QAnyStringView Class

The QAnyStringView class provides a unified view on Latin-1, UTF-8, or UTF-16 strings with a read-only subset of the QString API. \reentrant \ingroup tools \ingroup string-processing. More...

Header: #include <QAnyStringView>

Public Types

Public Functions

QAnyStringView()
QAnyStringView(const Char *str)
QAnyStringView(const QByteArray &str)
QAnyStringView(const QString &str)
QAnyStringView(const Container &str)
QChar back() const
void chop(int n)
QAnyStringView chopped(int n) const
const void *data() const
bool empty() const
QAnyStringView first(int n) const
QChar front() const
bool isEmpty() const
bool isNull() const
QAnyStringView last(int n) const
QAnyStringView left(int n) const
int length() const
QAnyStringView mid(int pos, int n = -1) const
QAnyStringView right(int n) const
int size() const
int size_bytes() const
QAnyStringView sliced(int pos) const
QAnyStringView sliced(int pos, int n) const
QString toString() const
void truncate(int n)

Static Public Members

int compare(QAnyStringView lhs, QAnyStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive)
QString convertToQString(QAnyStringView string)
bool operator!=(QAnyStringView lhs, QAnyStringView rhs)
bool operator<(QAnyStringView lhs, QAnyStringView rhs)
bool operator<=(QAnyStringView lhs, QAnyStringView rhs)
bool operator==(QAnyStringView lhs, QAnyStringView rhs)
bool operator>(QAnyStringView lhs, QAnyStringView rhs)
bool operator>=(QAnyStringView lhs, QAnyStringView rhs)

Detailed Description

\inmoduleQtCore \since 6.0

A QAnyStringView references a contiguous portion of a string it does not own. It acts as an interface type to all kinds of strings, without the need to construct a QString first.

Unlike QStringView and QUtf8StringView, QAnyStringView can hold strings of any of the following encodings: UTF-8, UTF-16, and Latin-1. The latter is supported because Latin-1, unlike UTF-8, can be efficiently compared to UTF-16 data: a length mismatch already means the strings cannot be equal. This is not true for UTF-8/UTF-16 comparisons, because UTF-8 is a variable-length encoding.

The string may be represented as an array (or an array-compatible data-structure such as QString, std::basic_string, etc.) of char, char8_t, QChar, ushort, char16_t or (on platforms, such as Windows, where it is a 16-bit type) wchar_t.

QAnyStringView is designed as an interface type; its main use-case is as a function parameter type. When QAnyStringViews are used as automatic variables or data members, care must be taken to ensure that the referenced string data (for example, owned by a QString) outlives the QAnyStringView on all code paths, lest the string view ends up referencing deleted data.

When used as an interface type, QAnyStringView allows a single function to accept a wide variety of string data sources. One function accepting QAnyStringView thus replaces five function overloads (taking QString, (const QChar*, qsizetype), QUtf8StringView, QLatin1StringView (but see above), and QChar), while at the same time enabling even more string data sources to be passed to the function, such as u8"Hello World", a char8_t string literal.

Like elsewhere in Qt, QAnyStringView assumes char data is encoded in UTF-8, unless it is presented as a QLatin1StringView.

Since Qt 6.4, however, UTF-8 string literals that are pure US-ASCII are automatically stored as Latin-1. This is a compile-time check with no runtime overhead. The feature requires compiling in C++20, or with a recent GCC.

QAnyStringViews should be passed by value, not by reference-to-const:

     void myfun1(QAnyStringView sv);        // preferred
     void myfun2(const QAnyStringView &sv); // compiles and works, but slower

QAnyStringView can also be used as the return value of a function, but this is not recommended. QUtf8StringView or QStringView are better suited as function return values. If you call a function returning QAnyStringView, take extra care to not keep the QAnyStringView around longer than the function promises to keep the referenced string data alive. If in doubt, obtain a strong reference to the data by calling toString() to convert the QAnyStringView into a QString.

QAnyStringView is a Literal Type.

Compatible Character Types

QAnyStringView accepts strings over a variety of character types:

  • char (both signed and unsigned)
  • char8_t (C++20 only)
  • char16_t
  • wchar_t (where it's a 16-bit type, e.g. Windows)
  • ushort
  • QChar

The 8-bit character types are interpreted as UTF-8 data (except when presented as a QLatin1StringView) while the 16-bit character types are interpreted as UTF-16 data in host byte order (the same as QString).

