| Classes - Annotated - Tree - Functions - Home - Structure

# QString Class Reference

The QString class provides an abstraction of Unicode text and the classic C null-terminated char array (char*). More...

`#include <qstring.h>`

Inherited by QConstString.

List of all member functions.

## Public Members

- QString ()
- QString ( QChar )
- QString ( const QString & )
- QString ( const QByteArray & )
- QString ( const QChar * unicode, uint length )
- QString ( const char * str )
- ~QString ()
- QString& operator= ( const QString & )
- QString& operator= ( const char * )
- QString& operator= ( const QCString & )
- QString& operator= ( QChar c )
- QString& operator= ( char c )
- bool isNull () const
- bool isEmpty () const
- uint length () const
- void truncate ( uint pos )
- void fill ( QChar c, int len = -1 )
- QString copy () const (obsolete)
- QString arg ( long a, int fieldwidth=0, int base=10 ) const
- QString arg ( ulong a, int fieldwidth=0, int base=10 ) const
- QString arg ( int a, int fieldwidth=0, int base=10 ) const
- QString arg ( uint a, int fieldwidth=0, int base=10 ) const
- QString arg ( short a, int fieldwidth=0, int base=10 ) const
- QString arg ( ushort a, int fieldwidth=0, int base=10 ) const
- QString arg ( char a, int fieldwidth=0 ) const
- QString arg ( QChar a, int fieldwidth=0 ) const
- QString arg ( const QString & a, int fieldwidth=0 ) const
- QString arg ( double a, int fieldwidth=0, char fmt='g', int prec=-1 ) const
- QString& sprintf ( const char * format, ... )
- int find ( QChar c, int index=0, bool cs=TRUE ) const
- int find ( char c, int index=0, bool cs=TRUE ) const
- int find ( const QString & str, int index=0, bool cs=TRUE ) const
- int find ( const QRegExp &, int index=0 ) const
- int find ( const char * str, int index=0 ) const
- int findRev ( QChar c, int index=-1, bool cs=TRUE ) const
- int findRev ( char c, int index=-1, bool cs=TRUE ) const
- int findRev ( const QString & str, int index=-1, bool cs=TRUE ) const
- int findRev ( const QRegExp &, int index=-1 ) const
- int findRev ( const char * str, int index=-1 ) const
- int contains ( QChar c, bool cs=TRUE ) const
- int contains ( char c, bool cs=TRUE ) const
- int contains ( const char * str, bool cs=TRUE ) const
- int contains ( const QString & str, bool cs=TRUE ) const
- int contains ( const QRegExp & ) const
- QString left ( uint len ) const
- QString right ( uint len ) const
- QString mid ( uint index, uint len=0xffffffff ) const
- QString leftJustify ( uint width, QChar fill=' ', bool trunc=FALSE ) const
- QString rightJustify ( uint width, QChar fill=' ', bool trunc=FALSE ) const
- QString lower () const
- QString upper () const
- QString stripWhiteSpace () const
- QString simplifyWhiteSpace () const
- QString& insert ( uint index, const QString & )
- QString& insert ( uint index, const QChar *, uint len )
- QString& insert ( uint index, QChar )
- QString& insert ( uint index, char c )
- QString& append ( char )
- QString& append ( QChar )
- QString& append ( const QString & )
- QString& prepend ( char )
- QString& prepend ( QChar )
- QString& prepend ( const QString & )
- QString& remove ( uint index, uint len )
- QString& replace ( uint index, uint len, const QString & )
- QString& replace ( uint index, uint len, const QChar *, uint clen )
- QString& replace ( const QRegExp &, const QString & )
- short toShort ( bool * ok=0, int base=10 ) const
- ushort toUShort ( bool * ok=0, int base=10 ) const
- int toInt ( bool * ok=0, int base=10 ) const
- uint toUInt ( bool * ok=0, int base=10 ) const
- long toLong ( bool * ok=0, int base=10 ) const
- ulong toULong ( bool * ok=0, int base=10 ) const
- float toFloat ( bool * ok=0 ) const
- double toDouble ( bool * ok=0 ) const
- QString& setNum ( short, int base=10 )
- QString& setNum ( ushort, int base=10 )
- QString& setNum ( int, int base=10 )
- QString& setNum ( uint, int base=10 )
- QString& setNum ( long, int base=10 )
- QString& setNum ( ulong, int base=10 )
- QString& setNum ( float, char f='g', int prec=6 )
- QString& setNum ( double, char f='g', int prec=6 )
- void setExpand ( uint index, QChar c ) (obsolete)
- QString& operator+= ( const QString & str )
- QString& operator+= ( QChar c )
- QString& operator+= ( char c )
- QChar at ( uint i ) const
- QChar operator[] ( int i ) const
- QCharRef at ( uint i )
- QCharRef operator[] ( int i )
- QChar constref ( uint i ) const
- QChar& ref ( uint i )
- const QChar* unicode () const
- const char* ascii () const (obsolete)
- const char* latin1 () const
- QCString utf8 () const
- QCString local8Bit () const
- bool operator! () const
- operator const char* ()const
- QString& setUnicode ( const QChar * unicode, uint len )
- QString& setUnicodeCodes ( const ushort * unicode_as_ushorts, uint len )
- QString& setLatin1 ( const char *, int len=-1 )
- int compare ( const QString & s ) const
- void compose ()
- QChar::Direction basicDirection ()
- QString visual ( int index = 0, int len = -1 )
- bool startsWith ( const QString & ) const

