QString Class

Member Function Documentation

template <typename Args> QString QString::arg(Args &&... args) const

Replaces occurrences of %N in this string with the corresponding argument from args. The arguments are not positional: the first of the args replaces the %N with the lowest N (all of them), the second of the args the %N with the next-lowest N etc.

Args can consist of anything that implicitly converts to QString, QStringView or QLatin1StringView.

In addition, the following types are also supported: QChar, QLatin1Char.

See also QString::arg().

Splits the string into substring views wherever sep occurs, and returns a lazy sequence of those strings.

Equivalent to

return QStringTokenizer{std::forward<Needle>(sep), flags...};

except it works without C++17 Class Template Argument Deduction (CTAD) enabled in the compiler.

See QStringTokenizer for how sep and flags interact to form the result.

QStringTokenizer result = sv.tokenize(sep);

(without template arguments). If you can't use C++17 CTAD, you must store the return value only in auto variables:

auto result = sv.tokenize(sep);

This is because the template arguments of QStringTokenizer have a very subtle dependency on the specific tokenize() overload from which they are returned, and they don't usually correspond to the type used for the separator.

This function was introduced in Qt 6.0.

See also QStringTokenizer and qTokenize().

[constexpr] QString::QString()

Constructs a null string. Null strings are also considered empty.

See also isEmpty(), isNull(), and Distinction Between Null and Empty Strings.

[explicit] QString::QString(const QChar *unicode, qsizetype size = -1)

Constructs a string initialized with the first size characters of the QChar array unicode.

If unicode is 0, a null string is constructed.

If size is negative, unicode is assumed to point to a \0'-terminated array and its length is determined dynamically. The terminating null character is not considered part of the string.

QString makes a deep copy of the string data. The unicode data is copied as is and the Byte Order Mark is preserved if present.

See also fromRawData().

QString::QString(QChar ch)

Constructs a string of size 1 containing the character ch.

QString::QString(qsizetype size, QChar ch)

Constructs a string of the given size with every character set to ch.

See also fill().

QString::QString(QLatin1StringView str)

Constructs a copy of the Latin-1 string viewed by str.

See also fromLatin1().

[since 6.1] QString::QString(const char8_t *str)

Constructs a string initialized with the UTF-8 string str. The given const char8_t pointer is converted to Unicode using the fromUtf8() function.

This function was introduced in Qt 6.1.

See also fromLatin1(), fromLocal8Bit(), and fromUtf8().

QString::QString(const char *str)

Constructs a string initialized with the 8-bit string str. The given const char pointer is converted to Unicode using the fromUtf8() function.

You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

See also fromLatin1(), fromLocal8Bit(), and fromUtf8().

QString::QString(const QByteArray &ba)

Constructs a string initialized with the byte array ba. The given byte array is converted to Unicode using fromUtf8().

You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

See also fromLatin1(), fromLocal8Bit(), and fromUtf8().

QString::QString(const QString &other)

Constructs a copy of other.

This operation takes constant time, because QString is implicitly shared. This makes returning a QString from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes linear time.

See also operator=().

QString::QString(QString &&other)

Move-constructs a QString instance, making it point at the same object that other was pointing to.

QString::~QString()

Destroys the string.

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

Appends the string str onto the end of this string.

Example:

QString x = "free";
QString y = "dom";

x.append(y);
// x == "freedom"

This is the same as using the insert() function:

x.insert(x.size(), y);

The append() function is typically very fast (constant time), because QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.

See also operator+=(), prepend(), and insert().

QString &QString::append(QChar ch)

This function overloads append().

Appends the character ch to this string.

QString &QString::append(const QChar *str, qsizetype len)

This function overloads append().

Appends len characters from the QChar array str to this string.

[since 6.0] QString &QString::append(QStringView v)

This function overloads append().

Appends the given string view v to this string and returns the result.

This function was introduced in Qt 6.0.

QString &QString::append(QLatin1StringView str)

This function overloads append().

Appends the Latin-1 string viewed by str to this string.

[since 6.5] QString &QString::append(QUtf8StringView str)

This function overloads append().

Appends the UTF-8 string view str to this string.

This function was introduced in Qt 6.5.

QString &QString::append(const char *str)

This function overloads append().

Appends the string str to this string. The given const char pointer is converted to Unicode using the fromUtf8() function.

You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

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

This function overloads append().

Appends the byte array ba to this string. The given byte array is converted to Unicode using the fromUtf8() function.

You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

QString QString::arg(const QString &a, int fieldWidth = 0, QChar fillChar = u' ') const

Returns a copy of this string with the lowest numbered place marker replaced by string a, i.e., %1, %2, ..., %99.

fieldWidth specifies the minimum amount of space that argument a shall occupy. If a requires less space than fieldWidth, it is padded to fieldWidth with character fillChar. A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.

This example shows how we might create a status string for reporting progress while processing a list of files:

QString i;           // current file's number
QString total;       // number of files to process
QString fileName;    // current file's name

QString status = QString("Processing file %1 of %2: %3")
                .arg(i).arg(total).arg(fileName);

First, arg(i) replaces %1. Then arg(total) replaces %2. Finally, arg(fileName) replaces %3.

One advantage of using arg() over asprintf() is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest numbered unreplaced place marker, no matter where it appears. Also, if place marker %i appears more than once in the string, the arg() replaces all of them.

If there is no unreplaced place marker remaining, a warning message is output and the result is undefined. Place marker numbers must be in the range 1 to 99.

QString QString::arg(qlonglong a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

See also Number Formats.

QString QString::arg(qulonglong a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

The base argument specifies the base to use when converting the integer a into a string. base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

See also Number Formats.

QString QString::arg(long a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

The a argument is expressed in the given base, which is 10 by default and must be between 2 and 36.

The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a. The conversion uses the default locale. The default locale is determined from the system's locale settings at application startup. It can be changed using QLocale::setDefault(). The 'L' flag is ignored if base is not 10.

QString str;
str = QString("Decimal 63 is %1 in hexadecimal")
        .arg(63, 0, 16);
// str == "Decimal 63 is 3f in hexadecimal"

QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates));
str = QString("%1 %L2 %L3")
        .arg(12345)
        .arg(12345)
        .arg(12345, 0, 16);
// str == "12345 12,345 3039"

See also Number Formats.

QString QString::arg(ulong a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

The base argument specifies the base to use when converting the integer a to a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

See also Number Formats.

