeated ( int times ) const |
QString & | replace ( int position, int n, const QString & after ) |
QString & | replace ( int position, int n, const QChar * unicode, int size ) |
QString & | replace ( int position, int n, QChar after ) |
QString & | replace ( const QString & before, const QString & after, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( const QChar * before, int blen, const QChar * after, int alen, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( QChar ch, const QString & after, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( QChar before, QChar after, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( const QLatin1String & before, const QLatin1String & after, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( const QLatin1String & before, const QString & after, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( const QString & before, const QLatin1String & after, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( QChar c, const QLatin1String & after, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString & | replace ( const QRegExp & rx, const QString & after ) |
void | reserve ( int size ) |
void | resize ( int size ) |
QString | right ( int n ) const |
QString | rightJustified ( int width, QChar fill = QLatin1Char( ' ' ), bool truncate = false ) const |
QStringRef | rightRef ( int n ) const |
QString | section ( QChar sep, int start, int end = -1, SectionFlags flags = SectionDefault ) const |
QString | section ( const QString & sep, int start, int end = -1, SectionFlags flags = SectionDefault ) const |
QString | section ( const QRegExp & reg, int start, int end = -1, SectionFlags flags = SectionDefault ) const |
QString & | setNum ( int n, int base = 10 ) |
QString & | setNum ( uint n, int base = 10 ) |
QString & | setNum ( long n, int base = 10 ) |
QString & | setNum ( ulong n, int base = 10 ) |
QString & | setNum ( qlonglong n, int base = 10 ) |
QString & | setNum ( qulonglong n, int base = 10 ) |
QString & | setNum ( short n, int base = 10 ) |
QString & | setNum ( ushort n, int base = 10 ) |
QString & | setNum ( double n, char format = 'g', int precision = 6 ) |
QString & | setNum ( float n, char format = 'g', int precision = 6 ) |
QString & | setUnicode ( const QChar * unicode, int size ) |
QString & | setUtf16 ( const ushort * unicode, int size ) |
QString | simplified () const |
int | size () const |
QStringList | split ( const QString & sep, SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
QStringList | split ( const QChar & sep, SplitBehavior behavior = KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
QStringList | split ( const QRegExp & rx, SplitBehavior behavior = KeepEmptyParts ) const |
QString & | sprintf ( const char * cformat, ... ) |
void | squeeze () |
bool | startsWith ( const QString & s, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
bool | startsWith ( const QLatin1String & s, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
bool | startsWith ( const QChar & c, Qt::CaseSensitivity cs = Qt::CaseSensitive ) const |
QByteArray | toAscii () const |
QString | toCaseFolded () const |
double | toDouble ( bool * ok = 0 ) const |
float | toFloat ( bool * ok = 0 ) const |
int | toInt ( bool * ok = 0, int base = 10 ) const |
QByteArray | toLatin1 () const |
QByteArray | toLocal8Bit () const |
long | toLong ( bool * ok = 0, int base = 10 ) const |
qlonglong | toLongLong ( bool * ok = 0, int base = 10 ) const |
QString | toLower () const |
short | toShort ( bool * ok = 0, int base = 10 ) const |
std::string | toStdString () const |
std::wstring | toStdWString () const |
uint | toUInt ( bool * ok = 0, int base = 10 ) const |
ulong | toULong ( bool * ok = 0, int base = 10 ) const |
qulonglong | toULongLong ( bool * ok = 0, int base = 10 ) const |
ushort | toUShort ( bool * ok = 0, int base = 10 ) const |
QVector<uint> | toUcs4 () const |
QString | toUpper () const |
QByteArray | toUtf8 () const |
int | toWCharArray ( wchar_t * array ) const |
QString | trimmed () const |
void | truncate ( int position ) |
const QChar * | unicode () const |
const ushort * | utf16 () const |
QString & | vsprintf ( const char * cformat, va_list ap ) |
bool | operator!= ( const QString & other ) const |
bool | operator!= ( const QLatin1String & other ) const |
bool | operator!= ( const QByteArray & other ) const |
bool | operator!= ( const char * other ) const |
QString & | operator+= ( const QString & other ) |
QString & | operator+= ( const QLatin1String & str ) |
QString & | operator+= ( const QByteArray & ba ) |
QString & | operator+= ( const char * str ) |
QString & | operator+= ( const QStringRef & str ) |
QString & | operator+= ( char ch ) |
QString & | operator+= ( QChar ch ) |
bool | operator< ( const QString & other ) const |
bool | operator< ( const QLatin1String & other ) const |
bool | operator< ( const QByteArray & other ) const |
bool | operator< ( const char * other ) const |
bool | operator<= ( const QString & other ) const |
bool | operator<= ( const QLatin1String & other ) const |
bool | operator<= ( const QByteArray & other ) const |
bool | operator<= ( const char * other ) const |
QString & | operator= ( const QString & other ) |
QString & | operator= ( const QLatin1String & str ) |
QString & | operator= ( const QByteArray & ba ) |
QString & | operator= ( const char * str ) |
QString & | operator= ( char ch ) |
QString & | operator= ( QChar ch ) |
bool | operator== ( const QString & other ) const |
bool | operator== ( const QLatin1String & other ) const |
bool | operator== ( const QByteArray & other ) const |
bool | operator== ( const char * other ) const |
bool | operator> ( const QString & other ) const |
bool | operator> ( const QLatin1String & other ) const |
bool | operator> ( const QByteArray & other ) const |
bool | operator> ( const char * other ) const |
bool | operator>= ( const QString & other ) const |
bool | operator>= ( const QLatin1String & other ) const |
bool | operator>= ( const QByteArray & other ) const |
bool | operator>= ( const char * other ) const |
QCharRef | operator[] ( int position ) |
const QChar | operator[] ( int position ) const |
QCharRef | operator[] ( uint position ) |
const QChar | operator[] ( uint position ) const |
int | compare ( const QString & s1, const QString & s2, Qt::CaseSensitivity cs ) |
int | compare ( const QString & s1, const QString & s2 ) |
int | compare ( const QString & s1, const QLatin1String & s2, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
int | compare ( const QLatin1String & s1, const QString & s2, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
int | compare ( const QString & s1, const QStringRef & s2, Qt::CaseSensitivity cs = Qt::CaseSensitive ) |
QString | fromAscii ( const char * str, int size = -1 ) |
QString | fromLatin1 ( const char * str, int size = -1 ) |
QString | fromLocal8Bit ( const char * str, int size = -1 ) |
QString | fromRawData ( const QChar * unicode, int size ) |
QString | fromStdString ( const std::string & str ) |
QString | fromStdWString ( const std::wstring & str ) |
QString | fromUcs4 ( const uint * unicode, int size = -1 ) |
QString | fromUtf8 ( const char * str, int size = -1 ) |
QString | fromUtf16 ( const ushort * unicode, int size = -1 ) |
QString | fromWCharArray ( const wchar_t * string, int size = -1 ) |
int | localeAwareCompare ( const QString & s1, const QString & s2 ) |
int | localeAwareCompare ( const QString & s1, const QStringRef & s2 ) |
QString | number ( long n, int base = 10 ) |
QString | number ( double n, char format = 'g', int precision = 6 ) |
QString | number ( ulong n, int base = 10 ) |
QString | number ( int n, int base = 10 ) |
QString | number ( uint n, int base = 10 ) |
QString | number ( qlonglong n, int base = 10 ) |
QString | number ( qulonglong n, int base = 10 ) |
bool | operator!= ( const char * s1, const QString & s2 ) |
const QString | operator+ ( const QString & s1, const QString & s2 ) |
const QString | operator+ ( const QString & s1, const char * s2 ) |
const QString | operator+ ( const char * s1, const QString & s2 ) |
const QString | operator+ ( char ch, const QString & s ) |
const QString | operator+ ( const QString & s, char ch ) |
bool | operator< ( const char * s1, const QString & s2 ) |
QDataStream & | operator<< ( QDataStream & stream, const QString & string ) |
bool | operator<= ( const char * s1, const QString & s2 ) |
bool | operator== ( const char * s1, const QString & s2 ) |
bool | operator> ( const char * s1, const QString & s2 ) |
bool | operator>= ( const char * s1, const QString & s2 ) |
QDataStream & | operator>> ( QDataStream & stream, QString & string ) |
QT_NO_CAST_FROM_ASCII | |
QT_NO_CAST_TO_ASCII |
The QString class provides a Unicode character string.
QString stores a string of 16-bit QChars, where each QChar corresponds one Unicode 4.0 character. (Unicode characters with code values above 65535 are stored using surrogate pairs, i.e., two consecutive QChars.)