Sizes and Sub-Strings

All sizes and positions in QAnyStringView functions are in the encoding's code units (that is, UTF-16 surrogate pairs count as two for the purposes of these functions, the same as in QString, and UTF-8 multibyte sequences count as two, three or four, depending on their length).

See also QUtf8StringView and QStringView.

Member Type Documentation

QAnyStringView::difference_type

Alias for std::ptrdiff_t. Provided for compatibility with the STL.

QAnyStringView::size_type

Alias for qsizetype. Provided for compatibility with the STL.

Member Function Documentation

[constexpr noexcept] QAnyStringView::QAnyStringView()

Constructs a null string view.

See also isNull().

[constexpr noexcept] template <typename Char> QAnyStringView::QAnyStringView(const Char *str)

Constructs a string view on str. The length is determined by scanning for the first Char(0).

str must remain valid for the lifetime of this string view object.

Passing nullptr as str is safe and results in a null string view.

This constructor only participates in overload resolution if str is not an array and if Char is a compatible character type.

See also isNull() and Compatible Character Types.

[noexcept] QAnyStringView::QAnyStringView(const QByteArray &str)

Constructs a string view on str. The data in str is interpreted as UTF-8.

str.data() must remain valid for the lifetime of this string view object.

The string view will be null if and only if str.isNull().

[noexcept] QAnyStringView::QAnyStringView(const QString &str)

Constructs a string view on str.

str.data() must remain valid for the lifetime of this string view object.

The string view will be null if and only if str.isNull().

[constexpr noexcept] template <typename Container, int> QAnyStringView::QAnyStringView(const Container &str)

Constructs a string view on str. The length is taken from std::size(str).

std::data(str) must remain valid for the lifetime of this string view object.

This constructor only participates in overload resolution if Container is a container with a compatible character type as value_type.

The string view will be empty if and only if std::size(str) == 0. It is unspecified whether this constructor can result in a null string view (std::data(str) would have to return nullptr for this).

See also isNull() and isEmpty().

[constexpr] QChar QAnyStringView::back() const

Returns the last character in the string view.

This function is provided for STL compatibility.

Warning: Calling this function on an empty string view constitutes undefined behavior.

See also front() and Sizes and Sub-Strings.

[constexpr] void QAnyStringView::chop(int n)

\since6.5

Truncates this string view by n code points.

Same as *this = first(size() - n).

Note: The behavior is undefined when n < 0 or n > size().

See also sliced(), first(), last(), chopped(), truncate(), and Sizes and Sub-Strings.

[constexpr] QAnyStringView QAnyStringView::chopped(int n) const

\since6.5

Returns the substring of length size() - n starting at the beginning of this object.

Same as first(size() - n).

Note: The behavior is undefined when n < 0 or n > size().

See also sliced(), first(), last(), chop(), truncate(), and Sizes and Sub-Strings.

[static noexcept] int QAnyStringView::compare(QAnyStringView lhs, QAnyStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive)

Returns an integer that compares to zero as lhs compares to rhs.

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

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

[constexpr noexcept] const void *QAnyStringView::data() const

Returns a const pointer to the first character in the string view.

Note: The character array represented by the return value is not null-terminated.

See also size_bytes().

[constexpr noexcept] bool QAnyStringView::empty() const

Returns whether this string view is empty - that is, whether size() == 0.

This function is provided for STL compatibility.

See also isEmpty(), isNull(), and size().

[constexpr] QAnyStringView QAnyStringView::first(int n) const

\since6.5

Returns a string view that contains the first n code points of this string view.

Note: The behavior is undefined when n < 0 or n > size().

See also last(), sliced(), chopped(), chop(), truncate(), and Sizes and Sub-Strings.

[constexpr] QChar QAnyStringView::front() const

Returns the first character in the string view.

This function is provided for STL compatibility.

Warning: Calling this function on an empty string view constitutes undefined behavior.

See also back() and Sizes and Sub-Strings.

[constexpr noexcept] bool QAnyStringView::isEmpty() const

Returns whether this string view is empty - that is, whether size() == 0.