## Static Public Members

- QString number ( long, int base=10 )
- QString number ( ulong, int base=10 )
- QString number ( int, int base=10 )
- QString number ( uint, int base=10 )
- QString number ( double, char f='g', int prec=6 )
- QString fromLatin1 ( const char *, int len=-1 )
- QString fromUtf8 ( const char *, int len=-1 )
- QString fromLocal8Bit ( const char *, int len=-1 )
- int compare ( const QString & s1, const QString & s2 )

## Related Functions

(Note that these are not member functions.)

- bool operator== (const char * s1, const QString & s2)
- QDataStream & operator<< (QDataStream & s, const QString & str)
- bool operator<= (const char * s1, const QString & s2)
- bool operator< (const QString & s1, const char * s2)
- bool operator> (const QString & s1, const char * s2)
- QString operator+ (char c, const QString & s)
- bool operator>= (const QString & s1, const char * s2)
- bool operator< (const char * s1, const QString & s2)
- QString operator+ (const QString & s1, const char * s2)
- bool operator== (const QString & s1, const char * s2)
- bool operator<= (const QString & s1, const char * s2)
- bool operator== (const QString & s1, const QString & s2)
- bool operator!= (const char * s1, const QString & s2)
- QDataStream & operator>> (QDataStream & s, QString & str)
- bool operator!= (const QString & s1, const QString & s2)
- bool operator>= (const char * s1, const QString & s2)
- bool operator!= (const QString & s1, const char * s2)
- QString operator+ (const QString & s1, const QString & s2)
- QString operator+ (const QString & s, char c)
- bool operator> (const char * s1, const QString & s2)
- QString operator+ (const char * s1, const QString & s2)

## Detailed Description

The QString class provides an abstraction of Unicode text and the classic C null-terminated char array (char*).

QString uses implicit sharing, and so it is very efficient and easy to use.

In all QString methods that take const char* parameters, the const char* is interpreted as a classic C-style 0-terminated ASCII string. It is legal for the const char* parameter to be 0. The results are undefined if the const char* string is not 0-terminated. Functions that copy classic C strings into a QString will not copy the terminating 0-character. The QChar array of the QString (as returned by unicode()) is not terminated by a null.

A QString that has not been assigned to anything is null, i.e. both the length and data pointer is 0. A QString that references the empty string ("", a single '\0' char) is empty. Both null and empty QStrings are legal parameters to the methods. Assigning const char * 0 to QString gives a null QString.

Note that if you find that you are mixing usage of QCString, QString, and QByteArray, this causes lots of unnecessary copying and might indicate that the true nature of the data you are dealing with is uncertain. If the data is NUL-terminated 8-bit data, use QCString; if it is unterminated (ie. contains NULs) 8-bit data, use QByteArray; if it is text, use QString.

See also QChar and Shared classes

Examples: showimg/main.cpp grapher/grapher.cpp xform/xform.cpp layout/layout.cpp helpviewer/main.cpp life/main.cpp i18n/main.cpp drawdemo/drawdemo.cpp popup/popup.cpp menu/menu.cpp progress/progress.cpp qmag/qmag.cpp forever/forever.cpp rot13/rot13.cpp desktop/desktop.cpp scrollview/scrollview.cpp movies/main.cpp picture/picture.cpp hello/main.cpp

## Member Function Documentation

### QString::QString ()

Constructs a null string.

See also isNull().

### QString::QString ( QChar ch )

Constructs a string containing the one character ch.

### QString::QString ( const QByteArray & ba )

Constructs a string that is a deep copy of ba interpreted as a classic C string.

### QString::QString ( const QChar * unicode, uint length )

Constructs a string that is a deep copy of the first length QChar in the array unicode.

If unicode and length are 0, a null string is created.

If only unicode is 0, the string is empty, but has length characters of space preallocated - QString expands automatically anyway, but this may speed some cases up a little.

See also isNull().

### QString::QString ( const QString & s )

Constructs an implicitly-shared copy of s.

### QString::QString ( const char * str )

Constructs a string that is a deep copy of str, interpreted as a classic C string.

If str is 0 a null string is created.