Unicode is an international standard that supports most of the writing systems in use today. It is a superset of ASCII and Latin-1 (ISO 8859-1), and all the ASCII/Latin-1 characters are available at the same code positions.
Behind the scenes, QString uses implicit sharing (copy-on-write) to reduce memory usage and to avoid the needless copying of data. This also helps reduce the inherent overhead of storing 16-bit characters instead of 8-bit characters.
In addition to QString, Qt also provides the QByteArray class to store raw bytes and traditional 8-bit '\0'-terminated strings. For most purposes, QString is the class you want to use. It is used throughout the Qt API, and the Unicode support ensures that your applications will be easy to translate if you want to expand your application's market at some point. The two main cases where QByteArray is appropriate are when you need to store raw binary data, and when memory conservation is critical (e.g., with Qt for Embedded Linux).
One way to initialize a QString is simply to pass a const char * to its constructor. For example, the following code creates a QString of size 5 containing the data "Hello":
QString str = "Hello";
QString converts the const char * data into Unicode using the fromAscii() function. By default, fromAscii() treats character above 128 as Latin-1 characters, but this can be changed by calling QTextCodec::setCodecForCStrings().
In all of the QString functions that take const char * parameters, the const char * is interpreted as a classic C-style '\0'-terminated string. It is legal for the const char * parameter to be 0.
You can also provide string data as an array of QChars:
static const QChar data[4] = { 0x0055, 0x006e, 0x10e3, 0x03a3 }; QString str(data, 4);
QString makes a deep copy of the QChar data, so you can modify it later without experiencing side effects. (If for performance reasons you don't want to take a deep copy of the character data, use QString::fromRawData() instead.)
Another approach is to set the size of the string using resize() and to initialize the data character per character. QString uses 0-based indexes, just like C++ arrays. To access the character at a particular index position, you can use operator[](). On non-const strings, operator[]() returns a reference to a character that can be used on the left side of an assignment. For example:
QString str; str.resize(4); str[0] = QChar('U'); str[1] = QChar('n'); str[2] = QChar(0x10e3); str[3] = QChar(0x03a3);
For read-only access, an alternative syntax is to use the at() function:
QString str; for (int i = 0; i < str.size(); ++i) { if (str.at(i) >= QChar('a') && str.at(i) <= QChar('f')) qDebug() << "Found character in range [a-f]"; }
The at() function can be faster than operator[](), because it never causes a deep copy to occur. Alternatively, use the left(), right(), or mid() functions to extract several characters at a time.
A QString can embed '\0' characters (QChar::Null). The size() function always returns the size of the whole string, including embedded '\0' characters.
After a call to the resize() function, newly allocated characters have undefined values. To set all the characters in the string to a particular value, use the fill() function.
QString provides dozens of overloads designed to simplify string usage. For example, if you want to compare a QString with a string literal, you can write code like this and it will work as expected:
QString str;
if (str == "auto" || str == "extern"
|| str == "static" || str == "register") {
// ...
}
You can also pass string literals to functions that take QStrings as arguments, invoking the QString(const char *) constructor. Similarly, you can pass a QString to a function that takes a const char * argument using the qPrintable() macro which returns the given QString as a const char *. This is equivalent to calling <QString>.toLocal8Bit().constData().
QString provides the following basic functions for modifying the character data: append(), prepend(), insert(), replace(), and remove(). For example:
QString str = "and"; str.prepend("rock "); // str == "rock and" str.append(" roll"); // str == "rock and roll" str.replace(5, 3, "&"); // str == "rock & roll"
If you are building a QString gradually and know in advance approximately how many characters the QString will contain, you can call reserve(), asking QString to preallocate a certain amount of memory. You can also call capacity() to find out how much memory QString actually allocated.
The replace() and remove() functions' first two arguments are the position from which to start erasing and the number of characters that should be erased. If you want to replace all occurrences of a particular substring with another, use one of the two-parameter replace() overloads.
A frequent requirement is to remove whitespace characters from a string ('\n', '\t', ' ', etc.). If you want to remove whitespace from both ends of a QString, use the trimmed() function. If you want to remove whitespace from both ends and replace multiple consecutive whitespaces with a single space character within the string, use simplified().
If you want to find all occurrences of a particular character or substring in a QString, use the indexOf() or lastIndexOf() functions. The former searches forward starting from a given index position, the latter searches backward. Both return the index position of the character or substring if they find it; otherwise, they return -1. For example, here's a typical loop that finds all occurrences of a particular substring:
QString str = "We must be <b>bold</b>, very <b>bold</b>"; int j = 0; while ((j = str.indexOf("<b>", j)) != -1) { qDebug() << "Found <b> tag at index position" << j; ++j; }
QString provides many functions for converting numbers into strings and strings into numbers. See the arg() functions, the setNum() functions, the number() static functions, and the toInt(), toDouble(), and similar functions.
To get an upper- or lowercase version of a string use toUpper() or toLower().
Lists of strings are handled by the QStringList class. You can split a string into a list of strings using the split() function, and join a list of strings into a single string with an optional separator using QStringList::join(). You can obtain a list of strings from a string list that contain a particular substring or that match a particular QRegExp using the QStringList::find() function. :
If you want to see if a QString starts or ends with a particular substring use startsWith() or endsWith(). If you simply want to check whether a QString contains a particular character or substring, use the contains() function. If you want to find out how many times a particular character or substring occurs in the string, use count().
QStrings can be compared using overloaded operators such as operator<(), operator<=(), operator==(), operator>=(), and so on. Note that the comparison is based exclusively on the numeric Unicode values of the characters. It is very fast, but is not what a human would expect; the QString::localeAwareCompare() function is a better choice for sorting user-interface strings.
To obtain a pointer to the actual character data, call data() or constData(). These functions return a pointer to the beginning of the QChar data. The pointer is guaranteed to remain valid until a non-const function is called on the QString.
QString provides the following four functions that return a const char * version of the string as QByteArray: toAscii(), toLatin1(), toUtf8(), and toLocal8Bit().
To convert from one of these encodings, QString provides fromAscii(), fromLatin1(), fromUtf8(), and fromLocal8Bit(). Other encodings are supported through the QTextCodec class.
As mentioned above, QString provides a lot of functions and operators that make it easy to interoperate with const char * strings. But this functionality is a double-edged sword: It makes QString more convenient to use if all strings are ASCII or Latin-1, but there is always the risk that an implicit conversion from or to const char * is done using the wrong 8-bit encoding. To minimize these risks, you can turn off these implicit conversions by defining the following two preprocessor symbols:
One way to define these preprocessor symbols globally for your application is to add the following entry to your qmake project file:
DEFINES += QT_NO_CAST_FROM_ASCII \ QT_NO_CAST_TO_ASCII
You then need to explicitly call fromAscii(), fromLatin1(), fromUtf8(), or fromLocal8Bit() to construct a QString from an 8-bit string, or use the lightweight QLatin1String class, for example:
QString url = QLatin1String("http://www.unicode.org/");
Similarly, you must call toAscii(), toLatin1(), toUtf8(), or toLocal8Bit() explicitly to convert the QString to an 8-bit string. (Other encodings are supported through the QTextCodec class.)
Note for C ProgrammersDue to C++'s type system and the fact that QString is implicitly shared, QStrings may be treated like ints or other basic types. For example: QString Widget::boolToString(bool b) { QString result; if (b) result = "True"; else result = "False"; return result; } The result variable, is a normal variable allocated on the stack. When return is called, and because we're returning by value, the copy constructor is called and a copy of the string is returned. No actual copying takes place thanks to the implicit sharing. |
For historical reasons, QString distinguishes between a null string and an empty string. A null string is a string that is initialized using QString's default constructor or by passing (const char *)0 to the constructor. An empty string is any string with size 0. A null string is always empty, but an empty string isn't necessarily null:
QString().isNull(); // returns true QString().isEmpty(); // returns true QString("").isNull(); // returns false QString("").isEmpty(); // returns true QString("abc").isNull(); // returns false QString("abc").isEmpty(); // returns false
All functions except isNull() treat null strings the same as empty strings. For example, toAscii().constData() returns a pointer to a '\0' character for a null string (not a null pointer), and QString() compares equal to QString(""). We recommend that you always use the isEmpty() function and avoid isNull().
In member functions where an argument format can be specified (e.g., arg(), number()), the argument format can be one of the following:
Format | Meaning |
---|---|
e | format as [-]9.9e[+|-]999 |
E | format as [-]9.9E[+|-]999 |
f | format as [-]9.9 |
g | use e or f format, whichever is the most concise |
G | use E or f format, whichever is the most concise |
A precision is also specified with the argument format. For the 'e', 'E', and 'f' formats, the precision represents the number of digits after the decimal point. For the 'g' and 'G' formats, the precision represents the maximum number of significant digits (trailing zeroes are omitted).