QString QString::arg(int a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

The a argument is expressed in base base, which is 10 by default and must be between 2 and 36. For bases other than 10, a is treated as an unsigned integer.

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a. The conversion uses the default locale, set by QLocale::setDefault(). If no default locale was specified, the system locale is used. The 'L' flag is ignored if base is not 10.

QString str;
str = QString("Decimal 63 is %1 in hexadecimal")
        .arg(63, 0, 16);
// str == "Decimal 63 is 3f in hexadecimal"

QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates));
str = QString("%1 %L2 %L3")
        .arg(12345)
        .arg(12345)
        .arg(12345, 0, 16);
// str == "12345 12,345 3039"

See also Number Formats.

QString QString::arg(uint a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36.

See also Number Formats.

QString QString::arg(short a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

See also Number Formats.

QString QString::arg(ushort a, int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

This function overloads arg().

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

See also Number Formats.

QString QString::arg(double a, int fieldWidth = 0, char format = 'g', int precision = -1, QChar fillChar = u' ') const

This function overloads arg().

Argument a is formatted according to the specified format and precision. See Floating-point Formats for details.

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar. A positive value produces right-aligned text; a negative value produces left-aligned text.

double d = 12.34;
QString str = QString("delta: %1").arg(d, 0, 'E', 3);
// str == "delta: 1.234E+01"

See also QLocale::toString(), QLocale::FloatingPointPrecisionOption, and Number Formats.

QString QString::arg(char a, int fieldWidth = 0, QChar fillChar = u' ') const

This function overloads arg().

The a argument is interpreted as a Latin-1 character.

QString QString::arg(QChar a, int fieldWidth = 0, QChar fillChar = u' ') const

This function overloads arg().

QString QString::arg(QStringView a, int fieldWidth = 0, QChar fillChar = u' ') const

This is an overloaded function.

Returns a copy of this string with the lowest-numbered place-marker replaced by string a, i.e., %1, %2, ..., %99.

fieldWidth specifies the minimum amount of space that a shall occupy. If a requires less space than fieldWidth, it is padded to fieldWidth with character fillChar. A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.

This example shows how we might create a status string for reporting progress while processing a list of files:

int i;                // current file's number
int total;            // number of files to process
QStringView fileName; // current file's name

QString status = QString("Processing file %1 of %2: %3")
                .arg(i).arg(total).arg(fileName);

First, arg(i) replaces %1. Then arg(total) replaces %2. Finally, arg(fileName) replaces %3.

One advantage of using arg() over asprintf() is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest-numbered unreplaced place-marker, no matter where it appears. Also, if place-marker %i appears more than once in the string, arg() replaces all of them.

If there is no unreplaced place-marker remaining, a warning message is printed and the result is undefined. Place-marker numbers must be in the range 1 to 99.

QString QString::arg(QLatin1StringView a, int fieldWidth = 0, QChar fillChar = u' ') const

This is an overloaded function.

Returns a copy of this string with the lowest-numbered place-marker replaced by the Latin-1 string viewed by a, i.e., %1, %2, ..., %99.

fieldWidth specifies the minimum amount of space that a shall occupy. If a requires less space than fieldWidth, it is padded to fieldWidth with character fillChar. A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.

One advantage of using arg() over asprintf() is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest-numbered unreplaced place-marker, no matter where it appears. Also, if place-marker %i appears more than once in the string, arg() replaces all of them.

If there is no unreplaced place-marker remaining, a warning message is printed and the result is undefined. Place-marker numbers must be in the range 1 to 99.

[static] QString QString::asprintf(const char *cformat, ...)

Safely builds a formatted string from the format string cformat and an arbitrary list of arguments.

The format string supports the conversion specifiers, length modifiers, and flags provided by printf() in the standard C++ library. The cformat string and %s arguments must be UTF-8 encoded.

QString result;
QTextStream(&result) << "pi = " << 3.14;
// result == "pi = 3.14"

For translations, especially if the strings contains more than one escape sequence, you should consider using the arg() function instead. This allows the order of the replacements to be controlled by the translator.

See also arg().

const QChar QString::at(qsizetype position) const

Returns the character at the given index position in the string.

The position must be a valid index position in the string (i.e., 0 <= position < size()).

See also operator[]().

QChar QString::back() const

Returns the last character in the string. Same as at(size() - 1).

This function is provided for STL compatibility.

See also front(), at(), and operator[]().

QChar &QString::back()

Returns a reference to the last character in the string. Same as operator[](size() - 1).

This function is provided for STL compatibility.

See also front(), at(), and operator[]().

QString::iterator QString::begin()

Returns an STL-style iterator pointing to the first character in the string.

See also constBegin() and end().

QString::const_iterator QString::begin() const

This function overloads begin().

qsizetype QString::capacity() const

Returns the maximum number of characters that can be stored in the string without forcing a reallocation.

The sole purpose of this function is to provide a means of fine tuning QString's memory usage. In general, you will rarely ever need to call this function. If you want to know how many characters are in the string, call size().

See also reserve() and squeeze().

QString::const_iterator QString::cbegin() const

Returns a const STL-style iterator pointing to the first character in the string.

See also begin() and cend().

QString::const_iterator QString::cend() const

Returns a const STL-style iterator pointing just after the last character in the string.

See also cbegin() and end().

void QString::chop(qsizetype n)

Removes n characters from the end of the string.

If n is greater than or equal to size(), the result is an empty string; if n is negative, it is equivalent to passing zero.

Example:

QString str("LOGOUT\r\n");
str.chop(2);
// str == "LOGOUT"

If you want to remove characters from the beginning of the string, use remove() instead.

See also truncate(), resize(), remove(), and QStringView::chop().

QString QString::chopped(qsizetype len) const

Returns a string that contains the size() - len leftmost characters of this string.

See also endsWith(), first(), last(), sliced(), chop(), and truncate().

void QString::clear()

Clears the contents of the string and makes it null.

See also resize() and isNull().

[static] int QString::compare(const QString &s1, const QString &s2, Qt::CaseSensitivity cs = Qt::CaseSensitive)

Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2.

If cs is Qt::CaseSensitive (the default), the comparison is case-sensitive; otherwise the comparison is case-insensitive.