This function is provided for compatibility with other Qt containers.

See also empty(), isNull(), and size().

[constexpr noexcept] bool QAnyStringView::isNull() const

Returns whether this string view is null - that is, whether data() == nullptr.

This functions is provided for compatibility with other Qt containers.

See also empty(), isEmpty(), and size().

[constexpr] QAnyStringView QAnyStringView::last(int n) const

\since6.5

Returns a string view that contains the last n code points of this string view.

Note: The behavior is undefined when n < 0 or n > size().

See also first(), sliced(), chopped(), chop(), truncate(), and Sizes and Sub-Strings.

[constexpr] QAnyStringView QAnyStringView::left(int n) const

\since6.5

\deprecatedUse first() instead in new code.

Returns the substring of length n starting at position 0 in this object.

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

See also first(), last(), sliced(), chopped(), chop(), truncate(), and Sizes and Sub-Strings.

[constexpr noexcept] int QAnyStringView::length() const

Same as size().

This function is provided for compatibility with other Qt containers.

See also size().

[constexpr] QAnyStringView QAnyStringView::mid(int pos, int n = -1) const

\since6.5

Returns the substring of length n starting at position pos in this object.

\deprecatedUse sliced() instead in new code.

Returns an empty string view if n exceeds the length of the string view. If there are less than n code points available in the string view starting at pos, or if n is negative (default), the function returns all code points that are available from pos.

See also first(), last(), sliced(), chopped(), chop(), truncate(), and Sizes and Sub-Strings.

\since6.5

\deprecatedUse last() instead in new code.

Returns the substring of length n starting at position size() - n in this object.

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

See also first(), last(), sliced(), chopped(), chop(), truncate(), and Sizes and Sub-Strings.

[constexpr noexcept] int QAnyStringView::size() const

Returns the size of this string view, in the encoding's code points.

See also empty(), isEmpty(), isNull(), size_bytes(), and Sizes and Sub-Strings.

[constexpr noexcept] int QAnyStringView::size_bytes() const

Returns the size of this string view, but in bytes, not code-points.

You can use this function together with data() for hashing or serialization.

This function is provided for STL compatibility.

See also size() and data().

[constexpr] QAnyStringView QAnyStringView::sliced(int pos) const

\since6.5

Returns a string view starting at position pos in this object, and extending to its end.

Note: The behavior is undefined when pos < 0 or pos > size().

See also first(), last(), chopped(), chop(), truncate(), and Sizes and Sub-Strings.

[constexpr] QAnyStringView QAnyStringView::sliced(int pos, int n) const

\since6.5

Returns a string view containing n code points of this string view, starting at position pos.

Note: The behavior is undefined when pos < 0, n < 0, or pos + n > size().

See also first(), last(), chopped(), chop(), truncate(), and Sizes and Sub-Strings.

QString QAnyStringView::toString() const

Returns a deep copy of this string view's data as a QString.

The return value will be a null QString if and only if this string view is null.

[constexpr] void QAnyStringView::truncate(int n)

\since6.5

Truncates this string view to n code points.

Same as *this = first(n).

Note: The behavior is undefined when n < 0 or n > size().

See also sliced(), first(), last(), chopped(), chop(), and Sizes and Sub-Strings.

Related Non-Members

[noexcept] bool operator!=(QAnyStringView lhs, QAnyStringView rhs)

[noexcept] bool operator<(QAnyStringView lhs, QAnyStringView rhs)

[noexcept] bool operator<=(QAnyStringView lhs, QAnyStringView rhs)

[noexcept] bool operator==(QAnyStringView lhs, QAnyStringView rhs)

[noexcept] bool operator>(QAnyStringView lhs, QAnyStringView rhs)

[noexcept] bool operator>=(QAnyStringView lhs, QAnyStringView rhs)

Operators that compare lhs to rhs.

See also compare().

QString convertToQString(QAnyStringView string)

\since6.0 \internal

Returns a UTF-16 representation of string as a QString.

See also QString::toLatin1(), QStringView::toLatin1(), QtPrivate::convertToUtf8(), QtPrivate::convertToLocal8Bit(), and QtPrivate::convertToUcs4().