Using the QString '+' operator, it is easy to construct a complex string from multiple substrings. You will often write code like this:
QString foo; QString type = "long"; foo->setText(QLatin1String("vector<") + type + QLatin1String(">::iterator")); if (foo.startsWith("(" + type + ") 0x")) ...
There is nothing wrong with either of these string constructions, but there are a few hidden inefficiencies. Beginning with Qt 4.6, you can eliminate them.
First, multiple uses of the '+' operator usually means multiple memory allocations. When concatenating n substrings, where n > 2, there can be as many as n - 1 calls to the memory allocator.
Second, QLatin1String does not store its length internally but calls qstrlen() when it needs to know its length.
In 4.6, an internal template class QStringBuilder has been added along with a few helper functions. This class is marked internal and does not appear in the documentation, because you aren't meant to instantiate it in your code. Its use will be automatic, as described below. The class is found in src/corelib/tools/qstringbuilder.cpp if you want to have a look at it.
QStringBuilder uses expression templates and reimplements the '%' operator so that when you use '%' for string concatenation instead of '+', multiple substring concatenations will be postponed until the final result is about to be assigned to a QString. At this point, the amount of memory required for the final result is known. The memory allocator is then called once to get the required space, and the substrings are copied into it one by one.
QLatin1Literal is a second internal class that can replace QLatin1String, which can't be changed for compatibility reasons. QLatin1Literal stores its length, thereby saving time when QStringBuilder computes the amount of memory required for the final string.
Additional efficiency is gained by inlining and reduced reference counting (the QString created from a QStringBuilder typically has a ref count of 1, whereas QString::append() needs an extra test).
There are three ways you can access this improved method of string construction. The straightforward way is to include QStringBuilder wherever you want to use it, and use the '%' operator instead of '+' when concatenating strings:
#include <QStringBuilder> QString hello("hello"); QStringRef el(&hello, 2, 3); QLatin1String world("world"); QString message = hello % el % world % QChar('!');
A more global approach is to include this define:
#define QT_USE_FAST_CONCATENATION
and use '%' instead of '+' for string concatenation everywhere. The third approach, which is the most convenient but not entirely source compatible, is to include two defines:
#define QT_USE_FAST_CONCATENATION #define QT_USE_FAST_OPERATOR_PLUS
and the '+' will automatically be performed as the QStringBuilder '%' everywhere.
See also fromRawData(), QChar, QLatin1String, QByteArray, and QStringRef.
Qt-style synonym for QString::const_iterator.
Qt-style synonym for QString::iterator.
This enum describes the various normalized forms of Unicode text.
Constant | Value | Description |
---|---|---|
QString::NormalizationForm_D | 0 | Canonical Decomposition |
QString::NormalizationForm_C | 1 | Canonical Decomposition followed by Canonical Composition |
QString::NormalizationForm_KD | 2 | Compatibility Decomposition |
QString::NormalizationForm_KC | 3 | Compatibility Decomposition followed by Canonical Composition |
See also normalized() and Unicode Standard Annex #15.
This enum specifies flags that can be used to affect various aspects of the section() function's behavior with respect to separators and empty fields.
Constant | Value | Description |
---|---|---|
QString::SectionDefault | 0x00 | Empty fields are counted, leading and trailing separators are not included, and the separator is compared case sensitively. |
QString::SectionSkipEmpty | 0x01 | Treat empty fields as if they don't exist, i.e. they are not considered as far as start and end are concerned. |
QString::SectionIncludeLeadingSep | 0x02 | Include the leading separator (if any) in the result string. |
QString::SectionIncludeTrailingSep | 0x04 | Include the trailing separator (if any) in the result string. |
QString::SectionCaseInsensitiveSeps | 0x08 | Compare the separator case-insensitively. |
The SectionFlags type is a typedef for QFlags<SectionFlag>. It stores an OR combination of SectionFlag values.
See also section().
This enum specifies how the split() function should behave with respect to empty strings.
Constant | Value | Description |
---|---|---|
QString::KeepEmptyParts | 0 | If a field is empty, keep it in the result. |
QString::SkipEmptyParts | 1 | If a field is empty, don't include it in the result. |
See also split().
The QString::const_iterator typedef provides an STL-style const iterator for QString.
See also QString::iterator.
The QString::iterator typedef provides an STL-style non-const iterator for QString.
See also QString::const_iterator.
Constructs a null string. Null strings are also empty.
See also isEmpty().
Constructs a string initialized with the first size characters of the QChar array unicode.
QString makes a deep copy of the string data. The unicode data is copied as is and the Byte Order Mark is preserved if present.
Constructs a string of size 1 containing the character ch.
Constructs a string of the given size with every character set to ch.
See also fill().
Constructs a copy of the Latin-1 string str.
See also fromLatin1().
Constructs a copy of other.
This operation takes constant time, because QString is implicitly shared. This makes returning a QString from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes linear time.
See also operator=().
Constructs a string initialized with the ASCII string str. The given const char pointer is converted to Unicode using the fromAscii() function.
You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
See also fromAscii(), fromLatin1(), fromLocal8Bit(), and fromUtf8().
Constructs a string initialized with the byte array ba. The given byte array is converted to Unicode using fromAscii(). Stops copying at the first 0 character, otherwise copies the entire byte array.
You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
See also fromAscii(), fromLatin1(), fromLocal8Bit(), and fromUtf8().
Destroys the string.
Appends the string str onto the end of this string.
Example:
QString x = "free";
QString y = "dom";
x.append(y);
// x == "freedom"
This is the same as using the insert() function:
x.insert(x.size(), y);
The append() function is typically very fast (constant time), because QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.
See also operator+=(), prepend(), and insert().
Appends the given string reference to this string and returns the result.
This function was introduced in Qt 4.4.
This function overloads append().
Appends the Latin-1 string str to this string.
This function overloads append().
Appends the byte array ba to this string. The given byte array is converted to Unicode using the fromAscii() function.
You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads append().
Appends the string str to this string. The given const char pointer is converted to Unicode using the fromAscii() function.
You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads append().
Appends the character ch to this string.
Returns a copy of this string with the lowest numbered place marker replaced by string a, i.e., %1, %2, ..., %99.
fieldWidth specifies the minimum amount of space that argument a shall occupy. If a requires less space than fieldWidth, it is padded to fieldWidth with character fillChar. A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.
This example shows how we might create a status string for reporting progress while processing a list of files:
QString i; // current file's number QString total; // number of files to process QString fileName; // current file's name QString status = QString("Processing file %1 of %2: %3") .arg(i).arg(total).arg(fileName);
First, arg(i) replaces %1. Then arg(total) replaces %2. Finally, arg(fileName) replaces %3.
One advantage of using arg() over sprintf() is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest numbered unreplaced place marker, no matter where it appears. Also, if place marker %i appears more than once in the string, the arg() replaces all of them.
If there is no unreplaced place marker remaining, a warning message is output and the result is undefined. Place marker numbers must be in the range 1 to 99.
This function overloads arg().
This is the same as str.arg(a1).arg(a2), except that the strings a1 and a2 are replaced in one pass. This can make a difference if a1 contains e.g. %1:
QString str; str = "%1 %2"; str.arg("%1f", "Hello"); // returns "%1f Hello" str.arg("%1f").arg("Hello"); // returns "Hellof %2"
This function overloads arg().
This is the same as calling str.arg(a1).arg(a2).arg(a3), except that the strings a1, a2 and a3 are replaced in one pass.
This function overloads arg().
This is the same as calling str.arg(a1).arg(a2).arg(a3).arg(a4), except that the strings a1, a2, a3 and a4 are replaced in one pass.
This function overloads arg().
This is the same as calling str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5), except that the strings a1, a2, a3, a4, and a5 are replaced in one pass.
This function overloads arg().
This is the same as calling str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6)), except that the strings a1, a2, a3, a4, a5, and a6 are replaced in one pass.
This function overloads arg().
This is the same as calling str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7), except that the strings a1, a2, a3, a4, a5, a6, and a7 are replaced in one pass.
This function overloads arg().
This is the same as calling str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7).arg(a8), except that the strings a1, a2, a3, a4, a5, a6, a7, and a8 are replaced in one pass.
This function overloads arg().
This is the same as calling str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7).arg(a8).arg(a9), except that the strings a1, a2, a3, a4, a5, a6, a7, a8, and a9 are replaced in one pass.
This function overloads arg().
The a argument is expressed in base base, which is 10 by default and must be between 2 and 36. For bases other than 10, a is treated as an unsigned integer.
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a. The conversion uses the default locale, set by QLocale::setDefault(). If no default locale was specified, the "C" locale is used. The 'L' flag is ignored if base is not 10.
