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The QString class provides an abstraction of Unicode text and the classic C '\0'-terminated char array. More...
All the functions in this class are reentrant when Qt is built with thread support.
#include <qstring.h>
The QString class provides an abstraction of Unicode text and the classic C '\0'-terminated char array.
QString uses implicit sharing, which makes it very efficient and easy to use.
In all of the 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. If the const char * is not '\0'-terminated, the results are undefined. 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 generally not terminated by a '\0'. If you need to pass a QString to a function that requires a C '\0'-terminated string use latin1().
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. For convenience, QString::null is a null QString. When sorting, empty strings come first, followed by non-empty strings, followed by null strings. We recommend using if ( !str.isNull() ) to check for a non-null string rather than if ( !str ); see operator!() for an explanation.
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 '\0'-terminated 8-bit data, use QCString; if it is unterminated (i.e. contains '\0's) 8-bit data, use QByteArray; if it is text, use QString.
Lists of strings are handled by the QStringList class. You can split a string into a list of strings using QStringList::split(), 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 regex using QStringList::grep().
Note for C programmers
Due to C++'s type system and the fact that QString is implicitly shared, QStrings can be treated like ints or other simple base types. For example:
QString boolToString( bool b )
{
QString result;
if ( b )
result = "True";
else
result = "False";
return result;
}
The variable, result, is an auto variable allocated on the stack. When return is called, 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, see below.)
Throughout Qt's source code you will encounter QString usages like this:
QString func( const QString& input )
{
QString output = input;
// process output
return output;
}
The 'copying' of input to output is almost as fast as copying a pointer because behind the scenes copying is achieved by incrementing a reference count. QString (like all Qt's implicitly shared classes) operates on a copy-on-write basis, only copying if an instance is actually changed.
If you wish to create a deep copy of a QString without losing any Unicode information then you should use QDeepCopy.
See also QChar, QCString, QByteArray, QConstString, Implicitly and Explicitly Shared Classes, Text Related Classes, and Non-GUI Classes.
Any of the last four values can be OR-ed together to form a flag.
See also section().
Constructs a null string, i.e. both the length and data pointer are 0.
See also isNull().
If unicode and length are 0, then 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 up some cases a little. We recommend using the plain constructor and setLength() for this purpose since it will result in more readable code.
See also isNull() and setLength().
If str is 0, then a null string is created.
This is a cast constructor, but it is perfectly safe: converting a Latin-1 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(), fromLocal8Bit(), and fromUtf8(). Or whatever encoding is appropriate for the 8-bit data you have.
See also isNull() and fromAscii().
This is the same as fromAscii(str).
Destroys the string and frees the string's data if this is the last reference to the string.
Appends str to the string and returns a reference to the result.
string = "Test";
string.append( "ing" ); // string == "Testing"
Equivalent to operator+=().
Example: dirview/dirview.cpp.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Appends character ch to the string and returns a reference to the result.
Equivalent to operator+=().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Appends character ch to the string and returns a reference to the result.
Equivalent to operator+=().
Appends str to the string and returns a reference to the result.
Equivalent to operator+=().
Appends str to the string and returns a reference to the result.
Equivalent to operator+=().
Appends str to the string and returns a reference to the result.
Equivalent to operator+=().
The fieldWidth value specifies the minimum amount of space that a is padded to. A positive value will produce right-aligned text, whereas a negative value will produce left-aligned text.
The following example shows how we could create a 'status' string when processing a list of files:
QString status = QString( "Processing file %1 of %2: %3" )
.arg( i ) // current file's number
.arg( total ) // number of files to process
.arg( fileName ); // current file's name
It is generally fine to use filenames and numbers as we have done in the example above. But note that using arg() to construct natural language sentences does not usually translate well into other languages because sentence structure and word order often differ between languages.
If there is no place marker (%1, %2, etc.), a warning message (qWarning()) is output and the result is undefined.