Case sensitive comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-visible strings with localeAwareCompare().

int x = QString::compare("aUtO", "AuTo", Qt::CaseInsensitive);  // x == 0
int y = QString::compare("auto", "Car", Qt::CaseSensitive);     // y > 0
int z = QString::compare("auto", "Car", Qt::CaseInsensitive);   // z < 0

See also operator==(), operator<(), operator>(), and Comparing Strings.

int QString::compare(const QString &other, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads compare().

Lexically compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.

Same as compare(*this, other, cs).

int QString::compare(QLatin1StringView other, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads compare().

Same as compare(*this, other, cs).

int QString::compare(QStringView s, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads compare().

Performs a comparison of this with s, using the case sensitivity setting cs.

int QString::compare(QChar ch, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads compare().

Performs a comparison of this with ch, using the case sensitivity setting cs.

[static] int QString::compare(const QString &s1, QLatin1StringView s2, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads compare().

Performs a comparison of s1 and s2, using the case sensitivity setting cs.

[static] int QString::compare(QLatin1StringView s1, const QString &s2, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads compare().

Performs a comparison of s1 and s2, using the case sensitivity setting cs.

[static] int QString::compare(const QString &s1, QStringView s2, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads compare().

[static] int QString::compare(QStringView s1, const QString &s2, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads compare().

QString::const_iterator QString::constBegin() const

Returns a const STL-style iterator pointing to the first character in the string.

See also begin() and constEnd().

const QChar *QString::constData() const

Returns a pointer to the data stored in the QString. The pointer can be used to access the characters that compose the string.

Note that the pointer remains valid only as long as the string is not modified.

See also data(), operator[](), and fromRawData().

QString::const_iterator QString::constEnd() const

Returns a const STL-style iterator pointing just after the last character in the string.

See also constBegin() and end().

bool QString::contains(const QString &str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns true if this string contains an occurrence of the string str; otherwise returns false.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString str = "Peter Pan";
str.contains("peter", Qt::CaseInsensitive);    // returns true

See also indexOf() and count().

bool QString::contains(QChar ch, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads contains().

Returns true if this string contains an occurrence of the character ch; otherwise returns false.

bool QString::contains(QLatin1StringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads contains().

Returns true if this string contains an occurrence of the latin-1 string str; otherwise returns false.

bool QString::contains(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads contains().

Returns true if this string contains an occurrence of the string view str; otherwise returns false.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

See also indexOf() and count().

bool QString::contains(const QRegularExpression &re, QRegularExpressionMatch *rmatch = nullptr) const

Returns true if the regular expression re matches somewhere in this string; otherwise returns false.

If the match is successful and rmatch is not nullptr, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch.

See also QRegularExpression::match().

qsizetype QString::count(const QString &str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the number of (potentially overlapping) occurrences of the string str in this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

See also contains() and indexOf().

qsizetype QString::count(QChar ch, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads count().

Returns the number of occurrences of character ch in the string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

See also contains() and indexOf().

[since 6.0] qsizetype QString::count(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads count().

Returns the number of (potentially overlapping) occurrences of the string view str in this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

This function was introduced in Qt 6.0.

See also contains() and indexOf().

qsizetype QString::count(const QRegularExpression &re) const

This function overloads count().

Returns the number of times the regular expression re matches in the string.

For historical reasons, this function counts overlapping matches, so in the example below, there are four instances of "ana" or "ama":

QString str = "banana and panama";
str.count(QRegularExpression("a[nm]a"));    // returns 4

This behavior is different from simply iterating over the matches in the string using QRegularExpressionMatchIterator.

See also QRegularExpression::globalMatch().

QString::const_reverse_iterator QString::crbegin() const

Returns a const STL-style reverse iterator pointing to the first character in the string, in reverse order.

See also begin(), rbegin(), and rend().

QString::const_reverse_iterator QString::crend() const

Returns a const STL-style reverse iterator pointing just after the last character in the string, in reverse order.

See also end(), rend(), and rbegin().

QChar *QString::data()

Returns a pointer to the data stored in the QString. The pointer can be used to access and modify the characters that compose the string.

Unlike constData() and unicode(), the returned data is always '\0'-terminated.

Example:

QString str = "Hello world";
QChar *data = str.data();
while (!data->isNull()) {
    qDebug() << data->unicode();
    ++data;
}

Note that the pointer remains valid only as long as the string is not modified by other means. For read-only access, constData() is faster because it never causes a deep copy to occur.

See also constData() and operator[]().

const QChar *QString::data() const

This is an overloaded function.

See also fromRawData().

QString::iterator QString::end()

Returns an STL-style iterator pointing just after the last character in the string.

See also begin() and constEnd().

QString::const_iterator QString::end() const

This function overloads end().

bool QString::endsWith(const QString &s, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns true if the string ends with s; otherwise returns false.

If cs is Qt::CaseSensitive (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().

bool QString::endsWith(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads endsWith().

Returns true if the string ends with the string view str; otherwise returns false.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

See also startsWith().

bool QString::endsWith(QLatin1StringView s, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads endsWith().

bool QString::endsWith(QChar c, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns true if the string ends with c; otherwise returns false.

This function overloads endsWith().

[since 6.1] QString::iterator QString::erase(QString::const_iterator first, QString::const_iterator last)

Removes from the string the characters in the half-open range [ first , last ). Returns an iterator to the character immediately after the last erased character (i.e. the character referred to by last before the erase).

This function was introduced in Qt 6.1.

[since 6.5] QString::iterator QString::erase(QString::const_iterator it)

Removes the character denoted by it from the string. Returns an iterator to the character immediately after the erased character.

QString c = "abcdefg";
auto it = c.erase(c.cbegin()); // c is now "bcdefg"; "it" points to "b"

This function was introduced in Qt 6.5.

QString &QString::fill(QChar ch, qsizetype size = -1)

Sets every character in the string to character ch. If size is different from -1 (default), the string is resized to size beforehand.

Example:

QString str = "Berlin";
str.fill('z');
// str == "zzzzzz"

str.fill('A', 2);
// str == "AA"

See also resize().

[since 6.0] QString QString::first(qsizetype n) const

Returns a string that contains the first n characters of this string.

QString x = "Pineapple";
QString y = x.first(4);      // y == "Pine"

This function was introduced in Qt 6.0.

See also last(), sliced(), startsWith(), chopped(), chop(), and truncate().

[static] QString QString::fromCFString(CFStringRef string)

Constructs a new QString containing a copy of the string CFString.