QString str; str = QString("Decimal 63 is %1 in hexadecimal") .arg(63, 0, 16); // str == "Decimal 63 is 3f in hexadecimal" QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates)); str = QString("%1 %L2 %L3") .arg(12345) .arg(12345) .arg(12345, 0, 16); // str == "12345 12,345 3039"
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36.
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
The a argument is expressed in the given base, which is 10 by default and must be between 2 and 36.
The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a. The conversion uses the default locale. The default locale is determined from the system's locale settings at application startup. It can be changed using QLocale::setDefault(). The 'L' flag is ignored if base is not 10.
QString str; str = QString("Decimal 63 is %1 in hexadecimal") .arg(63, 0, 16); // str == "Decimal 63 is 3f in hexadecimal" QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates)); str = QString("%1 %L2 %L3") .arg(12345) .arg(12345) .arg(12345, 0, 16); // str == "12345 12,345 3039"
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a to a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
If fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.
This function overloads arg().
This function overloads arg().
The a argument is interpreted as a Latin-1 character.
This function overloads arg().
Argument a is formatted according to the specified format and precision. See Argument Formats for details.
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.
double d = 12.34;
QString str = QString("delta: %1").arg(d, 0, 'E', 3);
// str == "delta: 1.234E+01"
The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a. The conversion uses the default locale, set by QLocale::setDefaultLocale(). If no default locale was specified, the "C" locale is used.
If fillChar is '0' (the number 0, ASCII 48), this function will use the locale's zero to pad. For negative numbers, the zero padding will probably appear before the minus sign.
See also QLocale::toString().
Returns the character at the given index position in the string.
The position must be a valid index position in the string (i.e., 0 <= position < size()).
See also operator[]().
Returns an STL-style iterator pointing to the first character in the string.
See also constBegin() and end().
This function overloads begin().
Returns the maximum number of characters that can be stored in the string without forcing a reallocation.
The sole purpose of this function is to provide a means of fine tuning QString's memory usage. In general, you will rarely ever need to call this function. If you want to know how many characters are in the string, call size().
See also reserve() and squeeze().
Removes n characters from the end of the string.
If n is greater than size(), the result is an empty string.
Example:
QString str("LOGOUT\r\n");
str.chop(2);
// str == "LOGOUT"
If you want to remove characters from the beginning of the string, use remove() instead.
See also truncate(), resize(), and remove().
Clears the contents of the string and makes it empty.
See also resize() and isEmpty().
Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2.
If cs is Qt::CaseSensitive, the comparison is case sensitive; otherwise the comparison is case insensitive.
Case sensitive comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-visible strings with localeAwareCompare().
int x = QString::compare("aUtO", "AuTo", Qt::CaseInsensitive); // x == 0 int y = QString::compare("auto", "Car", Qt::CaseSensitive); // y > 0 int z = QString::compare("auto", "Car", Qt::CaseInsensitive); // z < 0
This function was introduced in Qt 4.2.
See also operator==(), operator<(), and operator>().
This function overloads compare().
Performs a case sensitive compare of s1 and s2.
This function overloads compare().
Performs a comparison of s1 and s2, using the case sensitivity setting cs.
This function was introduced in Qt 4.2.
This function overloads compare().
Performs a comparison of s1 and s2, using the case sensitivity setting cs.
This function was introduced in Qt 4.2.
This function overloads compare().
Lexically compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.
Equivalent to compare(*this, other).
This function overloads compare().
Same as compare(*this, other, cs).
This function was introduced in Qt 4.2.
This function overloads compare().
Same as compare(*this, other, cs).
This function was introduced in Qt 4.2.
This function overloads compare().
Compares the string reference, ref, with the string and returns an integer less than, equal to, or greater than zero if the string is less than, equal to, or greater than ref.
This function overloads compare().
Returns a const STL-style iterator pointing to the first character in the string.
See also begin() and constEnd().
Returns a pointer to the data stored in the QString. The pointer can be used to access the characters that compose the string. For convenience, the data is '\0'-terminated.
Note that the pointer remains valid only as long as the string is not modified.
See also data() and operator[]().
Returns a const STL-style iterator pointing to the imaginary item after the last item in the list.
See also constBegin() and end().
Returns true if this string contains an occurrence of the string str; otherwise returns false.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString str = "Peter Pan";
str.contains("peter", Qt::CaseInsensitive); // returns true
See also indexOf() and count().
This function overloads contains().
Returns true if this string contains an occurrence of the character ch; otherwise returns false.
This function overloads contains().
Returns true if the regular expression rx matches somewhere in this string; otherwise returns false.
This function overloads contains().
Returns true if the regular expression rx matches somewhere in this string; otherwise returns false.
If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength, QRegExp::cap).
This function was introduced in Qt 4.5.
Returns the number of (potentially overlapping) occurrences of the string str in this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
See also contains() and indexOf().
This function overloads count().
Returns the number of occurrences of character ch in the string.
This function overloads count().
Returns the number of times the regular expression rx matches in the string.
This function counts overlapping matches, so in the example below, there are four instances of "ana" or "ama":
QString str = "banana and panama";
str.count(QRegExp("a[nm]a")); // returns 4
This function overloads count().
Same as size().
Returns a pointer to the data stored in the QString. The pointer can be used to access and modify the characters that compose the string. For convenience, the data is '\0'-terminated.
Example:
QString str = "Hello world"; QChar *data = str.data(); while (!data->isNull()) { qDebug() << data->unicode(); ++data; }
Note that the pointer remains valid only as long as the string is not modified by other means. For read-only access, constData() is faster because it never causes a deep copy to occur.
See also constData() and operator[]().
This is an overloaded function.
Returns an STL-style iterator pointing to the imaginary character after the last character in the string.
See also begin() and constEnd().
This function overloads end().
Returns true if the string ends with s; otherwise returns false.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
QString str = "Bananas"; str.endsWith("anas"); // returns true str.endsWith("pple"); // returns false
See also startsWith().
This function overloads endsWith().
Returns true if the string ends with c; otherwise returns false.
This function overloads endsWith().
Sets every character in the string to character ch. If size is different from -1 (default), the string is resized to size beforehand.
Example:
QString str = "Berlin"; str.fill('z'); // str == "zzzzzz" str.fill('A', 2); // str == "AA"
See also resize().
Returns a QString initialized with the first size characters of the 8-bit ASCII string str.
If size is -1 (default), it is taken to be qstrlen(str).
If a codec has been set using QTextCodec::setCodecForCStrings(), it is used to convert str to Unicode; otherwise this function does the same as fromLatin1().
See also toAscii(), fromLatin1(), fromUtf8(), and fromLocal8Bit().
Returns a QString initialized with the first size characters of the Latin-1 string str.
If size is -1 (default), it is taken to be qstrlen(str).
See also toLatin1(), fromAscii(), fromUtf8(), and fromLocal8Bit().
Returns a QString initialized with the first size characters of the 8-bit string str.
If size is -1 (default), it is taken to be qstrlen(str).
QTextCodec::codecForLocale() is used to perform the conversion from Unicode.
See also toLocal8Bit(), fromAscii(), fromLatin1(), and fromUtf8().
Constructs a QString that uses the first size Unicode characters in the array unicode. The data in unicode is not copied. The caller must be able to guarantee that unicode will not be deleted or modified as long as the QString (or an unmodified copy of it) exists.
Any attempts to modify the QString or copies of it will cause it to create a deep copy of the data, ensuring that the raw data isn't modified.
Here's an example of how we can use a QRegExp on raw data in memory without requiring to copy the data into a QString:
QRegExp pattern;
static const QChar unicode[] = {
0x005A, 0x007F, 0x00A4, 0x0060,
0x1009, 0x0020, 0x0020};
int size = sizeof(unicode) / sizeof(QChar);
QString str = QString::fromRawData(unicode, size);
if (str.contains(QRegExp(pattern))) {
// ...
}
Warning: A string created with fromRawData() is not '\0'-terminated, unless the raw data contains a '\0' character at position size. This means unicode() will not return a '\0'-terminated string (although utf16() does, at the cost of copying the raw data).
See also fromUtf16().
Returns a copy of the str string. The given string is converted to Unicode using the fromAscii() function.
This constructor is only available if Qt is configured with STL compatibility enabled.
See also fromAscii(), fromLatin1(), fromLocal8Bit(), and fromUtf8().
Returns a copy of the str string. The given string is assumed to be encoded in utf16 if the size of wchar_t is 2 bytes (e.g. on windows) and ucs4 if the size of wchar_t is 4 bytes (most Unix systems).
This method is only available if Qt is configured with STL compatibility enabled.
See also fromUtf16(), fromLatin1(), fromLocal8Bit(), fromUtf8(), and fromUcs4().