Warning: If any placeholder occurs more than once, the result is undefined.
The fieldWidth value specifies the minimum amount of space that a is padded to. A positive value will produce a right-aligned number, whereas a negative value will produce a left-aligned number.
a is expressed in base 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::English, QLocale::UnitedStates);
str = QString( "%1 %L2 %L3" )
.arg( 12345 )
.arg( 12345 )
.arg( 12345, 0, 16 );
// str == "12345 12,345 3039"
a is expressed in base base, which is 10 by default and must be between 2 and 36. If base is 10, the '%L' syntax can be used to produce localized strings.
a is expressed in base base, which is 10 by default and must be between 2 and 36. If base is 10, the '%L' syntax can be used to produce localized strings.
a is expressed in base base, which is 10 by default and must be between 2 and 36. If base is 10, the '%L' syntax can be used to produce localized strings.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
a is expressed in base base, which is 10 by default and must be between 2 and 36. If base is 10, the '%L' syntax can be used to produce localized strings.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
a is expressed in base base, which is 10 by default and must be between 2 and 36. If base is 10, the '%L' syntax can be used to produce localized strings.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
a is expressed in base base, which is 10 by default and must be between 2 and 36. If base is 10, the '%L' syntax can be used to produce localized strings.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
a is expressed in base base, which is 10 by default and must be between 2 and 36. If base is 10, the '%L' syntax can be used to produce localized strings.
Argument a is formatted according to the fmt format specified, which is 'g' by default and can be any 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 |
With 'e', 'E', and 'f', prec is the number of digits after the decimal point. With 'g' and 'G', prec is the maximum number of significant digits (trailing zeroes are omitted).
double d = 12.34;
QString ds = QString( "'E' format, precision 3, gives %1" )
.arg( d, 0, 'E', 3 );
// ds == "'E' format, precision 3, gives 1.234E+01"
The '%L' syntax can be used to produce localized strings.
a is assumed to be in the Latin-1 character set.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
This is the same as str.arg(a1).arg(a2), except that the strings are replaced in one pass. This can make a difference if a1 contains e.g. %1:
QString str( "%1 %2" );
str.arg( "Hello", "world" ); // returns "Hello world"
str.arg( "Hello" ).arg( "world" ); // returns "Hello world"
str.arg( "(%1)", "Hello" ); // returns "(%1) Hello"
str.arg( "(%1)" ).arg( "Hello" ); // returns "(Hello) %2"
This is the same as calling str.arg(a1).arg(a2).arg(a3), except that the strings are replaced in one pass.
This is the same as calling str.arg(a1).arg(a2).arg(a3).arg(a4), except that the strings are replaced in one pass.
If a codec has been set using QTextCodec::codecForCStrings(), it is used to convert Unicode to 8-bit char. Otherwise, this function does the same as latin1().
See also fromAscii(), latin1(), utf8(), and local8Bit().
Example: network/networkprotocol/nntp.cpp.
Returns the character at index i, or 0 if i is beyond the length of the string.
const QString string( "abcdefgh" );
QChar ch = string.at( 4 );
// ch == 'e'
If the QString is not const (i.e. const QString) or const& (i.e. const QString &), then the non-const overload of at() will be used instead.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
The function returns a reference to the character at index i. The resulting reference can then be assigned to, or used immediately, but it will become invalid once further modifications are made to the original string.
If i is beyond the length of the string then the string is expanded with QChar::null.
Returns the number of characters this string can hold in the allocated memory.
See also reserve() and squeeze().
Lexically 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 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().
int a = QString::compare( "def", "abc" ); // a > 0
int b = QString::compare( "abc", "def" ); // b < 0
int c = QString::compare( "abc", "abc" ); // c == 0
Lexically compares this string with s and returns an integer less than, equal to, or greater than zero if it is less than, equal to, or greater than s.