This is a cast constructor, but it is perfectly safe: converting a Latin1 const char* to QString preserves all the information. You can disable this constructor by defining QT_NO_CAST_ASCII when you compile your applications. You can also make QString objects by using setLatin1()/fromLatin1(), or fromLocal8Bit(), fromUtf8(), or whatever encoding is appropriate for the 8-bit data you have.

See also isNull().

### QString::~QString ()

Destroys the string and frees the "real" string, if this was the last copy of that string.

### QString::operator const char * () const

Returns latin1(). Be sure to see the warnings documented there. Note that for new code which you wish to be strictly Unicode-clean, you can define the macro QT_NO_ASCII_CAST when compiling your code to hide this function so that automatic casts are not done. This has the added advantage that you catch the programming error described under operator!().

### QString& QString::append ( QChar ch )

Appends ch to the string and returns a reference to the result. Equivalent to operator+=().

### QString& QString::append ( char ch )

Appends ch to the string and returns a reference to the result. Equivalent to operator+=().

### QString& QString::append ( const QString & str )

Appends str to the string and returns a reference to the result. Equivalent to operator+=().

### QString QString::arg ( const QString & a, int fieldwidth=0 ) const

Returns a string equal to this one, but with the lowest-numbered occurrence of `%i` (for a positive integer i) replaced by a.

        label.setText( tr("Rename %1 to %2?").arg(oldName).arg(newName) );

fieldwidth is the minimum amount of space a is padded to. A positive value produces right-aligned text, while a negative value produces left aligned text.

Warning: Using arg() for constructing "real" sentences programmatically is likely to lead to translation problems. Inserting objects like numbers or file names is fairly safe.

Warning: Relying on spaces to create alignment is prone to lead to translation problems.

If there is no `%i` pattern, a warning message (qWarning()) is printed and the text as appended at the end of the string. This is error recovery and should not occur in correct code.

See also QObject::tr().

### QString QString::arg ( QChar a, int fieldwidth=0 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

### QString QString::arg ( char a, int fieldwidth=0 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

a is assumed to be in the Latin1 character set.

### QString QString::arg ( double a, int fieldwidth=0, char fmt='g', int prec=-1 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

is formatted according to the fmt format specified, which is 'g' by default and can be any of 'f', 'F', 'e', 'E', 'g' or 'G', all of which have the same meaning as for sprintf(). prec determines the precision, just as for number() and sprintf().

### QString QString::arg ( int a, int fieldwidth=0, int base=10 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

a is expressed in to base notation, which is decimal by default and must be in the range 2-36 inclusive.

### QString QString::arg ( long a, int fieldwidth=0, int base=10 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

a is expressed in to base notation, which is decimal by default and must be in the range 2-36 inclusive.

### QString QString::arg ( short a, int fieldwidth=0, int base=10 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

a is expressed in to base notation, which is decimal by default and must be in the range 2-36 inclusive.

### QString QString::arg ( uint a, int fieldwidth=0, int base=10 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

a is expressed in to base notation, which is decimal by default and must be in the range 2-36 inclusive.

### QString QString::arg ( ulong a, int fieldwidth=0, int base=10 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

a is expressed in to base notation, which is decimal by default and must be in the range 2-36 inclusive.

### QString QString::arg ( ushort a, int fieldwidth=0, int base=10 ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

a is expressed in to base notation, which is decimal by default and must be in the range 2-36 inclusive.

### const char* QString::ascii () const

This function is obsolete. It is provided to keep old source working, and will probably be removed in a future version of Qt. We strongly advise against using it in new code.

This functions simply calls latin1() and returns the result.

### QChar QString::at ( uint ) const

Returns the character at i, or 0 if i is beyond the length of the string.

Note: If this QString is not const or const&, the non-const at() will be used instead, which will expand the string if i is beyond the length of the string.

### QCharRef QString::at ( uint i )

Returns a reference to the character at i, expanding the string with QChar::null if necessary. The resulting reference can then be assigned to, or otherwise used immediately, but becomes invalid once further modifications are made to the string.

### QChar::Direction QString::basicDirection()

This function returns the basic directionality of the string (QChar::DirR for right to left and QChar::DirL for left to right). Useful to find the right alignment.

### int QString::compare ( const QString & s ) const

Compares this string to s, returning an integer less than, equal to, or greater than zero if it is, respectively, lexically less than, equal to, or greater than s.

### int QString::compare ( const QString & s1, const QString & s2 ) `[static]`

Compare s1 to s2 returning an integer less than, equal to, or greater than zero if s1 is, respectively, lexically less than, equal to, or greater than s2.

### void QString::compose ()

Note that this function is not supported in Qt 2.0, and is merely for experimental and illustrative purposes. It is mainly of interest to those experimenting with Arabic and other composition-rich texts.