[static] QString QString::fromLatin1(const char *str, qsizetype size)

Returns a QString initialized with the first size characters of the Latin-1 string str.

If size is -1, strlen(str) is used instead.

See also toLatin1(), fromUtf8(), and fromLocal8Bit().

[static, since 6.0] QString QString::fromLatin1(QByteArrayView str)

This is an overloaded function.

Returns a QString initialized with the Latin-1 string str.

This function was introduced in Qt 6.0.

[static] QString QString::fromLatin1(const QByteArray &str)

This is an overloaded function.

Returns a QString initialized with the Latin-1 string str.

[static] QString QString::fromLocal8Bit(const char *str, qsizetype size)

Returns a QString initialized with the first size characters of the 8-bit string str.

If size is -1, strlen(str) is used instead.

On Unix systems this is equivalent to fromUtf8(), on Windows the systems current code page is being used.

See also toLocal8Bit(), fromLatin1(), and fromUtf8().

[static, since 6.0] QString QString::fromLocal8Bit(QByteArrayView str)

This is an overloaded function.

Returns a QString initialized with the 8-bit string str.

This function was introduced in Qt 6.0.

[static] QString QString::fromLocal8Bit(const QByteArray &str)

This is an overloaded function.

Returns a QString initialized with the 8-bit string str.

[static] QString QString::fromNSString(const NSString *string)

Constructs a new QString containing a copy of the string NSString.

[static] QString QString::fromRawData(const QChar *unicode, qsizetype size)

Constructs a QString that uses the first size Unicode characters in the array unicode. The data in unicode is not copied. The caller must be able to guarantee that unicode will not be deleted or modified as long as the QString (or an unmodified copy of it) exists.

Any attempts to modify the QString or copies of it will cause it to create a deep copy of the data, ensuring that the raw data isn't modified.

Here is an example of how we can use a QRegularExpression on raw data in memory without requiring to copy the data into a QString:

QRegularExpression pattern("\u00A4");
static const QChar unicode[] = {
        0x005A, 0x007F, 0x00A4, 0x0060,
        0x1009, 0x0020, 0x0020};
qsizetype size = sizeof(unicode) / sizeof(QChar);

QString str = QString::fromRawData(unicode, size);
if (str.contains(pattern) {
    // ...
}

See also fromUtf16() and setRawData().

[static] QString QString::fromStdString(const std::string &str)

Returns a copy of the str string. The given string is converted to Unicode using the fromUtf8() function.

See also fromLatin1(), fromLocal8Bit(), fromUtf8(), and QByteArray::fromStdString().

[static] QString QString::fromStdU16String(const std::u16string &str)

Returns a copy of the str string. The given string is assumed to be encoded in UTF-16.

See also fromUtf16(), fromStdWString(), and fromStdU32String().

[static] QString QString::fromStdU32String(const std::u32string &str)

Returns a copy of the str string. The given string is assumed to be encoded in UCS-4.

See also fromUcs4(), fromStdWString(), and fromStdU16String().

[static] QString QString::fromStdWString(const std::wstring &str)

Returns a copy of the str string. The given string is assumed to be encoded in utf16 if the size of wchar_t is 2 bytes (e.g. on windows) and ucs4 if the size of wchar_t is 4 bytes (most Unix systems).

See also fromUtf16(), fromLatin1(), fromLocal8Bit(), fromUtf8(), fromUcs4(), fromStdU16String(), and fromStdU32String().

[static] QString QString::fromUcs4(const char32_t *unicode, qsizetype size = -1)

Returns a QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UCS-4 encoded).

If size is -1 (default), unicode must be \0'-terminated.

See also toUcs4(), fromUtf16(), utf16(), setUtf16(), fromWCharArray(), and fromStdU32String().

[static] QString QString::fromUtf8(const char *str, qsizetype size)

Returns a QString initialized with the first size bytes of the UTF-8 string str.

If size is -1, strlen(str) is used instead.

UTF-8 is a Unicode codec and can represent all characters in a Unicode string like QString. However, invalid sequences are possible with UTF-8 and, if any such are found, they will be replaced with one or more "replacement characters", or suppressed. These include non-Unicode sequences, non-characters, overlong sequences or surrogate codepoints encoded into UTF-8.

This function can be used to process incoming data incrementally as long as all UTF-8 characters are terminated within the incoming data. Any unterminated characters at the end of the string will be replaced or suppressed. In order to do stateful decoding, please use QStringDecoder.

See also toUtf8(), fromLatin1(), and fromLocal8Bit().

[static, since 6.0] QString QString::fromUtf8(QByteArrayView str)

This is an overloaded function.

Returns a QString initialized with the UTF-8 string str.

This function was introduced in Qt 6.0.

[static] QString QString::fromUtf8(const QByteArray &str)

This is an overloaded function.

Returns a QString initialized with the UTF-8 string str.

[static, since 6.1] QString QString::fromUtf8(const char8_t *str)

This is an overloaded function.

This overload is only available when compiling in C++20 mode.

This function was introduced in Qt 6.1.

[static, since 6.0] QString QString::fromUtf8(const char8_t *str, qsizetype size)

This is an overloaded function.

This overload is only available when compiling in C++20 mode.

This function was introduced in Qt 6.0.

[static] QString QString::fromUtf16(const char16_t *unicode, qsizetype size = -1)

Returns a QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UTF-16 encoded).

If size is -1 (default), unicode must be \0'-terminated.

This function checks for a Byte Order Mark (BOM). If it is missing, host byte order is assumed.

This function is slow compared to the other Unicode conversions. Use QString(const QChar *, qsizetype) or QString(const QChar *) if possible.

QString makes a deep copy of the Unicode data.

See also utf16(), setUtf16(), and fromStdU16String().

[static] QString QString::fromWCharArray(const wchar_t *string, qsizetype size = -1)

Returns a copy of the string, where the encoding of string depends on the size of wchar. If wchar is 4 bytes, the string is interpreted as UCS-4, if wchar is 2 bytes it is interpreted as UTF-16.

If size is -1 (default), the string must be '\0'-terminated.

See also fromUtf16(), fromLatin1(), fromLocal8Bit(), fromUtf8(), fromUcs4(), and fromStdWString().

QChar QString::front() const

Returns the first character in the string. Same as at(0).

This function is provided for STL compatibility.

See also back(), at(), and operator[]().

QChar &QString::front()

Returns a reference to the first character in the string. Same as operator[](0).