Applies possible ligatures to a QString. Useful when composition-rich text requires rendering with glyph-poor fonts, but it also makes compositions such as QChar(0x0041) ('A') and QChar(0x0308) (Unicode accent diaresis), giving QChar(0x00c4) (German A Umlaut).
Returns the QChar at index i by value.
Equivalent to at(i).
See also ref().
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
QString string( "Trolltech and Qt" );
int n = string.contains( 't', FALSE );
// n == 3
Examples: fileiconview/qfileiconview.cpp and mdi/application.cpp.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns the number of times the string str occurs in the string.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Returns the number of times str occurs in the string.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
This function counts overlapping strings, so in the example below, there are two instances of "ana" in "bananas".
QString str( "bananas" );
int i = str.contains( "ana" ); // i == 2
See also findRev().
Returns the number of times the regexp, 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";
QRegExp rxp = QRegExp( "a[nm]a", TRUE, FALSE );
int i = str.contains( rxp ); // i == 4
See also find() and findRev().
This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.
In Qt 2.0 and later, all calls to this function are needless. Just remove them.
This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.
Returns a pointer to a '\0'-terminated classic C string.
In Qt 1.x, this returned a char* allowing direct manipulation of the string as a sequence of bytes. In Qt 2.x where QString is a Unicode string, char* conversion constructs a temporary string, and hence direct character operations are meaningless.
If cs is TRUE (the 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().
Example: chart/main.cpp.
If len is negative (the default), the current string length is used.
QString str;
str.fill( 'g', 5 ); // string == "ggggg"
Returns the position of the first match of rx or -1 if no match was found.
QString string( "bananas" );
int i = string.find( QRegExp("an"), 0 ); // i == 1
See also findRev(), replace(), and contains().
Example: network/mail/smtp.cpp.
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 and so on. (See findRev() for searching backwards.)
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Returns the position of c or -1 if c could not be found.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Find character c starting from position index.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Finds the first occurrence of the string str, starting at position index. If index is -1, the search starts at the last character, if it is -2, at the next to last character and so on. (See findRev() for searching backwards.)
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Returns the position of str or -1 if str could not be found.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Equivalent to find(QString(str), index).
Equivalent to findRev(QString(str), index).
Finds the first occurrence of the character c, starting at position index and searching backwards. If the index is -1, the search starts at the last character, if it is -2, at the next to last character and so on.
Returns the position of c or -1 if c could not be found.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
QString string( "bananas" );
int i = string.findRev( 'a' ); // i == 5
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Find character c starting from position index and working backwards.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Finds the first occurrence of the string str, starting at position index and searching backwards. If the index is -1, the search starts at the last character, if it is -2, at the next to last character and so on.
Returns the position of str or -1 if str could not be found.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
QString string("bananas");
int i = string.findRev( "ana" ); // i == 3
Finds the first match of the regexp rx, starting at position index and searching backwards. If the index is -1, the search starts at the last character, if it is -2, at the next to last character and so on. (See findRev() for searching backwards.)
Returns the position of the match or -1 if no match was found.
QString string( "bananas" );
int i = string.findRev( QRegExp("an") ); // i == 3
See also find().
If a codec has been set using QTextCodec::codecForCStrings(), it is used to convert the string from 8-bit characters to Unicode. Otherwise, this function does the same as fromLatin1().
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 8-bit ASCII text using this function.
QString str = QString::fromAscii( "123456789", 5 );
// str == "12345"
See also fromAscii().
Examples: listbox/listbox.cpp and network/mail/smtp.cpp.
QString str = QString::fromLocal8Bit( "123456789", 5 );
// str == "12345"
local8Bit is assumed to be encoded in a locale-specific format.
See QTextCodec for more diverse coding/decoding of Unicode strings.
If str is 0, then a null string is created.
See also isNull().
QString str = QString::fromUtf8( "123456789", 5 );
// str == "12345"
See QTextCodec for more diverse coding/decoding of Unicode strings.