Applies possible ligatures to a QString, useful when composition-rich text requires rendering with glyph-poor fonts, but also makes compositions such as QChar(0x0041) ('A') and QChar(0x0308) (Unicode accent diaresis) giving QChar(0x00c4) (German A Umlaut).

### QChar QString::constref ( uint i ) const

Equivalent to at(i), this returns the QChar at i by value.

See also ref().

### int QString::contains ( QChar c, bool cs=TRUE ) const

Returns the number of times the character c occurs in the string.

The match is case sensitive if cs is TRUE, or case insensitive if cs is FALSE.

### int QString::contains ( const QRegExp & rx ) const

Counts the number of overlapping occurrences of rx in the string.

Example:

        QString s = "banana and panama";
        QRegExp r = QRegExp("a[nm]a", TRUE, FALSE);
        s.contains( r );                            // 4 matches

See also find() and findRev().

### int QString::contains ( const QString & str, bool cs=TRUE ) const

Returns the number of times str occurs in the string.

The match is case sensitive if cs is TRUE, or case insensitive if cs is FALSE.

This function counts overlapping substrings, for example, "banana" contains two occurrences of "ana".

See also findRev().

### int QString::contains ( char c, bool cs=TRUE ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

### int QString::contains ( const char * str, bool cs=TRUE ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

### QString QString::copy () const

This function is obsolete. It is provided to keep old source working, and will probably be removed in a future version of Qt. We strongly advise against using it in new code.

Returns a deep copy of this string.

Doing this is redundant in Qt 2.x, since QString is implicitly shared, and so will automatically be deeply copied as necessary.

### void QString::fill ( QChar c, int len = -1 )

Fills the string with len characters of value c.

If len is negative, the current string length is used.

### int QString::find ( QChar c, int index=0, bool cs=TRUE ) const

Finds the first occurrence of the character c, starting at position index. If index is -1, the search starts at the last character; if -2, at the next to last character; etc.

The search is case sensitive if cs is TRUE, or case insensitive if cs is FALSE.

Returns the position of c, or -1 if c could not be found.

### int QString::find ( const QRegExp & rx, int index=0 ) const

Finds the first occurrence of the regular expression rx, starting at position index. If index is -1, the search starts at the last character; if -2, at the next to last character; etc.

Returns the position of the next match, or -1 if rx was not found.

See also findRev(), replace() and contains().

### int QString::find ( const QString & str, int index=0, bool cs=TRUE ) const

Finds the first occurrence of the string str, starting at position index. If index is -1, the search starts at the last character; if -2, at the next to last character; etc.

The search is case sensitive if cs is TRUE, or case insensitive if cs is FALSE.

Returns the position of str, or -1 if str could not be found.

### int QString::find ( const char * str, int index=0 ) const

Equivalent to find(QString(str), index).

### int QString::find ( char c, int index=0, bool cs=TRUE ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

### int QString::findRev ( QChar c, int index=-1, bool cs=TRUE ) const

Finds the first occurrence of the character c, starting at position index and searching backwards. If index is -1, the search starts at the last character; if -2, at the next to last character; etc.

The search is case sensitive if cs is TRUE, or case insensitive if cs is FALSE.

Returns the position of c, or -1 if c could not be found.

### int QString::findRev ( const QRegExp & rx, int index=-1 ) const

Finds the first occurrence of the regular expression rx, starting at position index and searching backwards. If index is -1, the search starts at the last character; if -2, at the next to last character; etc.

Returns the position of the next match (backwards), or -1 if rx was not found.

See also find().

### int QString::findRev ( const QString & str, int index=-1, bool cs=TRUE ) const

Finds the first occurrence of the string str, starting at position index and searching backwards. If index is -1, the search starts at the last character; -2, at the next to last character; etc.

The search is case sensitive if cs is TRUE, or case insensitive if cs is FALSE.

Returns the position of str, or -1 if str could not be found.

### int QString::findRev ( const char * str, int index=-1 ) const

Equivalent to findRev(QString(str), index).

### int QString::findRev ( char c, int index=-1, bool cs=TRUE ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

### QString QString::fromLatin1 ( const char * chars, int len=-1 ) `[static]`

Creates a QString from Latin1 text. This is the same as the QString(const char*) constructor, but you can make that constructor invisible if you compile with the define QT_NO_CAST_ASCII, in which case you can explicitly create a QString from Latin-1 text using this function.

### QString QString::fromLocal8Bit ( const char * local8Bit, int len=-1 ) `[static]`

Returns the unicode string decoded from the first len bytes of local8Bit. If len is -1 (the default), the length of local8Bit is used. If trailing partial characters are in local8Bit, they are ignored.

local8Bit is assumed to be encoded in a locale-specific format.

See QTextCodec for more diverse coding/decoding of Unicode strings.

### QString QString::fromUtf8 ( const char * utf8, int len=-1 ) `[static]`

Returns the unicode string decoded from the first len bytes of utf8. If len is -1 (the default), the length of utf8 is used. If trailing partial characters are in utf8, they are ignored.