This function is provided for STL compatibility.

See also back(), at(), and operator[]().

qsizetype QString::indexOf(QLatin1StringView str, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the first occurrence of the Latin-1 string viewed by str in this string, searching forward from index position from. Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString x = "sticky question";
QString y = "sti";
x.indexOf(y);               // returns 0
x.indexOf(y, 1);            // returns 10
x.indexOf(y, 10);           // returns 10
x.indexOf(y, 11);           // returns -1

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

See also lastIndexOf(), contains(), and count().

qsizetype QString::indexOf(QChar ch, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads indexOf().

Returns the index position of the first occurrence of the character ch in this string, searching forward from index position from. Returns -1 if ch is not found.

qsizetype QString::indexOf(const QString &str, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the first occurrence of the string str in this string, searching forward from index position from. Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString x = "sticky question";
QString y = "sti";
x.indexOf(y);               // returns 0
x.indexOf(y, 1);            // returns 10
x.indexOf(y, 10);           // returns 10
x.indexOf(y, 11);           // returns -1

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

See also lastIndexOf(), contains(), and count().

qsizetype QString::indexOf(QStringView str, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads indexOf().

Returns the index position of the first occurrence of the string view str in this string, searching forward from index position from. Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

See also QStringView::indexOf(), lastIndexOf(), contains(), and count().

qsizetype QString::indexOf(const QRegularExpression &re, qsizetype from = 0, QRegularExpressionMatch *rmatch = nullptr) const

Returns the index position of the first match of the regular expression re in the string, searching forward from index position from. Returns -1 if re didn't match anywhere.

If the match is successful and rmatch is not nullptr, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch.

Example:

QString str = "the minimum";
str.indexOf(QRegularExpression("m[aeiou]"), 0);       // returns 4

QString str = "the minimum";
QRegularExpressionMatch match;
str.indexOf(QRegularExpression("m[aeiou]"), 0, &match);       // returns 4
// match.captured() == mi

QString &QString::insert(qsizetype position, const QString &str)

Inserts the string str at the given index position and returns a reference to this string.

Example:

QString str = "Meal";
str.insert(1, QString("ontr"));
// str == "Montreal"

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by str.

See also append(), prepend(), replace(), and remove().

QString &QString::insert(qsizetype position, QChar ch)

This function overloads insert().

Inserts ch at the given index position in the string.

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by ch.

QString &QString::insert(qsizetype position, const QChar *unicode, qsizetype size)

This function overloads insert().

Inserts the first size characters of the QChar array unicode at the given index position in the string.

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by size characters of the QChar array unicode.

[since 6.0] QString &QString::insert(qsizetype position, QStringView str)

This function overloads insert().

Inserts the string view str at the given index position and returns a reference to this string.

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by str.

This function was introduced in Qt 6.0.

QString &QString::insert(qsizetype position, QLatin1StringView str)

This function overloads insert().

Inserts the Latin-1 string viewed by str at the given index position.

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by str.

[since 6.5] QString &QString::insert(qsizetype position, QUtf8StringView str)

This function overloads insert().

Inserts the UTF-8 string view str at the given index position.

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by str.

This function was introduced in Qt 6.5.

QString &QString::insert(qsizetype position, const char *str)

This function overloads insert().

Inserts the C string str at the given index position and returns a reference to this string.

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by str.

This function is not available when QT_NO_CAST_FROM_ASCII is defined.

QString &QString::insert(qsizetype position, const QByteArray &str)

This function overloads insert().

Interprets the contents of str as UTF-8, inserts the Unicode string it encodes at the given index position and returns a reference to this string.

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position, followed by str.

This function is not available when QT_NO_CAST_FROM_ASCII is defined.

bool QString::isEmpty() const

Returns true if the string has no characters; otherwise returns false.

Example:

QString().isEmpty();            // returns true
QString("").isEmpty();          // returns true
QString("x").isEmpty();         // returns false
QString("abc").isEmpty();       // returns false

See also size().

bool QString::isLower() const

Returns true if the string is lowercase, that is, it's identical to its toLower() folding.

Note that this does not mean that the string does not contain uppercase letters (some uppercase letters do not have a lowercase folding; they are left unchanged by toLower()). For more information, refer to the Unicode standard, section 3.13.

See also QChar::toLower() and isUpper().

bool QString::isNull() const

Returns true if this string is null; otherwise returns false.

Example:

QString().isNull();             // returns true
QString("").isNull();           // returns false
QString("abc").isNull();        // returns false

Qt makes a distinction between null strings and empty strings for historical reasons. For most applications, what matters is whether or not a string contains any data, and this can be determined using the isEmpty() function.

See also isEmpty().

bool QString::isRightToLeft() const

Returns true if the string is read right to left.

See also QStringView::isRightToLeft().

bool QString::isUpper() const

Returns true if the string is uppercase, that is, it's identical to its toUpper() folding.

Note that this does not mean that the string does not contain lowercase letters (some lowercase letters do not have a uppercase folding; they are left unchanged by toUpper()). For more information, refer to the Unicode standard, section 3.13.

See also QChar::toUpper() and isLower().

bool QString::isValidUtf16() const

Returns true if the string contains valid UTF-16 encoded data, or false otherwise.

Note that this function does not perform any special validation of the data; it merely checks if it can be successfully decoded from UTF-16. The data is assumed to be in host byte order; the presence of a BOM is meaningless.

See also QStringView::isValidUtf16().

[since 6.0] QString QString::last(qsizetype n) const

Returns the string that contains the last n characters of this string.

QString x = "Pineapple";
QString y = x.last(5);      // y == "apple"

This function was introduced in Qt 6.0.

See also first(), sliced(), endsWith(), chopped(), chop(), and truncate().

qsizetype QString::lastIndexOf(const QString &str, qsizetype from, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the last occurrence of the string str in this string, searching backward from index position from.

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1

See also indexOf(), contains(), and count().

[since 6.3] qsizetype QString::lastIndexOf(QChar c, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

This function was introduced in Qt 6.3.

qsizetype QString::lastIndexOf(QChar ch, qsizetype from, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the character ch in this string, searching backward from index position from.

[since 6.2] qsizetype QString::lastIndexOf(QLatin1StringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the string str in this string. Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1

This function was introduced in Qt 6.2.

See also indexOf(), contains(), and count().

qsizetype QString::lastIndexOf(QLatin1StringView str, qsizetype from, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the Latin-1 string viewed by str in this string, searching backward from index position from.