Example: fonts/simple-qfont-demo/viewer.cpp.
If index is beyond the end of the string, the string is extended with spaces to length index and s is then appended and returns a reference to the string.
QString string( "I like fish" );
str = string.insert( 2, "don't " );
// str == "I don't like fish"
See also remove() and replace().
Examples: themes/themes.cpp and xform/xform.cpp.
Inserts s into the string at position index and returns a reference to the string.
Inserts s into the string at position index and returns a reference to the string.
Inserts the first len characters in s into the string at position index and returns a reference to the string.
Insert c into the string at 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.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Insert character c at position index.
Returns TRUE if the string is empty, i.e. if length() == 0; otherwise returns FALSE. Null strings are also empty.
QString a( "" );
a.isEmpty(); // TRUE
a.isNull(); // FALSE
QString b;
b.isEmpty(); // TRUE
b.isNull(); // TRUE
See also isNull() and length().
Examples: addressbook/mainwindow.cpp, chart/chartform.cpp, chart/chartform_canvas.cpp, network/networkprotocol/nntp.cpp, qmag/qmag.cpp, and qwerty/qwerty.cpp.
Returns TRUE if the string is null; otherwise returns FALSE. A null string is always empty.
QString a; // a.unicode() == 0, a.length() == 0
a.isNull(); // TRUE, because a.unicode() == 0
a.isEmpty(); // TRUE, because a.length() == 0
See also isEmpty() and length().
Examples: i18n/main.cpp, network/ftpclient/ftpmainwindow.ui.h, and qdir/qdir.cpp.
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 fromLatin1(), ascii(), utf8(), and local8Bit().
Examples: fileiconview/qfileiconview.cpp and network/networkprotocol/nntp.cpp.
The whole string is returned if len exceeds the length of the string.
QString s = "Pineapple";
QString t = s.left( 4 ); // t == "Pine"
See also right(), mid(), and isEmpty().
Example: themes/themes.cpp.
If truncate is FALSE and the length of the string is more than width, then the returned string is a copy of the string.
If truncate is TRUE and the length of the string is more than width, then any characters in a copy of the string after length width are removed, and the copy is returned.
QString s( "apple" );
QString t = s.leftJustify( 8, '.' ); // t == "apple..."
See also rightJustify().
Returns the length of the string.
Null strings and empty strings have zero length.
See also isNull() and isEmpty().
Examples: dirview/dirview.cpp, fileiconview/qfileiconview.cpp, network/networkprotocol/nntp.cpp, rot13/rot13.cpp, and themes/themes.cpp.
See QTextCodec for more diverse coding/decoding of Unicode strings.
See also fromLocal8Bit(), ascii(), latin1(), and utf8().
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.
See also QString::compare() and QTextCodec::locale().
Compares this string with s.
QString string( "TROlltECH" );
str = string.lower(); // str == "trolltech"
See also upper().
Example: scribble/scribble.cpp.
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.
QString s( "Five pineapples" );
QString t = s.mid( 5, 4 ); // t == "pine"
Examples: network/mail/smtp.cpp, qmag/qmag.cpp, and themes/themes.cpp.
long a = 63;
QString str = QString::number( a, 16 ); // str == "3f"
QString str = QString::number( a, 16 ).upper(); // str == "3F"
See also setNum().
Examples: application/application.cpp, chart/chartform.cpp, fonts/simple-qfont-demo/viewer.cpp, helpviewer/helpwindow.cpp, mdi/application.cpp, regexptester/regexptester.cpp, and sql/overview/extract/main.cpp.
See also setNum().
See also setNum().
See also setNum().
See also setNum().
A convenience factory function that returns a string representation of the number n to the base base, which is 10 by default and must be between 2 and 36.
See also setNum().