See QTextCodec for more diverse coding/decoding of Unicode strings.

### QString & QString::insert ( uint index, QChar c )

Insert c into the string at (before) position index and returns a reference to the string.

If index is beyond the end of the string, the string is extended with spaces (ASCII 32) to length index and c is then appended.

Example:

        QString s = "Ys";
        s.insert( 1, 'e' );         // s == "Yes"
        s.insert( 3, '!');          // s == "Yes!"

See also remove() and replace().

Examples: xform/xform.cpp

### QString & QString::insert ( uint index, const QChar * s, uint len )

Insert len units of QChar data from s into the string before position index.

### QString & QString::insert ( uint index, const QString & s )

Insert s into the string before position index.

If index is beyond the end of the string, the string is extended with spaces (ASCII 32) to length index and s is then appended.

        QString s = "I like fish";
        s.insert( 2, "don't ");     // s == "I don't like fish"
        s = "x";
        s.insert( 3, "yz" );        // s == "x  yz"

### QString& QString::insert ( uint index, char c )

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

### bool QString::isEmpty () const

Returns TRUE if the string is empty, i.e. if length() == 0. An empty string is not always a null string.

See example in isNull().

See also isNull() and length().

Examples: qmag/qmag.cpp hello/main.cpp

### bool QString::isNull () const

Returns TRUE if the string is null. A null string is also an empty string.

Example:

        QString a;          // a.unicode() == 0,  a.length() == 0
        QString b = "";     // b.unicode() == "", b.length() == 0
        a.isNull();         // TRUE, because a.unicode() == 0
        a.isEmpty();        // TRUE, because a.length() == 0
        b.isNull();         // FALSE, because b.unicode() != 0
        b.isEmpty();        // TRUE, because b.length() == 0

See also isEmpty() and length().

### const char* QString::latin1 () const

Returns a Latin-1 representation of the string. Note that the returned value is undefined if the string contains non-Latin-1 characters. If you want to convert strings into formats other than Unicode, see the QTextCodec classes.

This function is mainly useful for boot-strapping legacy code to use Unicode.

The result remains valid so long as one unmodified copy of the source string exists.

See also utf8() and local8Bit().

### QString QString::left ( uint len ) const

Returns a substring that contains the len leftmost characters of the string.

The whole string is returned if len exceeds the length of the string.

Example:

        QString s = "Pineapple";
        QString t = s.left( 4 );    // t == "Pine"

See also right(), mid() and isEmpty().

### QString QString::leftJustify ( uint width, QChar fill=' ', bool truncate=FALSE ) const

Returns a string of length width that contains this string and padded by the fill character.

If the length of the string exceeds width and truncate is FALSE, then the returned string is a copy of the string. If the length of the string exceeds width and truncate is TRUE, then the returned string is a left(width).

Example:

        QString s("apple");
        QString t = s.leftJustify(8, '.');          // t == "apple..."

See also rightJustify().

### uint QString::length () const

Returns the length of the string.

Null strings and empty strings have zero length.

See also isNull() and isEmpty().

### QCString QString::local8Bit () const

Returns the string encoded in a locale-specific format. On X11, this is the QTextCodec::codecForLocale(). On Windows, it is a system-defined encoding.

See QTextCodec for more diverse coding/decoding of Unicode strings.

See also QString::fromLocal8Bit(), latin1() and utf8().

### QString QString::lower () const

Returns a new string that is the string converted to lower case.

Example:

        QString s("TeX");
        QString t = s.lower();      // t == "tex"

See also upper().

### QString QString::mid ( uint index, uint len=0xffffffff ) const

Returns a substring that contains the len characters of this string, starting at position index.

Returns a null string if the string is empty or index is out of range. Returns the whole string from index if index+len exceeds the length of the string.

Example:

        QString s = "Five pineapples";
        QString t = s.mid( 5, 4 );                  // t == "pine"

See also left() and right().

Examples: qmag/qmag.cpp

### QString QString::number ( double n, char f='g', int prec=6 ) `[static]`

This static function returns the printed value of n, formatted in the f format with prec precision.

f can be 'f', 'F', 'e', 'E', 'g' or 'G', all of which have the same meaning as for sprintf().

See also setNum().

### QString QString::number ( int n, int base=10 ) `[static]`

A convenience factory function that returns a string representation of the number n.

See also setNum().

### QString QString::number ( long n, int base=10 ) `[static]`

A convenience factory function that returns a string representation of the number n.

See also setNum().

### QString QString::number ( uint n, int base=10 ) `[static]`

A convenience factory function that returns a string representation of the number n.

See also setNum().

### QString QString::number ( ulong n, int base=10 ) `[static]`

A convenience factory function that returns a string representation of the number n.