Returns a QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UCS-4 encoded).
If size is -1 (default), unicode must be terminated with a 0.
This function was introduced in Qt 4.2.
See also toUcs4(), fromUtf16(), utf16(), setUtf16(), and fromWCharArray().
Returns a QString initialized with the first size bytes of the UTF-8 string str.
If size is -1 (default), it is taken to be qstrlen(str).
See also toUtf8(), fromAscii(), fromLatin1(), and fromLocal8Bit().
Returns a QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UTF-16 encoded).
If size is -1 (default), unicode must be terminated with a 0.
QString makes a deep copy of the Unicode data.
See also utf16() and setUtf16().
Returns a copy of the string, where the encoding of string depends on the size of wchar. If wchar is 4 bytes, the string is interpreted as ucs-4, if wchar is 2 bytes it is interpreted as ucs-2.
If size is -1 (default), the string has to be 0 terminated.
This function was introduced in Qt 4.2.
See also fromUtf16(), fromLatin1(), fromLocal8Bit(), fromUtf8(), fromUcs4(), and fromStdWString().
Returns the index position of the first occurrence of the string str in this string, searching forward from index position from. Returns -1 if str is not found.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString x = "sticky question"; QString y = "sti"; x.indexOf(y); // returns 0 x.indexOf(y, 1); // returns 10 x.indexOf(y, 10); // returns 10 x.indexOf(y, 11); // returns -1
If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
See also lastIndexOf(), contains(), and count().
Returns the index position of the first occurrence of the string str in this string, searching forward from index position from. Returns -1 if str is not found.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString x = "sticky question"; QString y = "sti"; x.indexOf(y); // returns 0 x.indexOf(y, 1); // returns 10 x.indexOf(y, 10); // returns 10 x.indexOf(y, 11); // returns -1
If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
This function was introduced in Qt 4.5.
See also lastIndexOf(), contains(), and count().
This function overloads indexOf().
Returns the index position of the first occurrence of the character ch in the string, searching forward from index position from. Returns -1 if ch could not be found.
This function overloads indexOf().
Returns the index position of the first match of the regular expression rx in the string, searching forward from index position from. Returns -1 if rx didn't match anywhere.
Example:
QString str = "the minimum";
str.indexOf(QRegExp("m[aeiou]"), 0); // returns 4
This function overloads indexOf().
Returns the index position of the first match of the regular expression rx in the string, searching forward from index position from. Returns -1 if rx didn't match anywhere.
If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength, QRegExp::cap).
Example:
QString str = "the minimum";
str.indexOf(QRegExp("m[aeiou]"), 0); // returns 4
This function was introduced in Qt 4.5.
Inserts the string str at the given index position and returns a reference to this string.
Example:
QString str = "Meal";
str.insert(1, QString("ontr"));
// str == "Montreal"
If the given position is greater than size(), the array is first extended using resize().
See also append(), prepend(), replace(), and remove().
This function overloads insert().
Inserts the Latin-1 string str at the given index position.
This function overloads insert().
Inserts the first size characters of the QChar array unicode at the given index position in the string.
This function overloads insert().
Inserts ch at the given index position in the string.
Returns true if the string has no characters; otherwise returns false.
Example:
QString().isEmpty(); // returns true QString("").isEmpty(); // returns true QString("x").isEmpty(); // returns false QString("abc").isEmpty(); // returns false
See also size().
Returns true if this string is null; otherwise returns false.
Example:
QString().isNull(); // returns true QString("").isNull(); // returns false QString("abc").isNull(); // returns false
Qt makes a distinction between null strings and empty strings for historical reasons. For most applications, what matters is whether or not a string contains any data, and this can be determined using the isEmpty() function.
See also isEmpty().
Returns the index position of the last occurrence of the string str in this string, searching backward from index position from. If from is -1 (default), the search starts at the last character; if from is -2, at the next to last character and so on. Returns -1 if str is not found.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString x = "crazy azimuths"; QString y = "az"; x.lastIndexOf(y); // returns 6 x.lastIndexOf(y, 6); // returns 6 x.lastIndexOf(y, 5); // returns 2 x.lastIndexOf(y, 1); // returns -1
See also indexOf(), contains(), and count().
Returns the index position of the last occurrence of the string str in this string, searching backward from index position from. If from is -1 (default), the search starts at the last character; if from is -2, at the next to last character and so on. Returns -1 if str is not found.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString x = "crazy azimuths"; QString y = "az"; x.lastIndexOf(y); // returns 6 x.lastIndexOf(y, 6); // returns 6 x.lastIndexOf(y, 5); // returns 2 x.lastIndexOf(y, 1); // returns -1
This function was introduced in Qt 4.5.
See also indexOf(), contains(), and count().
This function overloads lastIndexOf().
Returns the index position of the last occurrence of the character ch, searching backward from position from.
This function overloads lastIndexOf().
Returns the index position of the last match of the regular expression rx in the string, searching backward from index position from. Returns -1 if rx didn't match anywhere.
Example:
QString str = "the minimum";
str.lastIndexOf(QRegExp("m[aeiou]")); // returns 8
This function overloads lastIndexOf().
Returns the index position of the last match of the regular expression rx in the string, searching backward from index position from. Returns -1 if rx didn't match anywhere.
If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength, QRegExp::cap).
Example:
QString str = "the minimum";
str.lastIndexOf(QRegExp("m[aeiou]")); // returns 8
This function was introduced in Qt 4.5.
Returns a substring that contains the n leftmost characters of the string.
The entire string is returned if n is greater than size() or less than zero.
QString x = "Pineapple";
QString y = x.left(4); // y == "Pine"
See also right(), mid(), and startsWith().
Returns a string of size width that contains this string padded by the fill character.
If truncate is false and the size() of the string is more than width, then the returned string is a copy of the string.
QString s = "apple";
QString t = s.leftJustified(8, '.'); // t == "apple..."
If truncate is true and the size() of the string is more than width, then any characters in a copy of the string after position width are removed, and the copy is returned.
QString str = "Pineapple";
str = str.leftJustified(5, '.', true); // str == "Pinea"
See also rightJustified().
Returns a substring reference to the n leftmost characters of the string.
If n is greater than size() or less than zero, a reference to the entire string is returned.
QString x = "Pineapple";
QStringRef y = x.leftRef(4); // y == "Pine"
This function was introduced in Qt 4.4.
See also left(), rightRef(), midRef(), and startsWith().
Returns the number of characters in this string. Equivalent to size().
See also setLength().
Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2.
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
On Mac OS X since Qt 4.3, this function compares according the "Order for sorted lists" setting in the International prefereces panel.
See also compare() and QTextCodec::locale().
This function overloads localeAwareCompare().
Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
Same as localeAwareCompare(*this, other).
This function was introduced in Qt 4.5.
This function overloads localeAwareCompare().
Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2.
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
This function was introduced in Qt 4.5.
This function overloads localeAwareCompare().
Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
Same as localeAwareCompare(*this, other).
Returns a string that contains n characters of this string, starting at the specified position index.
Returns a null string if the position index exceeds the length of the string. If there are less than n characters available in the string starting at the given position, or if n is -1 (default), the function returns all characters that are available from the specified position.
Example:
QString x = "Nine pineapples"; QString y = x.mid(5, 4); // y == "pine" QString z = x.mid(5); // z == "pineapples"
Returns a substring reference to n characters of this string, starting at the specified position.
If the position exceeds the length of the string, an empty reference is returned.
If there are less than n characters available in the string, starting at the given position, or if n is -1 (default), the function returns all characters from the specified position onwards.
Example:
QString x = "Nine pineapples"; QStringRef y = x.midRef(5, 4); // y == "pine" QStringRef z = x.midRef(5); // z == "pineapples"
This function was introduced in Qt 4.4.
See also mid(), leftRef(), and rightRef().
Returns the string in the given Unicode normalization mode.
This is an overloaded function.
Returns the string in the given Unicode normalization mode, according to the given version of the Unicode standard.
Returns a string equivalent of the number n according to the specified base.
The base is 10 by default and must be between 2 and 36. For bases other than 10, n is treated as an unsigned integer.
long a = 63; QString s = QString::number(a, 16); // s == "3f" QString t = QString::number(a, 16).toUpper(); // t == "3F"
See also setNum().
Returns a string equivalent of the number n, formatted according to the specified format and precision. See Argument Formats for details.
Unlike QLocale::toString(), this function does not honor the user's locale settings.
See also setNum() and QLocale::toString().
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
Prepends the string str to the beginning of this string and returns a reference to this string.
Example:
QString x = "ship";
QString y = "air";
x.prepend(y);
// x == "airship"
See also append() and insert().
This function overloads prepend().