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1

See also indexOf(), contains(), and count().

[since 6.2] qsizetype QString::lastIndexOf(const QString &str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the string str in this string. Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1

This function was introduced in Qt 6.2.

See also indexOf(), contains(), and count().

[since 6.2] qsizetype QString::lastIndexOf(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the string view str in this string. Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

This function was introduced in Qt 6.2.

See also indexOf(), contains(), and count().

qsizetype QString::lastIndexOf(QStringView str, qsizetype from, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the string view str in this string, searching backward from index position from.

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

Returns -1 if str is not found.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

See also indexOf(), contains(), and count().

[since 6.2] qsizetype QString::lastIndexOf(const QRegularExpression &re, QRegularExpressionMatch *rmatch = nullptr) const

This function overloads lastIndexOf().

Returns the index position of the last match of the regular expression re in the string. Returns -1 if re didn't match anywhere.

If the match is successful and rmatch is not nullptr, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch.

Example:

QString str = "the minimum";
str.lastIndexOf(QRegularExpression("m[aeiou]"));      // returns 8

QString str = "the minimum";
QRegularExpressionMatch match;
str.lastIndexOf(QRegularExpression("m[aeiou]"), -1, &match);      // returns 8
// match.captured() == mu

This function was introduced in Qt 6.2.

qsizetype QString::lastIndexOf(const QRegularExpression &re, qsizetype from, QRegularExpressionMatch *rmatch = nullptr) const

Returns the index position of the last match of the regular expression re in the string, which starts before the index position from.

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

Returns -1 if re didn't match anywhere.

If the match is successful and rmatch is not nullptr, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch.

Example:

QString str = "the minimum";
str.lastIndexOf(QRegularExpression("m[aeiou]"));      // returns 8

QString str = "the minimum";
QRegularExpressionMatch match;
str.lastIndexOf(QRegularExpression("m[aeiou]"), -1, &match);      // returns 8
// match.captured() == mu

QString QString::left(qsizetype n) const

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

If you know that n cannot be out of bounds, use first() instead in new code, because it is faster.

The entire string is returned if n is greater than or equal to size(), or less than zero.

See also first(), last(), startsWith(), chopped(), chop(), and truncate().

QString QString::leftJustified(qsizetype width, QChar fill = u' ', bool truncate = false) const

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

If truncate is false and the size() of the string is more than width, then the returned string is a copy of the string.

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

If truncate is true and the size() of the string is more than width, then any characters in a copy of the string after position width are removed, and the copy is returned.

QString str = "Pineapple";
str = str.leftJustified(5, '.', true);    // str == "Pinea"

See also rightJustified().

qsizetype QString::length() const

Returns the number of characters in this string. Equivalent to size().

See also resize().

[static] int QString::localeAwareCompare(const QString &s1, const QString &s2)

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 compare(), QLocale, and Comparing Strings.

int QString::localeAwareCompare(const QString &other) const

This function overloads localeAwareCompare().

Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

Same as localeAwareCompare(*this, other).

See also Comparing Strings.

[since 6.0] int QString::localeAwareCompare(QStringView other) const

This function overloads localeAwareCompare().

Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

Same as localeAwareCompare(*this, other).

This function was introduced in Qt 6.0.

See also Comparing Strings.

[static, since 6.0] int QString::localeAwareCompare(QStringView s1, QStringView s2)

This function overloads localeAwareCompare().

Compares s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2.

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

This function was introduced in Qt 6.0.

See also Comparing Strings.

QString QString::mid(qsizetype position, qsizetype n = -1) const

Returns a string that contains n characters of this string, starting at the specified position index.

If you know that position and n cannot be out of bounds, use sliced() instead in new code, because it is faster.

Returns a null string if the position index exceeds the length of the string. If there are less than n characters available in the string starting at the given position, or if n is -1 (default), the function returns all characters that are available from the specified position.

See also first(), last(), sliced(), chopped(), chop(), and truncate().

QString QString::normalized(QString::NormalizationForm mode, QChar::UnicodeVersion version = QChar::Unicode_Unassigned) const

Returns the string in the given Unicode normalization mode, according to the given version of the Unicode standard.

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

Returns a string equivalent of the number n according to the specified base.

The base is 10 by default and must be between 2 and 36. For bases other than 10, n is treated as an unsigned integer.

The formatting always uses QLocale::C, i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString() with the appropriate locale.

long a = 63;
QString s = QString::number(a, 16);             // s == "3f"
QString t = QString::number(a, 16).toUpper();     // t == "3F"

See also setNum().

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

[static] QString QString::number(double n, char format = 'g', int precision = 6)

Returns a string representing the floating-point number n.

Returns a string that represents n, formatted according to the specified format and precision.

For formats with an exponent, the exponent will show its sign and have at least two digits, left-padding the exponent with zero if needed.

See also setNum(), QLocale::toString(), QLocale::FloatingPointPrecisionOption, and Number Formats.

QString &QString::prepend(const QString &str)

Prepends the string str to the beginning of this string and returns a reference to this string.

This operation is typically very fast (constant time), because QString preallocates extra space at the beginning of the string data, so it can grow without reallocating the entire string each time.

Example:

QString x = "ship";
QString y = "air";
x.prepend(y);
// x == "airship"

See also append() and insert().

QString &QString::prepend(QChar ch)

This function overloads prepend().

Prepends the character ch to this string.

QString &QString::prepend(const QChar *str, qsizetype len)

This function overloads prepend().

Prepends len characters from the QChar array str to this string and returns a reference to this string.

[since 6.0] QString &QString::prepend(QStringView str)

This function overloads prepend().

Prepends the string view str to the beginning of this string and returns a reference to this string.

This function was introduced in Qt 6.0.

QString &QString::prepend(QLatin1StringView str)

This function overloads prepend().

Prepends the Latin-1 string viewed by str to this string.

[since 6.5] QString &QString::prepend(QUtf8StringView str)

This function overloads prepend().

Prepends the UTF-8 string view str to this string.

This function was introduced in Qt 6.5.

QString &QString::prepend(const char *str)

This function overloads prepend().

Prepends the string str to this string. The const char pointer is converted to Unicode using the fromUtf8() function.

You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

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

This function overloads prepend().

Prepends the byte array ba to this string. The byte array is converted to Unicode using the fromUtf8() function.