See also setNum().

### bool QString::operator! () const

Returns TRUE if it is a null string, otherwise FALSE. Thus you can write:

      QString name = getName();
      if ( !name )
        name = "Rodney";

Note that if you say:

      QString name = getName();
      if ( name )
        doSomethingWith(name);

Then this will call `operator const char*()`, which will do what you want, but rather inefficiently - you may wish to define the macro QT_NO_ASCII_CAST when writing code which you wish to strictly remain Unicode-clean.

When you want the above semantics, use `!isNull()` or even `!!`:

      QString name = getName();
      if ( !!name )
        doSomethingWith(name);

### QString & QString::operator+= ( QChar c )

Appends c to the string and returns a reference to the string.

### QString & QString::operator+= ( char c )

Appends c to the string and returns a reference to the string.

### QString& QString::operator+= ( const QString & str )

Appends str to the string and returns a reference to the string.

### QString & QString::operator= ( const QCString & cs )

Assigns a deep copy of cs, interpreted as a classic C string, to this string and returns a reference to this string.

### QString & QString::operator= ( const QString & s )

Assigns a shallow copy of s to this string and returns a reference to this string.

### QString & QString::operator= ( const char * str )

Assigns a deep copy of str, interpreted as a classic C string, to this string and returns a reference to this string.

If str is 0 a null string is created.

See also isNull().

### QString& QString::operator= ( QChar c )

Sets the string to contain just the single character c.

### QString& QString::operator= ( char c )

Sets the string to contain just the single character c.

### QChar QString::operator[] ( int ) const

Returns the character at i, or QChar::null if i is beyond the length of the string.

Note: If this QString is not const or const&, the non-const operator[] will be used instead, which will expand the string if i is beyond the length of the string.

### QCharRef QString::operator[] ( int )

Returns an object that references the character at i. This reference can then be assigned to, or otherwise used immediately, but becomes invalid once further modifications are made to the string. The QCharRef internal class can be used much like a constant QChar, but if you assign to it, you change the original string (which enlarges and detaches itself). You will get compilation errors if you try to use the result as anything but a QChar.

### QString & QString::prepend ( const QString & s )

Prepend s to the string. Equivalent to insert(0,s).

See also insert().

### QString& QString::prepend ( QChar ch )

Prepends ch to the string and returns a reference to the result.

See also insert().

### QString& QString::prepend ( char ch )

Prepends ch to the string and returns a reference to the result.

See also insert().

### QChar& QString::ref ( uint i )

Returns the QChar at i by reference.

See also constref().

### QString & QString::remove ( uint index, uint len )

Removes len characters starting at position index from the string and returns a reference to the string.

If index is too big, nothing happens. If index is valid, but len is too large, the rest of the string is removed.

        QString s = "Montreal";
        s.remove( 1, 4 );
        // s == "Meal"

See also insert() and replace().

### QString & QString::replace ( const QRegExp & rx, const QString & str )

Replaces every occurrence of rx in the string with str. Returns a reference to the string.

Examples:

        QString s = "banana";
        s.replace( QRegExp("a.*a"), "" );           // becomes "b"

        QString s = "banana";
        s.replace( QRegExp("^[bn]a"), " " );        // becomes " nana"

        QString s = "banana";
        s.replace( QRegExp("^[bn]a"), "" );         // NOTE! becomes ""

See also find() and findRev(). qmag/qmag.cpp

### QString & QString::replace ( uint index, uint len, const QChar * s, uint slen )

Replaces len characters starting at position index by slen units ot QChar data from s, and returns a reference to the string.

See also insert() and remove().

### QString & QString::replace ( uint index, uint len, const QString & s )

Replaces len characters starting at position index from the string with s, and returns a reference to the string.

If index is too big, nothing is deleted and s is inserted at the end of the string. If index is valid, but len is too large, str replaces the rest of the string.

        QString s = "Say yes!";
        s.replace( 4, 3, "NO" );                    // s == "Say NO!"

See also insert() and remove().

### QString QString::right ( uint len ) const

Returns a substring that contains the len rightmost characters of the string.

The whole string is returned if len exceeds the length of the string.

Example:

        QString s = "Pineapple";
        QString t = s.right( 5 );   // t == "apple"

See also left(), mid() and isEmpty().

### QString QString::rightJustify ( uint width, QChar fill=' ', bool truncate=FALSE ) const

Returns a string of length width that contains pad characters followed by the string.

If the length of the string exceeds width and truncate is FALSE, then the returned string is a copy of the string. If the length of the string exceeds width and truncate is TRUE, then the returned string is a left(width).

Example:

        QString s("pie");
        QString t = s.rightJustify(8, '.');         // t == ".....pie"

See also leftJustify().

### void QString::setExpand ( uint index, QChar c )

This function is obsolete. It is provided to keep old source working, and will probably be removed in a future version of Qt. We strongly advise against using it in new code.