Prepends the Latin-1 string str to this string.
This function overloads prepend().
Prepends the byte array ba to this string. The byte array is converted to Unicode using the fromAscii() function.
You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads prepend().
Prepends the string str to this string. The const char pointer is converted to Unicode using the fromAscii() function.
You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads prepend().
Prepends the character ch to this string.
This function is provided for STL compatibility, appending the given other string onto the end of this string. It is equivalent to append(other).
See also append().
This is an overloaded function.
Appends the given ch character onto the end of this string.
This function is provided for STL compatibility, prepending the given other string to the beginning of this string. It is equivalent to prepend(other).
See also prepend().
This is an overloaded function.
Prepends the given ch character to the beginning of this string.
Removes n characters from the string, starting at the given position index, and returns a reference to the string.
If the specified position index is within the string, but position + n is beyond the end of the string, the string is truncated at the specified position.
QString s = "Montreal";
s.remove(1, 4);
// s == "Meal"
See also insert() and replace().
Removes every occurrence of the character ch in this string, and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString t = "Ali Baba";
t.remove(QChar('a'), Qt::CaseInsensitive);
// t == "li Bb"
This is the same as replace(ch, "", cs).
See also replace().
Removes every occurrence of the given str string in this string, and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
This is the same as replace(str, "", cs).
See also replace().
Removes every occurrence of the regular expression rx in the string, and returns a reference to the string. For example:
QString r = "Telephone";
r.remove(QRegExp("[aeiou]."));
// r == "The"
See also indexOf(), lastIndexOf(), and replace().
Returns a copy of this string repeated the specified number of times.
If times is less than 1, an empty string is returned.
Example:
QString str("ab");
str.repeated(4); // returns "abababab"
This function was introduced in Qt 4.5.
Replaces n characters beginning at index position with the string after and returns a reference to this string.
Example:
QString x = "Say yes!";
QString y = "no";
x.replace(4, 3, y);
// x == "Say no!"
See also insert() and remove().
This function overloads replace().
Replaces n characters beginning at index position with the first size characters of the QChar array unicode and returns a reference to this string.
This function overloads replace().
Replaces n characters beginning at index position with the character after and returns a reference to this string.
This function overloads replace().
Replaces every occurrence of the string before with the string after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString str = "colour behaviour flavour neighbour";
str.replace(QString("ou"), QString("o"));
// str == "color behavior flavor neighbor"
Note: The replacement text is not rescanned after it is inserted.
Example:
QString equis = "xxxxxx";
equis.replace("xx", "x");
// equis == "xxx"
This function overloads replace().
Replaces each occurrence in this string of the first blen characters of before with the first alen characters of after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
This function was introduced in Qt 4.5.
This function overloads replace().
Replaces every occurrence of the character ch in the string with after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
This function overloads replace().
Replaces every occurrence of the character before with the character after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
This function overloads replace().
Replaces every occurrence of the string before with the string after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Note: The text is not rescanned after a replacement.
This function was introduced in Qt 4.5.
This function overloads replace().
Replaces every occurrence of the string before with the string after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Note: The text is not rescanned after a replacement.
This function was introduced in Qt 4.5.
This function overloads replace().
Replaces every occurrence of the string before with the string after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Note: The text is not rescanned after a replacement.
This function was introduced in Qt 4.5.
This function overloads replace().
Replaces every occurrence of the character c with the string after and returns a reference to this string.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
Note: The text is not rescanned after a replacement.
This function was introduced in Qt 4.5.
This function overloads replace().
Replaces every occurrence of the regular expression rx in the string with after. Returns a reference to the string. For example:
QString s = "Banana";
s.replace(QRegExp("a[mn]"), "ox");
// s == "Boxoxa"
For regular expressions containing capturing parentheses, occurrences of \1, \2, ..., in after are replaced with rx.cap(1), cap(2), ...
QString t = "A <i>bon mot</i>.";
t.replace(QRegExp("<i>([^<]*)</i>"), "\\emph{\\1}");
// t == "A \\emph{bon mot}."
See also indexOf(), lastIndexOf(), remove(), and QRegExp::cap().
Attempts to allocate memory for at least size characters. If you know in advance how large the string will be, you can call this function, and if you resize the string often you are likely to get better performance. If size is an underestimate, the worst that will happen is that the QString will be a bit slower.
The sole purpose of this function is to provide a means of fine tuning QString's memory usage. In general, you will rarely ever need to call this function. If you want to change the size of the string, call resize().
This function is useful for code that needs to build up a long string and wants to avoid repeated reallocation. In this example, we want to add to the string until some condition is true, and we're fairly sure that size is large enough to make a call to reserve() worthwhile:
QString result; int maxSize; bool condition; QChar nextChar; result.reserve(maxSize); while (condition) result.append(nextChar); result.squeeze();
See also squeeze() and capacity().
Sets the size of the string to size characters.
If size is greater than the current size, the string is extended to make it size characters long with the extra characters added to the end. The new characters are uninitialized.
If size is less than the current size, characters are removed from the end.
Example:
QString s = "Hello world"; s.resize(5); // s == "Hello" s.resize(8); // s == "Hello???" (where ? stands for any character)
If you want to append a certain number of identical characters to the string, use operator+=() as follows rather than resize():
QString t = "Hello";
t += QString(10, 'X');
// t == "HelloXXXXXXXXXX"
If you want to expand the string so that it reaches a certain width and fill the new positions with a particular character, use the leftJustified() function:
If size is negative, it is equivalent to passing zero.
QString r = "Hello";
r = r.leftJustified(10, ' ');
// r == "Hello "
See also truncate() and reserve().
Returns a substring that contains the n rightmost characters of the string.
The entire string is returned if n is greater than size() or less than zero.
QString x = "Pineapple";
QString y = x.right(5); // y == "apple"
See also left(), mid(), and endsWith().
Returns a string of size() width that contains the fill character followed by the string. For example:
QString s = "apple";
QString t = s.rightJustified(8, '.'); // t == "...apple"
If truncate is false and the size() of the string is more than width, then the returned string is a copy of the string.
If truncate is true and the size() of the string is more than width, then the resulting string is truncated at position width.
QString str = "Pineapple";
str = str.rightJustified(5, '.', true); // str == "Pinea"
See also leftJustified().
Returns a substring reference to the n rightmost characters of the string.
If n is greater than size() or less than zero, a reference to the entire string is returned.
QString x = "Pineapple";
QStringRef y = x.rightRef(5); // y == "apple"
This function was introduced in Qt 4.4.
See also right(), leftRef(), midRef(), and endsWith().
This function returns a section of the string.
This string is treated as a sequence of fields separated by the character, sep. The returned string consists of the fields from position start to position end inclusive. If end is not specified, all fields from position start to the end of the string are included. Fields are numbered 0, 1, 2, etc., counting from the left, and -1, -2, etc., counting from right to left.
The flags argument can be used to affect some aspects of the function's behavior, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags.
QString str; QString csv = "forename,middlename,surname,phone"; QString path = "/usr/local/bin/myapp"; // First field is empty QString::SectionFlag flag = QString::SectionSkipEmpty; str = csv.section(',', 2, 2); // str == "surname" str = path.section('/', 3, 4); // str == "bin/myapp" str = path.section('/', 3, 3, flag); // str == "myapp"
If start or end is negative, we count fields from the right of the string, the right-most field being -1, the one from right-most field being -2, and so on.
str = csv.section(',', -3, -2); // str == "middlename,surname" str = path.section('/', -1); // str == "myapp"
See also split().
This function overloads section().
QString str; QString data = "forename**middlename**surname**phone"; str = data.section("**", 2, 2); // str == "surname" str = data.section("**", -3, -2); // str == "middlename**surname"
See also split().
This function overloads section().
This string is treated as a sequence of fields separated by the regular expression, reg.
QString line = "forename\tmiddlename surname \t \t phone"; QRegExp sep("\\s+"); str = line.section(sep, 2, 2); // s == "surname" str = line.section(sep, -3, -2); // s == "middlename surname"
Warning: Using this QRegExp version is much more expensive than the overloaded string and character versions.
See also split() and simplified().
Sets the string to the printed value of n in the specified base, and returns a reference to the string.
The base is 10 by default and must be between 2 and 36. For bases other than 10, n is treated as an unsigned integer.
QString str;
str.setNum(1234); // str == "1234"
The formatting always uses QLocale::C, i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString() with the appropriate locale.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
This is an overloaded function.
Sets the string to the printed value of n, formatted according to the given format and precision, and returns a reference to the string.
The format can be 'f', 'F', 'e', 'E', 'g' or 'G' (see the arg() function documentation for an explanation of the formats).
Unlike QLocale::toString(), this function doesn't honor the user's locale settings.