You can disable this function by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr(), for example.

void QString::push_back(const QString &other)

This function is provided for STL compatibility, appending the given other string onto the end of this string. It is equivalent to append(other).

See also append().

void QString::push_back(QChar ch)

This is an overloaded function.

Appends the given ch character onto the end of this string.

void QString::push_front(const QString &other)

This function is provided for STL compatibility, prepending the given other string to the beginning of this string. It is equivalent to prepend(other).

See also prepend().

void QString::push_front(QChar ch)

This is an overloaded function.

Prepends the given ch character to the beginning of this string.

QString::reverse_iterator QString::rbegin()

Returns a STL-style reverse iterator pointing to the first character in the string, in reverse order.

See also begin(), crbegin(), and rend().

QString::const_reverse_iterator QString::rbegin() const

This is an overloaded function.

QString &QString::remove(qsizetype position, qsizetype n)

Removes n characters from the string, starting at the given position index, and returns a reference to the string.

If the specified position index is within the string, but position + n is beyond the end of the string, the string is truncated at the specified position.

If n is <= 0 nothing is changed.

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

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze() after the last change to the string's size.

See also insert() and replace().

QString &QString::remove(QChar ch, Qt::CaseSensitivity cs = Qt::CaseSensitive)

Removes every occurrence of the character ch in this string, and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString t = "Ali Baba";
t.remove(QChar('a'), Qt::CaseInsensitive);
// t == "li Bb"

This is the same as replace(ch, "", cs).

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze() after the last change to the string's size.

See also replace().

QString &QString::remove(QLatin1StringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This is an overloaded function.

Removes every occurrence of the given Latin-1 string viewed by str from this string, and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

This is the same as replace(str, "", cs).

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze() after the last change to the string's size.

See also replace().

QString &QString::remove(const QString &str, Qt::CaseSensitivity cs = Qt::CaseSensitive)

Removes every occurrence of the given str string in this string, and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

This is the same as replace(str, "", cs).

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze() after the last change to the string's size.

See also replace().

QString &QString::remove(const QRegularExpression &re)

Removes every occurrence of the regular expression re in the string, and returns a reference to the string. For example:

QString r = "Telephone";
r.remove(QRegularExpression("[aeiou]."));
// r == "The"

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze() after the last change to the string's size.

See also indexOf(), lastIndexOf(), and replace().

[since 6.5] QString &QString::removeAt(qsizetype pos)

Removes the character at index pos. If pos is out of bounds (i.e. pos >= size()), this function does nothing.

This function was introduced in Qt 6.5.

See also remove().

[since 6.5] QString &QString::removeFirst()

Removes the first character in this string. If the string is empty, this function does nothing.

This function was introduced in Qt 6.5.

See also remove().

[since 6.1] template <typename Predicate> QString &QString::removeIf(Predicate pred)

Removes all elements for which the predicate pred returns true from the string. Returns a reference to the string.

This function was introduced in Qt 6.1.

See also remove().

[since 6.5] QString &QString::removeLast()

Removes the last character in this string. If the string is empty, this function does nothing.

This function was introduced in Qt 6.5.

See also remove().

QString::reverse_iterator QString::rend()

Returns a STL-style reverse iterator pointing just after the last character in the string, in reverse order.

See also end(), crend(), and rbegin().

QString::const_reverse_iterator QString::rend() const

This is an overloaded function.

QString QString::repeated(qsizetype times) const

Returns a copy of this string repeated the specified number of times.

If times is less than 1, an empty string is returned.

Example:

QString str("ab");
str.repeated(4);            // returns "abababab"

QString &QString::replace(qsizetype position, qsizetype n, const QString &after)

Replaces n characters beginning at index position with the string after and returns a reference to this string.

Example:

QString x = "Say yes!";
QString y = "no";
x.replace(4, 3, y);
// x == "Say no!"

See also insert() and remove().

QString &QString::replace(qsizetype position, qsizetype n, QChar after)

This function overloads replace().

Replaces n characters beginning at index position with the character after and returns a reference to this string.

QString &QString::replace(qsizetype position, qsizetype n, const QChar *unicode, qsizetype size)

This function overloads replace().

Replaces n characters beginning at index position with the first size characters of the QChar array unicode and returns a reference to this string.

QString &QString::replace(QChar before, QChar after, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces every occurrence of the character before with the character after and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

QString &QString::replace(const QChar *before, qsizetype blen, const QChar *after, qsizetype alen, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces each occurrence in this string of the first blen characters of before with the first alen characters of after and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

QString &QString::replace(QLatin1StringView before, QLatin1StringView after, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces every occurrence in this string of the Latin-1 string viewed by before with the Latin-1 string viewed by after, and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

QString &QString::replace(QLatin1StringView before, const QString &after, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces every occurrence in this string of the Latin-1 string viewed by before with the string after, and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

QString &QString::replace(const QString &before, QLatin1StringView after, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces every occurrence of the string before with the string after and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

QString &QString::replace(const QString &before, const QString &after, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces every occurrence of the string before with the string after and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

Example:

QString str = "colour behaviour flavour neighbour";
str.replace(QString("ou"), QString("o"));
// str == "color behavior flavor neighbor"

Example:

QString equis = "xxxxxx";
equis.replace("xx", "x");
// equis == "xxx"

QString &QString::replace(QChar ch, const QString &after, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces every occurrence of the character ch in the string with after and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

QString &QString::replace(QChar c, QLatin1StringView after, Qt::CaseSensitivity cs = Qt::CaseSensitive)

This function overloads replace().

Replaces every occurrence of the character c with the string after and returns a reference to this string.

If cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.

QString &QString::replace(const QRegularExpression &re, const QString &after)

This function overloads replace().

Replaces every occurrence of the regular expression re in the string with after. Returns a reference to the string. For example:

QString s = "Banana";
s.replace(QRegularExpression("a[mn]"), "ox");
// s == "Boxoxa"

For regular expressions containing capturing groups, occurrences of \1, \2, ..., in after are replaced with the string captured by the corresponding capturing group.

QString t = "A <i>bon mot</i>.";
t.replace(QRegularExpression("<i>([^<]*)</i>"), "\\emph{\\1}");
// t == "A \\emph{bon mot}."

See also indexOf(), lastIndexOf(), remove(), QRegularExpression, and QRegularExpressionMatch.

void QString::reserve(qsizetype size)

Ensures the string has space for at least size characters.