Sets the character at position index to c and expands the string if necessary, filling with spaces.

This method is redundant in Qt 2.x, because operator[] will expand the string as necessary.

### QString & QString::setLatin1 ( const char * str, int len=-1 )

Sets this string to str, interpreted as a classic Latin 1 C string. If the len argument is negative (default), it is set to strlen(str).

If str is 0 a null string is created. If str is "" an empty string is created.

See also isNull() and isEmpty().

### QString & QString::setNum ( double n, char f='g', int prec=6 )

Sets the string to the printed value of n, formatted in the f format with prec precision, and returns a reference to the string.

f can be 'f', 'F', 'e', 'E', 'g' or 'G', all of which have the same meaning as for sprintf().

### QString & QString::setNum ( int n, int base=10 )

Sets the string to the printed value of n and returns a reference to the string.

### QString & QString::setNum ( long n, int base=10 )

Sets the string to the printed value of n and returns a reference to the string.

The value is converted to base notation (default is decimal). The base must be a value from 2 to 36.

### QString & QString::setNum ( short n, int base=10 )

Sets the string to the printed value of n and returns a reference to the string.

### QString & QString::setNum ( uint n, int base=10 )

Sets the string to the printed unsigned value of n and returns a reference to the string.

### QString & QString::setNum ( ulong n, int base=10 )

Sets the string to the printed unsigned value of n and returns a reference to the string.

The value is converted to base notation (default is decimal). The base must be a value from 2 to 36.

### QString & QString::setNum ( ushort n, int base=10 )

Sets the string to the printed unsigned value of n and returns a reference to the string.

### QString & QString::setNum ( float n, char f='g', int prec=6 )

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

### QString& QString::setUnicode ( const QChar * unicode, uint len )

Resizes the string to len unicode characters and copies unicode into the string. If unicode is null, nothing is copied, but the string is resized to len anyway. If len is zero, the string becomes a null string.

See also setLatin1() and isNull().

### QString& QString::setUnicodeCodes ( const ushort * unicode_as_ushorts, uint len )

Resizes the string to len unicode characters and copies unicode_as_ushorts into the string (on some X11 client platforms this will involve a byte-swapping pass).

If unicode is null, nothing is copied, but the string is resized to len anyway. If len is zero, the string becomes a null string.

See also setLatin1() and isNull().

### QString QString::simplifyWhiteSpace () const

Returns a new string that has white space removed from the start and the end, plus any sequence of internal white space replaced with a single space (ASCII 32).

White space means any character for which QChar::isSpace() returns TRUE. This includes ASCII characters 9 (TAB), 10 (LF), 11 (VT), 12 (FF), 13 (CR), and 32 (Space).

        QString s = "  lots\t of\nwhite    space ";
        QString t = s.simplifyWhiteSpace();         // t == "lots of white space"

See also stripWhiteSpace().

### QString & QString::sprintf ( const char * cformat, ... )

Safely builds a formatted string from a format string and an arbitrary list of arguments. The format string supports all the escape sequences of printf() in the standard C library.

The %s escape sequence expects a utf8() encoded string. The format string cformat is expected to be in latin1. If you need a unicode format string, use QString::arg() instead. For typesafe string building, with full Unicode support, you can use QTextOStream like this:

        QString str;
        QString s = ...;
        int x = ...;
        QTextOStream(&str) << s << " : " << x;

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, and has Unicode support.

See also arg().

Examples: xform/xform.cpp layout/layout.cpp drawdemo/drawdemo.cpp popup/popup.cpp progress/progress.cpp qmag/qmag.cpp forever/forever.cpp scrollview/scrollview.cpp movies/main.cpp picture/picture.cpp

### bool QString::startsWith ( const QString & s ) const

Returns whether the strings starts with s, or not.

### QString QString::stripWhiteSpace () const

Returns a new string that has white space removed from the start and the end.

White space means any character for which QChar::isSpace() returns TRUE. This includes ASCII characters 9 (TAB), 10 (LF), 11 (VT), 12 (FF), 13 (CR), and 32 (Space).

Example:

        QString s = " space ";
        QString t = s.stripWhiteSpace();            // t == "space"

See also simplifyWhiteSpace().

### double QString::toDouble ( bool * ok=0 ) const

Returns the string converted to a `double` value.

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### float QString::toFloat ( bool * ok=0 ) const

Returns the string converted to a `float` value.

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### int QString::toInt ( bool * ok=0, int base=10 ) const

Returns the string converted to a `int` value.

      QString str("FF");
      bool ok;
      int hex = str.toInt( &ok, 16 ); // will return 255, and ok set to TRUE
      int dec = str.toInt( &ok, 10 ); // will return 0, and ok set to FALSE

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### long QString::toLong ( bool * ok=0, int base=10 ) const

Returns the string converted to a `long` value.