This is an overloaded function.
Sets the string to the printed value of n, formatted according to the given format and precision, and returns a reference to the string.
Resizes the string to size characters and copies unicode into the string.
If unicode is 0, nothing is copied, but the string is still resized to size.
See also unicode() and setUtf16().
Resizes the string to size characters and copies unicode into the string.
If unicode is 0, nothing is copied, but the string is still resized to size.
See also utf16() and setUnicode().
Returns a string that has whitespace removed from the start and the end, and that has each sequence of internal whitespace replaced with a single space.
Whitespace means any character for which QChar::isSpace() returns true. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
Example:
QString str = " lots\t of\nwhitespace\r\n ";
str = str.simplified();
// str == "lots of whitespace";
See also trimmed().
Returns the number of characters in this string.
The last character in the string is at position size() - 1. In addition, QString ensures that the character at position size() is always '\0', so that you can use the return value of data() and constData() as arguments to functions that expect '\0'-terminated strings.
Example:
QString str = "World"; int n = str.size(); // n == 5 str.data()[0]; // returns 'W' str.data()[4]; // returns 'd' str.data()[5]; // returns '\0'
See also isEmpty() and resize().
Splits the string into substrings wherever sep occurs, and returns the list of those strings. If sep does not match anywhere in the string, split() returns a single-element list containing this string.
cs specifies whether sep should be matched case sensitively or case insensitively.
If behavior is QString::SkipEmptyParts, empty entries don't appear in the result. By default, empty entries are kept.
Example:
QString str = "a,,b,c"; QStringList list1 = str.split(","); // list1: [ "a", "", "b", "c" ] QStringList list2 = str.split(",", QString::SkipEmptyParts); // list2: [ "a", "b", "c" ]
See also QStringList::join() and section().
This is an overloaded function.
This is an overloaded function.
Splits the string into substrings wherever the regular expression rx matches, and returns the list of those strings. If rx does not match anywhere in the string, split() returns a single-element list containing this string.
Here's an example where we extract the words in a sentence using one or more whitespace characters as the separator:
QString str;
QStringList list;
str = "Some text\n\twith strange whitespace.";
list = str.split(QRegExp("\\s+"));
// list: [ "Some", "text", "with", "strange", "whitespace." ]
Here's a similar example, but this time we use any sequence of non-word characters as the separator:
str = "This time, a normal English sentence.";
list = str.split(QRegExp("\\W+"), QString::SkipEmptyParts);
// list: [ "This", "time", "a", "normal", "English", "sentence" ]
Here's a third example where we use a zero-length assertion, \b (word boundary), to split the string into an alternating sequence of non-word and word tokens:
str = "Now: this sentence fragment.";
list = str.split(QRegExp("\\b"));
// list: [ "", "Now", ": ", "this", " ", "sentence", " ", "fragment", "." ]
See also QStringList::join() and section().
Safely builds a formatted string from the format string cformat and an arbitrary list of arguments.
The %lc escape sequence expects a unicode character of type ushort (as returned by QChar::unicode()). The %ls escape sequence expects a pointer to a zero-terminated array of unicode characters of type ushort (as returned by QString::utf16()).
Note: This function expects a UTF-8 string for %s and Latin-1 for the format string.
The format string supports most of the conversion specifiers provided by printf() in the standard C++ library. It doesn't honor the length modifiers (e.g. h for short, ll for long long). If you need those, use the standard snprintf() function instead:
size_t BufSize; char buf[BufSize]; ::snprintf(buf, BufSize, "%lld", 123456789LL); QString str = QString::fromAscii(buf);
Warning: We do not recommend using QString::sprintf() in new Qt code. Instead, consider using QTextStream or arg(), both of which support Unicode strings seamlessly and are type-safe. Here's an example that uses QTextStream:
QString result;
QTextStream(&result) << "pi = " << 3.14;
// result == "pi = 3.14"
For translations, especially if the strings contains more than one escape sequence, you should consider using the arg() function instead. This allows the order of the replacements to be controlled by the translator.
See also arg().
Releases any memory not required to store the character data.
The sole purpose of this function is to provide a means of fine tuning QString's memory usage. In general, you will rarely ever need to call this function.
See also reserve() and capacity().
Returns true if the string starts with s; otherwise returns false.
If cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.
QString str = "Bananas"; str.startsWith("Ban"); // returns true str.startsWith("Car"); // returns false
See also endsWith().
This function overloads startsWith().
This function overloads startsWith().
Returns true if the string starts with c; otherwise returns false.
Returns an 8-bit ASCII representation of the string as a QByteArray.
If a codec has been set using QTextCodec::setCodecForCStrings(), it is used to convert Unicode to 8-bit char; otherwise this function does the same as toLatin1().
See also fromAscii(), toLatin1(), toUtf8(), toLocal8Bit(), and QTextCodec.
Returns the case folded equivalent of the string. For most Unicode characters this is the same as toLower().
Returns the string converted to a double value.
Returns 0.0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
QString str = "1234.56";
double val = str.toDouble(); // val == 1234.56
Various string formats for floating point numbers can be converted to double values:
bool ok;
double d;
d = QString( "1234.56e-02" ).toDouble(&ok); // ok == true, d == 12.3456
This function tries to interpret the string according to the current locale. The current locale is determined from the system at application startup and can be changed by calling QLocale::setDefault(). If the string cannot be interpreted according to the current locale, this function falls back on the "C" locale.
QLocale::setDefault(QLocale::C); d = QString( "1234,56" ).toDouble(&ok); // ok == false d = QString( "1234.56" ).toDouble(&ok); // ok == true, d == 1234.56 QLocale::setDefault(QLocale::German); d = QString( "1234,56" ).toDouble(&ok); // ok == true, d == 1234.56 d = QString( "1234.56" ).toDouble(&ok); // ok == true, d == 1234.56
Due to the ambiguity between the decimal point and thousands group separator in various locales, this function does not handle thousands group separators. If you need to convert such numbers, see QLocale::toDouble().
QLocale::setDefault(QLocale::C);
d = QString( "1234,56" ).toDouble(&ok); // ok == false
See also number(), QLocale::setDefault(), QLocale::toDouble(), and trimmed().
Returns the string converted to a float value.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true. Returns 0.0 if the conversion fails.
Example:
QString str1 = "1234.56"; str1.toFloat(); // returns 1234.56 bool ok; QString str2 = "R2D2"; str2.toFloat(&ok); // returns 0.0, sets ok to false
See also number(), toDouble(), and toInt().
Returns the string converted to an int using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; int hex = str.toInt(&ok, 16); // hex == 255, ok == true int dec = str.toInt(&ok, 10); // dec == 0, ok == false
See also number(), toUInt(), and toDouble().
Returns a Latin-1 representation of the string as a QByteArray. The returned byte array is undefined if the string contains non-Latin1 characters.
See also fromLatin1(), toAscii(), toUtf8(), toLocal8Bit(), and QTextCodec.
Returns the local 8-bit representation of the string as a QByteArray. The returned byte array is undefined if the string contains characters not supported by the local 8-bit encoding.
QTextCodec::codecForLocale() is used to perform the conversion from Unicode.
See also fromLocal8Bit(), toAscii(), toLatin1(), toUtf8(), and QTextCodec.
Returns the string converted to a long using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; long hex = str.toLong(&ok, 16); // hex == 255, ok == true long dec = str.toLong(&ok, 10); // dec == 0, ok == false
See also number(), toULong(), and toInt().
Returns the string converted to a long long using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; qint64 hex = str.toLongLong(&ok, 16); // hex == 255, ok == true qint64 dec = str.toLongLong(&ok, 10); // dec == 0, ok == false
See also number(), toULongLong(), and toInt().
Returns a lowercase copy of the string.
QString str = "Qt by NOKIA";
str = str.toLower(); // str == "qy by nokia"
See also toUpper().
Returns the string converted to a short using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; short hex = str.toShort(&ok, 16); // hex == 255, ok == true short dec = str.toShort(&ok, 10); // dec == 0, ok == false
See also number(), toUShort(), and toInt().
Returns a std::string object with the data contained in this QString. The Unicode data is converted into 8-bit characters using the toAscii() function.
This operator is mostly useful to pass a QString to a function that accepts a std::string object.
If the QString contains non-ASCII Unicode characters, using this operator can lead to loss of information, since the implementation calls toAscii().
This operator is only available if Qt is configured with STL compatibility enabled.
See also toAscii(), toLatin1(), toUtf8(), and toLocal8Bit().
Returns a std::wstring object with the data contained in this QString. The std::wstring is encoded in utf16 on platforms where wchar_t is 2 bytes wide (e.g. windows) and in ucs4 on platforms where wchar_t is 4 bytes wide (most Unix systems).