Argument n is formatted according to the f format specified, which is g by default, and can be any 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 |
With 'e', 'E', and 'f', prec is the number of digits after the decimal point. With 'g' and 'G', prec is the maximum number of significant digits (trailing zeroes are omitted).
double d = 12.34;
QString ds = QString( "'E' format, precision 3, gives %1" )
.arg( d, 0, 'E', 3 );
// ds == "1.234E+001"
See also setNum().
Returns ascii(). Be sure to see the warnings documented in the ascii() function. 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 in operator!().
Returns ascii() as a std::string.
Warning: The function may cause an application to crash if a static C run-time is in use. This can happen in Microsoft Visual C++ if Qt is configured as single-threaded. A safe alternative is to call ascii() directly and construct a std::string manually.
Returns TRUE if this is a null string; otherwise returns FALSE.
QString name = getName();
if ( !name )
name = "Rodney";
Note that if you say
QString name = getName();
if ( name )
doSomethingWith(name);
It will call "operator const char*()", which is inefficent; you may wish to define the macro QT_NO_ASCII_CAST when writing code which you wish to remain Unicode-clean.
When you want the above semantics, use:
QString name = getName();
if ( !name.isNull() )
doSomethingWith(name);
See also isEmpty().
Appends str to the string and returns a reference to the string.
Appends str to the string and returns a reference to the string.
Appends str to the string and returns a reference to the string.
Appends c to the string and returns a reference to the string.
Appends c to the string and returns a reference to the string.
Sets the string to contain just the single character c.
Assigns a shallow copy of s to this string and returns a reference to this string. This is very fast because the string isn't actually copied.
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, then a null string is created.
See also isNull().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Makes a deep copy of s and returns a reference to the deep copy.
Assigns a deep copy of cstr, interpreted as a classic C string, to this string. Returns a reference to this string.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Sets the string to contain just the single character c.
Returns the character at index i, or QChar::null if i is beyond the length of the string.
If the QString is not const (i.e., const QString) or const& (i.e., const QString&), then the non-const overload of operator[] will be used instead.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
The function returns a reference to the character at index i. The resulting reference can then be assigned to, or used immediately, but it will become invalid once further modifications are made to the original string.
If i is beyond the length of the string then the string is expanded with QChar::nulls, so that the QCharRef references a valid (null) character in 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 will detach itself because of QString's copy-on-write semantics). You will get compilation errors if you try to use the result as anything but a QChar.
Inserts s at the beginning of the string and returns a reference to the string.
Equivalent to insert(0, s).
QString string = "42";
string.prepend( "The answer is " );
// string == "The answer is 42"
See also insert().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Inserts ch at the beginning of the string and returns a reference to the string.
Equivalent to insert(0, ch).
See also insert().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Inserts ch at the beginning of the string and returns a reference to the string.
Equivalent to insert(0, ch).
See also insert().
Inserts s at the beginning of the string and returns a reference to the string.
Equivalent to insert(0, s).
See also insert().
Inserts s at the beginning of the string and returns a reference to the string.
Equivalent to insert(0, s).
See also insert().
Inserts s at the beginning of the string and returns a reference to the string.
Equivalent to insert(0, s).
See also insert().
Returns the QChar at index i by reference, expanding the string with QChar::null if necessary. The resulting reference can be assigned to, or otherwise used immediately, but becomes invalid once furher modifications are made to the string.
QString string("ABCDEF");
QChar ch = string.ref( 3 ); // ch == 'D'
See also constref().
If index is beyond the length of the string, nothing happens. If index is within the string, but index + len is beyond the end of the string, the string is truncated at position index.
QString string( "Montreal" );
string.remove( 1, 4 ); // string == "Meal"
See also insert() and replace().
Removes every occurrence of str in the string. Returns a reference to the string.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
This is the same as replace(str, "", cs).
Removes every occurrence of the character c in the string. Returns a reference to the string.
This is the same as replace(c, "").
Removes every occurrence of the character c in the string. Returns a reference to the string.