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### short QString::toShort ( bool * ok=0, int base=10 ) const

Returns the string converted to a `short` value.

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### uint QString::toUInt ( bool * ok=0, int base=10 ) const

Returns the string converted to an `unsigned int` value.

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### ulong QString::toULong ( bool * ok=0, int base=10 ) const

Returns the string converted to an `unsigned long` value.

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### ushort QString::toUShort ( bool * ok=0, int base=10 ) const

Returns the string converted to an `unsigned short` value.

If ok is non-null, *ok is set to TRUE if there are no conceivable errors, and FALSE if the string is not a number at all, or if it has trailing garbage.

### void QString::truncate ( uint newLen )

Truncates the string at position newLen if newLen is less than the current length . Otherwise, nothing happens.

Example:

        QString s = "truncate this string";
        s.truncate( 5 );                            // s == "trunc"

In Qt 1.x, it was possible to "truncate" a string to a longer length. This is no longer possible.

### const QChar* QString::unicode () const

Returns the Unicode representation of the string. The result remains valid until the string is modified.

### QString QString::upper () const

Returns a new string that is the string converted to upper case.

Example:

        QString s("TeX");
        QString t = s.upper();                      // t == "TEX"

See also lower().

### QCString QString::utf8 () const

Returns the string encoded in UTF8 format.

See QTextCodec for more diverse coding/decoding of Unicode strings.

See also QString::fromUtf8(), local8Bit() and latin1().

### QString QString::visual ( int index = 0, int len = -1 )

This function returns the QString ordered visually. Useful for painting the string or when transforming to a visually ordered encoding.

## Related Functions

### bool operator== (const char * s1, const QString & s2)

Returns TRUE if the two strings are equal, or FALSE if they are different.

Equivalent to `qstrcmp(s1,s2) == 0`

### QDataStream & operator<< (QDataStream & s, const QString & str)

Writes a string to the stream.

See also Format of the QDataStream operators

### bool operator<= (const char * s1, const QString & s2)

Returns TRUE if s1 is alphabetically less than or equal to s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) <= 0`

### bool operator< (const QString & s1, const char * s2)

Returns TRUE if s1 is alphabetically less than s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) < 0`

### bool operator> (const QString & s1, const char * s2)

Returns TRUE if s1 is alphabetically greater than s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) > 0`

### QString operator+ (char c, const QString & s)

Returns the concatenated string of c and s.

### bool operator>= (const QString & s1, const char * s2)

Returns TRUE if s1 is alphabetically greater than or equal to s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) >= 0`

### bool operator< (const char * s1, const QString & s2)

Returns TRUE if s1 is alphabetically less than s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) < 0`

### QString operator+ (const QString & s1, const char * s2)

Returns the concatenated string of s1 and s2.

### bool operator== (const QString & s1, const char * s2)

Returns TRUE if the two strings are equal, or FALSE if they are different.

Equivalent to `qstrcmp(s1,s2) == 0`

### bool operator<= (const QString & s1, const char * s2)

Returns TRUE if s1 is alphabetically less than or equal to s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) <= 0`

### bool operator== (const QString & s1, const QString & s2)

Returns TRUE if the two strings are equal, or FALSE if they are different. A null string is different from an empty, non-null string.

Equivalent to `qstrcmp(s1,s2) == 0`

### bool operator!= (const char * s1, const QString & s2)

Returns TRUE if the two strings are different, or FALSE if they are equal.

Equivalent to `qstrcmp(s1,s2) != 0`

### QDataStream & operator>> (QDataStream & s, QString & str)

Reads a string from the stream.

See also Format of the QDataStream operators

### bool operator!= (const QString & s1, const QString & s2)

Returns TRUE if the two strings are different, or FALSE if they are equal.

Equivalent to `qstrcmp(s1,s2) != 0`

### bool operator>= (const char * s1, const QString & s2)

Returns TRUE if s1 is alphabetically greater than or equal to s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) >= 0`

### bool operator!= (const QString & s1, const char * s2)

Returns TRUE if the two strings are different, or FALSE if they are equal.

Equivalent to `qstrcmp(s1,s2) != 0`

### QString operator+ (const QString & s1, const QString & s2)

Returns the concatenated string of s1 and s2.

### QString operator+ (const QString & s, char c)

Returns the concatenated string of s and c.

### bool operator> (const char * s1, const QString & s2)

Returns TRUE if s1 is alphabetically greater than s2, otherwise FALSE.

Equivalent to `qstrcmp(s1,s2) > 0`

### QString operator+ (const char * s1, const QString & s2)

Returns the concatenated string of s1 and s2.

Search the documentation, FAQ, qt-interest archive and more (uses www.trolltech.com):

This file is part of the Qt toolkit, copyright © 1995-2001 Trolltech, all rights reserved.