If you know in advance how large the string will be, you can call this function to save repeated reallocation in the course of building it. This can improve performance when building a string incrementally. A long sequence of operations that add to a string may trigger several reallocations, the last of which may leave you with significantly more space than you really need, which is less efficient than doing a single allocation of the right size at the start.

If in doubt about how much space shall be needed, it is usually better to use an upper bound as size, or a high estimate of the most likely size, if a strict upper bound would be much bigger than this. If size is an underestimate, the string will grow as needed once the reserved size is exceeded, which may lead to a larger allocation than your best overestimate would have and will slow the operation that triggers it.

This function is useful for code that needs to build up a long string and wants to avoid repeated reallocation. In this example, we want to add to the string until some condition is true, and we're fairly sure that size is large enough to make a call to reserve() worthwhile:

QString result;
qsizetype maxSize;
bool condition;
QChar nextChar;

result.reserve(maxSize);

while (condition)
    result.append(nextChar);

result.squeeze();

See also squeeze(), capacity(), and resize().

void QString::resize(qsizetype size)

Sets the size of the string to size characters.

If size is greater than the current size, the string is extended to make it size characters long with the extra characters added to the end. The new characters are uninitialized.

If size is less than the current size, characters beyond position size are excluded from the string.

Example:

QString s = "Hello world";
s.resize(5);
// s == "Hello"

s.resize(8);
// s == "Hello???" (where ? stands for any character)

If you want to append a certain number of identical characters to the string, use the resize(qsizetype, QChar) overload.

If you want to expand the string so that it reaches a certain width and fill the new positions with a particular character, use the leftJustified() function:

If size is negative, it is equivalent to passing zero.

QString r = "Hello";
r = r.leftJustified(10, ' ');
// r == "Hello     "

See also truncate(), reserve(), and squeeze().

void QString::resize(qsizetype newSize, QChar fillChar)

This is an overloaded function.

Unlike resize(qsizetype), this overload initializes the new characters to fillChar:

QString t = "Hello";
r.resize(t.size() + 10, 'X');
// t == "HelloXXXXXXXXXX"

QString QString::right(qsizetype n) const

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

If you know that n cannot be out of bounds, use last() instead in new code, because it is faster.

The entire string is returned if n is greater than or equal to size(), or less than zero.

See also endsWith(), last(), first(), sliced(), chopped(), chop(), and truncate().

QString QString::rightJustified(qsizetype width, QChar fill = u' ', bool truncate = false) const

Returns a string of size() width that contains the fill character followed by the string. For example:

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

If truncate is false and the size() of the string is more than width, then the returned string is a copy of the string.

If truncate is true and the size() of the string is more than width, then the resulting string is truncated at position width.

QString str = "Pineapple";
str = str.rightJustified(5, '.', true);    // str == "Pinea"

See also leftJustified().

QString QString::section(QChar sep, qsizetype start, qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const

This function returns a section of the string.

This string is treated as a sequence of fields separated by the character, sep. The returned string consists of the fields from position start to position end inclusive. If end is not specified, all fields from position start to the end of the string are included. Fields are numbered 0, 1, 2, etc., counting from the left, and -1, -2, etc., counting from right to left.

The flags argument can be used to affect some aspects of the function's behavior, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags.

QString str;
QString csv = "forename,middlename,surname,phone";
QString path = "/usr/local/bin/myapp"; // First field is empty
QString::SectionFlag flag = QString::SectionSkipEmpty;

str = csv.section(',', 2, 2);   // str == "surname"
str = path.section('/', 3, 4);  // str == "bin/myapp"
str = path.section('/', 3, 3, flag); // str == "myapp"

If start or end is negative, we count fields from the right of the string, the right-most field being -1, the one from right-most field being -2, and so on.

str = csv.section(',', -3, -2);  // str == "middlename,surname"
str = path.section('/', -1); // str == "myapp"

See also split().

QString QString::section(const QString &sep, qsizetype start, qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const

This function overloads section().

QString str;
QString data = "forename**middlename**surname**phone";

str = data.section("**", 2, 2); // str == "surname"
str = data.section("**", -3, -2); // str == "middlename**surname"

See also split().

QString QString::section(const QRegularExpression &re, qsizetype start, qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const

This function overloads section().

This string is treated as a sequence of fields separated by the regular expression, re.

QString line = "forename\tmiddlename  surname \t \t phone";
QRegularExpression sep("\\s+");
str = line.section(sep, 2, 2); // str == "surname"
str = line.section(sep, -3, -2); // str == "middlename  surname"

See also split() and simplified().

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

Sets the string to the printed value of n in the specified base, and returns a reference to the string.

The base is 10 by default and must be between 2 and 36.

QString str;
str.setNum(1234);       // str == "1234"

The formatting always uses QLocale::C, i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString() with the appropriate locale.

See also number().

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

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

This is an overloaded function.

QString &QString::setNum(float n, char format = 'g', int precision = 6)

This is an overloaded function.

Sets the string to the printed value of n, formatted according to the given format and precision, and returns a reference to the string.

The formatting always uses QLocale::C, i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString() with the appropriate locale.

See also number().

QString &QString::setNum(double n, char format = 'g', int precision = 6)

This is an overloaded function.

Sets the string to the printed value of n, formatted according to the given format and precision, and returns a reference to the string.

See also number(), QLocale::FloatingPointPrecisionOption, and Number Formats.

QString &QString::setRawData(const QChar *unicode, qsizetype size)

Resets the QString to use the first size Unicode characters in the array unicode. The data in unicode is not copied. The caller must be able to guarantee that unicode will not be deleted or modified as long as the QString (or an unmodified copy of it) exists.

This function can be used instead of fromRawData() to re-use existings QString objects to save memory re-allocations.

See also fromRawData().

QString &QString::setUnicode(const QChar *unicode, qsizetype size)

Resizes the string to size characters and copies unicode into the string.

If unicode is nullptr, nothing is copied, but the string is still resized to size.

See also unicode() and setUtf16().

QString &QString::setUtf16(const ushort *unicode, qsizetype size)

Resizes the string to size characters and copies unicode into the string.

If unicode is nullptr, nothing is copied, but the string is still resized to size.

Note that unlike fromUtf16(), this function does not consider BOMs and possibly differing byte ordering.

See also utf16() and setUnicode().

void QString::shrink_to_fit()

This function is provided for STL compatibility. It is equivalent to squeeze().