This is the same as replace(c, "").
Removes every occurrence of str in the string. Returns a reference to the string.
Removes every occurrence of the regular expression rx in the string. Returns a reference to the string.
This is the same as replace(rx, "").
If index is beyond the length of the string, nothing is deleted and s is appended at the end of the string. If index is valid, but index + len is beyond the end of the string, the string is truncated at position index, then s is appended at the end.
QString string( "Say yes!" );
string = string.replace( 4, 3, "NO" );
// string == "Say NO!"
Warning: Qt 3.3.3 and earlier had different semantics for the case index >= length(), which contradicted the documentation. To avoid portability problems between Qt 3 versions and with Qt 4, we recommend that you never call the function with index >= length().
See also insert() and remove().
Examples: listviews/listviews.cpp, network/networkprotocol/nntp.cpp, qmag/qmag.cpp, and regexptester/regexptester.cpp.
Replaces len characters with slen characters of QChar data from s, starting at position index, and returns a reference to the string.
See also insert() and remove().
This is the same as replace(index, len, QString(c)).
This is the same as replace(index, len, QChar(c)).
Replaces every occurrence of the character c in the string with after. Returns a reference to the string.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString s = "a,b,c";
s.replace( QChar(','), " or " );
// s == "a or b or c"
Replaces every occurrence of the character c in the string with after. Returns a reference to the string.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Replaces every occurrence of the string before in the string with the string after. Returns a reference to the string.
If cs is TRUE (the default), the search is case sensitive; otherwise the search is case insensitive.
Example:
QString s = "Greek is Greek";
s.replace( "Greek", "English" );
// s == "English is English"
Replaces every occurrence of the regexp rx in the string with after. Returns a reference to the string. For example:
QString s = "banana";
s.replace( QRegExp("an"), "" );
// s == "ba"
For regexps 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 find(), findRev(), and QRegExp::cap().
Replaces every occurrence of c1 with the char c2. Returns a reference to the string.
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 big enough:
QString result;
int len = 0;
result.reserve(maxLen);
while (...) {
result[len++] = ... // fill part of the space
}
result.squeeze();
If maxLen is an underestimate, the worst that will happen is that the loop will slow down.
If it is not possible to allocate enough memory, the string remains unchanged.
See also capacity(), squeeze(), and setLength().
If len is greater than the length of the string then the whole string is returned.
QString string( "Pineapple" );
QString t = string.right( 5 ); // t == "apple"
See also left(), mid(), and isEmpty().
Example: fileiconview/qfileiconview.cpp.
If truncate is FALSE and the length of the string is more than width, then the returned string is a copy of the string.
If truncate is TRUE and the length of the string is more than width, then the resulting string is truncated at position width.
QString string( "apple" );
QString t = string.rightJustify( 8, '.' ); // t == "...apple"
See also leftJustify().
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 behaviour, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags.
QString csv( "forename,middlename,surname,phone" );
QString s = csv.section( ',', 2, 2 ); // s == "surname"
QString path( "/usr/local/bin/myapp" ); // First field is empty
QString s = path.section( '/', 3, 4 ); // s == "bin/myapp"
QString s = path.section( '/', 3, 3, SectionSkipEmpty ); // s == "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.
QString csv( "forename,middlename,surname,phone" );
QString s = csv.section( ',', -3, -2 ); // s == "middlename,surname"
QString path( "/usr/local/bin/myapp" ); // First field is empty
QString s = path.section( '/', -1 ); // s == "myapp"
See also QStringList::split().
Examples: chart/element.cpp and network/ftpclient/ftpmainwindow.ui.h.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
This function returns a section of the string.
This string is treated as a sequence of fields separated by the string, 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 behaviour, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags.
QString data( "forename**middlename**surname**phone" );
QString s = data.section( "**", 2, 2 ); // s == "surname"
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.