This operator is mostly useful to pass a QString to a function that accepts a std::wstring object.
This operator is only available if Qt is configured with STL compatibility enabled.
See also utf16(), toAscii(), toLatin1(), toUtf8(), and toLocal8Bit().
Returns the string converted to an unsigned int using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; uint hex = str.toUInt(&ok, 16); // hex == 255, ok == true uint dec = str.toUInt(&ok, 10); // dec == 0, ok == false
See also number() and toInt().
Returns the string converted to an unsigned long using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; ulong hex = str.toULong(&ok, 16); // hex == 255, ok == true ulong dec = str.toULong(&ok, 10); // dec == 0, ok == false
See also number().
Returns the string converted to an unsigned long long using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; quint64 hex = str.toULongLong(&ok, 16); // hex == 255, ok == true quint64 dec = str.toULongLong(&ok, 10); // dec == 0, ok == false
See also number() and toLongLong().
Returns the string converted to an unsigned short using base base, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
If a conversion error occurs, *ok is set to false; otherwise *ok is set to true.
If base is 0, the C language convention is used: If the string begins with "0x", base 16 is used; if the string begins with "0", base 8 is used; otherwise, base 10 is used.
Example:
QString str = "FF"; bool ok; ushort hex = str.toUShort(&ok, 16); // hex == 255, ok == true ushort dec = str.toUShort(&ok, 10); // dec == 0, ok == false
See also number() and toShort().
Returns a UCS-4 representation of the string as a QVector<uint>.
This function was introduced in Qt 4.2.
See also fromUtf8(), toAscii(), toLatin1(), toLocal8Bit(), QTextCodec, fromUcs4(), and toWCharArray().
Returns an uppercase copy of the string.
QString str = "TeXt";
str = str.toUpper(); // str == "TEXT"
See also toLower().
Returns a UTF-8 representation of the string as a QByteArray.
See also fromUtf8(), toAscii(), toLatin1(), toLocal8Bit(), and QTextCodec.
Fills the array with the data contained in this QString object. The array is encoded in utf16 on platforms where wchar_t is 2 bytes wide (e.g. windows) and in ucs4 on platforms where wchar_t is 4 bytes wide (most Unix systems).
array has to be allocated by the caller and contain enough space to hold the complete string (allocating the array with the same length as the string is always sufficient).
returns the actual length of the string in array.
Note: This function does not append a null character to the array.
This function was introduced in Qt 4.2.
See also utf16(), toUcs4(), toAscii(), toLatin1(), toUtf8(), toLocal8Bit(), and toStdWString().
Returns a string that has whitespace removed from the start and the end.
Whitespace means any character for which QChar::isSpace() returns true. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
Example:
QString str = " lots\t of\nwhitespace\r\n ";
str = str.trimmed();
// str == "lots\t of\nwhitespace"
Unlike simplified(), trimmed() leaves internal whitespace alone.
See also simplified().
Truncates the string at the given position index.
If the specified position index is beyond the end of the string, nothing happens.
Example:
QString str = "Vladivostok";
str.truncate(4);
// str == "Vlad"
If position is negative, it is equivalent to passing zero.
See also chop(), resize(), and left().
Returns a '\0'-terminated Unicode representation of the string. The result remains valid until the string is modified.
See also setUnicode() and utf16().
Returns the QString as a '\0'-terminated array of unsigned shorts. The result remains valid until the string is modified.
See also setUtf16() and unicode().
Equivalent method to sprintf(), but takes a va_list ap instead a list of variable arguments. See the sprintf() documentation for an explanation of cformat.
This method does not call the va_end macro, the caller is responsible to call va_end on ap.
See also sprintf().
Returns true if this string is not equal to string other; otherwise returns false.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().
This function overloads operator!=().
This function overloads operator!=().
The other byte array is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator!=().
The other const char pointer is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
Appends the string other onto the end of this string and returns a reference to this string.
Example:
QString x = "free";
QString y = "dom";
x += y;
// x == "freedom"
This operation is typically very fast (constant time), because QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.
See also append() and prepend().
This function overloads operator+=().
Appends the Latin-1 string str to this string.
This function overloads operator+=().
Appends the byte array ba to this string. The byte array is converted to Unicode using the fromAscii() function.
You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator+=().
Appends the string str to this string. The const char pointer is converted to Unicode using the fromAscii() function.
You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator+=().
Appends the string section referenced by str to this string.
This function overloads operator+=().
Appends the character ch to this string. The character is converted to Unicode using the fromAscii() function.
You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator+=().
Appends the character ch to the string.
Returns true if this string is lexically less than string other; otherwise returns false.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare() function.
This function overloads operator<().
This function overloads operator<().
The other byte array is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator<().
The other const char pointer is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
Returns true if this string is lexically less than or equal to string other; otherwise returns false.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().
This function overloads operator<=().
This function overloads operator<=().
The other byte array is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator<=().
The other const char pointer is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
Assigns other to this string and returns a reference to this string.
This function overloads operator=().
Assigns the Latin-1 string str to this string.
This function overloads operator=().
Assigns ba to this string. The byte array is converted to Unicode using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator=().
Assigns str to this string. The const char pointer is converted to Unicode using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator=().
Assigns character ch to this string. The character is converted to Unicode using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator=().
Sets the string to contain the single character ch.
Returns true if string other is equal to this string; otherwise returns false.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().
This function overloads operator==().
This function overloads operator==().
The other byte array is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator==().
The other const char pointer is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
Returns true if this string is lexically greater than string other; otherwise returns false.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().
This function overloads operator>().
This function overloads operator>().
The other byte array is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator>().
The other const char pointer is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
Returns true if this string is lexically greater than or equal to string other; otherwise returns false.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with localeAwareCompare().
This function overloads operator>=().
This function overloads operator>=().
The other byte array is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
This function overloads operator>=().
The other const char pointer is converted to a QString using the fromAscii() function.
You can disable this operator by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.
Returns the character at the specified position in the string as a modifiable reference.
Example:
QString str; if (str[0] == QChar('?')) str[0] = QChar('_');
The return value is of type QCharRef, a helper class for QString. When you get an object of type QCharRef, you can use it as if it were a QChar &. If you assign to it, the assignment will apply to the character in the QString from which you got the reference.
See also at().
This function overloads operator[]().
This function overloads operator[]().
Returns the character at the specified position in the string as a modifiable reference. Equivalent to at(position).
This function overloads operator[]().
Returns true if s1 is not equal to s2; otherwise returns false.
For s1 != 0, this is equivalent to compare( s1, s2 ) != 0. Note that no string is equal to s1 being 0.
See also QString::compare().
Returns a string which is the result of concatenating s1 and s2.
Returns a string which is the result of concatenating s1 and s2 (s2 is converted to Unicode using the QString::fromAscii() function).
See also QString::fromAscii().
Returns a string which is the result of concatenating s1 and s2 (s1 is converted to Unicode using the QString::fromAscii() function).
See also QString::fromAscii().
Returns a string which is the result of concatenating the character ch and the string s.
Returns a string which is the result of concatenating the string s and the character ch.
Returns true if s1 is lexically less than s2; otherwise returns false. For s1 != 0, this is equivalent to compare(s1, s2) < 0.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare() function.
See also QString::compare().
Writes the given string to the specified stream.
See also Format of the QDataStream Operators.
Returns true if s1 is lexically less than or equal to s2; otherwise returns false. For s1 != 0, this is equivalent to compare(s1, s2) <= 0.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings with QString::localeAwareCompare().
See also QString::compare().
This function overloads operator==().
Returns true if s1 is equal to s2; otherwise returns false. Note that no string is equal to s1 being 0.
Equivalent to s1 != 0 && compare(s1, s2) == 0.
See also QString::compare().
Returns true if s1 is lexically greater than s2; otherwise returns false. Equivalent to compare(s1, s2) > 0.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare() function.
See also QString::compare().
Returns true if s1 is lexically greater than or equal to s2; otherwise returns false. For s1 != 0, this is equivalent to compare(s1, s2) >= 0.
The comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-interface strings using the QString::localeAwareCompare() function.
Reads a string from the specified stream into the given string.
See also Format of the QDataStream Operators.
Disables automatic conversions from 8-bit strings (char *) to unicode QStrings
See also QT_NO_CAST_TO_ASCII and QT_NO_CAST_FROM_BYTEARRAY.
disables automatic conversion from QString to ASCII 8-bit strings (char *)
See also QT_NO_CAST_FROM_ASCII and QT_NO_CAST_FROM_BYTEARRAY.
Copyright © 2009 Nokia Corporation and/or its subsidiary(-ies) | Trademarks | Qt 4.6.0 |
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