QString data( "forename**middlename**surname**phone" );
QString s = data.section( "**", -3, -2 ); // s == "middlename**surname"
See also QStringList::split().
This function returns a section of the string.
This string is treated as a sequence of fields separated by the regular expression, reg. 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 behaviour, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags.
QString line( "forename\tmiddlename surname \t \t phone" );
QRegExp sep( "\s+" );
QString s = line.section( sep, 2, 2 ); // s == "surname"
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.
QString line( "forename\tmiddlename surname \t \t phone" );
QRegExp sep( "\\s+" );
QString s = 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 QStringList::split() and simplifyWhiteSpace().
If str is 0 a null string is created. If str is "", an empty string is created.
See also isNull() and isEmpty().
Sets the character at position index to c and expands the string if necessary, filling with spaces.
This method is redundant in Qt 3.x, because operator[] will expand the string as necessary.
If str is 0 a null string is created. If str is "", an empty string is created.
See also isNull() and isEmpty().
See also reserve() and truncate().
The base is 10 by default and must be between 2 and 36.
QString string;
string = string.setNum( 1234 ); // string == "1234"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Sets the string to the printed value of n in base base and returns a reference to the string.
The base is 10 by default and must be between 2 and 36.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Sets the string to the printed value of n in base base and returns a reference to the string.
The base is 10 by default and must be between 2 and 36.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Sets the string to the printed value of n in base base and returns a reference to the string.
The base is 10 by default and must be between 2 and 36.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Sets the string to the printed value of n in base base and returns a reference to the string.
The base is 10 by default and must be between 2 and 36.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Sets the string to the printed value of n in base base and returns a reference to the string.
The base is 10 by default and must be between 2 and 36.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Sets the string to the printed value of n, formatted in format f with precision prec, and returns a reference to the string.
The format f can be 'f', 'F', 'e', 'E', 'g' or 'G'. See arg() for an explanation of the formats.
Sets the string to the printed value of n, formatted in format f with precision prec, and returns a reference to the string.
The format f can be 'f', 'F', 'e', 'E', 'g' or 'G'. See arg() for an explanation of the formats.
See also setLatin1() and isNull().
If unicode_as_ushorts is 0, nothing is copied, but the string is still resized to len. If len is zero, the string becomes a null string.
See also setLatin1() and isNull().
Whitespace means any character for which QChar::isSpace() returns TRUE. This includes Unicode characters with decimal values 9 (TAB), 10 (LF), 11 (VT), 12 (FF), 13 (CR), and 32 (Space).
QString string = " lots\t of\nwhite space ";
QString t = string.simplifyWhiteSpace();
// t == "lots of white space"
See also stripWhiteSpace().
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 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.
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::ucs2()).
See also arg().
Examples: dclock/dclock.cpp, forever/forever.cpp, layout/layout.cpp, qmag/qmag.cpp, scrollview/scrollview.cpp, tooltip/tooltip.cpp, and xform/xform.cpp.
See also capacity() and reserve().
If cs is TRUE (the 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().
Whitespace means any character for which QChar::isSpace() returns TRUE. This includes Unicode characters with decimal values 9 (TAB), 10 (LF), 11 (VT), 12 (FF), 13 (CR) and 32 (Space), and may also include other Unicode characters.
QString string = " white space ";
QString s = string.stripWhiteSpace(); // s == "white space"
See also simplifyWhiteSpace().
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
QString string( "1234.56" );
double a = string.toDouble(); // a == 1234.56
The string-to-number functions:
bool ok;
double d;
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, these functions do not handle thousands group separators. If you need to convert such numbers, use the corresponding function in QLocale.
bool ok;
QLocale::setDefault(QLocale::C);
double d = QString( "1,234,567.89" ).toDouble(&ok); // ok == false
Warning: If the string contains trailing whitespace this function will fail, and set *ok to false if ok is not 0. Leading whitespace is ignored.
See also number(), QLocale::setDefault(), QLocale::toDouble(), and stripWhiteSpace().
Returns 0.0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
For information on how string-to-number functions in QString handle localized input, see toDouble().
Warning: If the string contains trailing whitespace this function will fail, settings *ok to false if ok is not 0. Leading whitespace is ignored.
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
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
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
Returns 0 if the conversion fails.
If ok is not 0: if a conversion error occurs, *ok is set to FALSE; otherwise *ok is set to TRUE.
Leading and trailing whitespace is ignored by this function.
For information on how string-to-number functions in QString handle localized input, see toDouble().
See also number().
QString s = "truncate me";
s.truncate( 5 ); // s == "trunc"
See also setLength().
Example: network/mail/smtp.cpp.
The result remains valid so long as one unmodified copy of the source string exists.
Example: dotnet/wrapper/lib/tools.cpp.
Returns the Unicode representation of the string. The result remains valid until the string is modified.
QString string( "TeXt" );
str = string.upper(); // t == "TEXT"
See also lower().
Examples: scribble/scribble.cpp and sql/overview/custom1/main.cpp.
See QTextCodec for more diverse coding/decoding of Unicode strings.
See also fromUtf8(), ascii(), latin1(), and local8Bit().
Example: network/archivesearch/archivedialog.ui.h.
Returns TRUE if s1 is not equal to s2; otherwise returns FALSE. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) != 0.
See also isNull() and isEmpty().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is not equal to s2; otherwise returns FALSE. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) != 0.
See also isNull() and isEmpty().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is not equal to s2; otherwise returns FALSE. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) != 0.
See also isNull() and isEmpty().
Returns a string which is the result of concatenating the string s1 and the string s2.
Equivalent to s1.append(s2).
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns a string which is the result of concatenating the string s1 and character s2.
Equivalent to s1.append(s2).
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns a string which is the result of concatenating the character s1 and string s2.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns a string which is the result of concatenating the string s and character c.
Equivalent to s.append(c).
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns a string which is the result of concatenating the character c and string s.
Equivalent to s.prepend(c).
Returns TRUE if s1 is lexically less than s2; otherwise returns FALSE. The comparison is case sensitive.
Equivalent to compare(s1, s2) < 0.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is lexically less than s2; otherwise returns FALSE. The comparison is case sensitive.
Equivalent to compare(s1, s2) < 0.
Writes the string str to the stream s.
See also Format of the QDataStream operators
Returns TRUE if s1 is lexically less than or equal to s2; otherwise returns FALSE. The comparison is case sensitive. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1,s2) <= 0.
See also isNull() and isEmpty().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is lexically less than or equal to s2; otherwise returns FALSE. The comparison is case sensitive. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) <= 0.
See also isNull() and isEmpty().
Returns TRUE if s1 is equal to s2; otherwise returns FALSE. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) == 0.
See also isNull() and isEmpty().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is equal to s2; otherwise returns FALSE. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) == 0.
See also isNull() and isEmpty().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is equal to s2; otherwise returns FALSE. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) == 0.
See also isNull() and isEmpty().
Returns TRUE if s1 is lexically greater than s2; otherwise returns FALSE. The comparison is case sensitive.
Equivalent to compare(s1, s2) > 0.
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is lexically greater than s2; otherwise returns FALSE. The comparison is case sensitive.
Equivalent to compare(s1, s2) > 0.
Returns TRUE if s1 is lexically greater than or equal to s2; otherwise returns FALSE. The comparison is case sensitive. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) >= 0.
See also isNull() and isEmpty().
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns TRUE if s1 is lexically greater than or equal to s2; otherwise returns FALSE. The comparison is case sensitive. Note that a null string is not equal to a not-null empty string.
Equivalent to compare(s1, s2) >= 0.
See also isNull() and isEmpty().
Reads a string from the stream s into string str.
See also Format of the QDataStream operators
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