path: root/src/corelib/text/qanystringview.qdoc

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/*!
    \class QAnyStringView
    \inmodule QtCore
    \since 6.0
    \brief 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

    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 to keep old source working
    efficiently. It is expected that by Qt 7, the Latin-1 support will
    be removed.

    The string may be represented as an array (or an array-compatible
    data-structure such as QString, std::basic_string, etc.) of \c
    char, \c char8_t, QChar, \c ushort, \c char16_t or (on platforms,
    such as Windows, where it is a 16-bit type) \c 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, \c{(const QChar*, int)},
    QUtf8StringView, QLatin1String (but see above), and QChar), while
    at the same time enabling even more string data sources to be
    passed to the function, such as \c{u8"Hello World"}, a \c char8_t
    string literal.

    Like elsewhere in Qt, QAnyStringView assumes \c char data is encoded
    in UTF-8, unless it is presented as a QLatin1String.

    QAnyStringViews should be passed by value, not by reference-to-const:
    \snippet code/src_corelib_text_qanystringview.cpp 0

    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 \e{Literal Type}.

    \section2 Compatible Character Types

    QAnyStringView accepts strings over a variety of character types:

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

    The 8-bit character types are interpreted as UTF-8 data (except when
    presented as a QLatin1String) while the 16-bit character types are
    interpreted as UTF-16 data in host byte order (the same as QString).

    \section2 Sizes and Sub-Strings

    All sizes and positions in QAnyStringView functions are in the
    encoding's code points (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).

    \sa QUtf8StringView, QStringView
*/

/*!
    \typedef QAnyStringView::difference_type

    Alias for \c{std::ptrdiff_t}. Provided for compatibility with the STL.
*/

/*!
    \typedef QAnyStringView::size_type

    Alias for qsizetype. Provided for compatibility with the STL.
*/

/*!
    \fn QAnyStringView::QAnyStringView()

    Constructs a null string view.

    \sa isNull()
*/

/*!
    \fn QAnyStringView::QAnyStringView(std::nullptr_t)

    Constructs a null string view.

    \sa isNull()
*/

/*!
    \fn template <typename Char> QAnyStringView::QAnyStringView(const Char *str, qsizetype len)

    Constructs a string view on \a str with length \a len.

    The range \c{[str,len)} must remain valid for the lifetime of this string view object.

    Passing \nullptr as \a str is safe if \a len is 0, too, and results in a null string view.

    The behavior is undefined if \a len is negative or, when positive, if \a str is \nullptr.

    This constructor only participates in overload resolution if \c Char is a compatible
    character type.

    \sa isNull(), {Compatible Character Types}
*/

/*!
    \fn template <typename Char> QAnyStringView::QAnyStringView(const Char *first, const Char *last)

    Constructs a string view on \a first with length (\a last - \a first).

    The range \c{[first,last)} must remain valid for the lifetime of
    this string view object.

    Passing \c \nullptr as \a first is safe if \a last is \nullptr, too,
    and results in a null string view.

    The behavior is undefined if \a last precedes \a first, or \a first
    is \nullptr and \a last is not.

    This constructor only participates in overload resolution if \c Char
    is a compatible character type.

    \sa isNull(), {Compatible Character Types}
*/

/*!
    \fn template <typename Char> QAnyStringView::QAnyStringView(const Char *str)

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

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

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

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

    \sa isNull(), {Compatible Character Types}
*/

/*!
    \fn template <typename Char, size_t N> QAnyStringView::QAnyStringView(const Char (&string)[N])

    Constructs a string view on the character string literal \a string.
    The view covers the array until the first \c{Char(0)} is encountered,
    or \c N, whichever comes first.
    If you need the full array, use fromArray() instead.

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

    This constructor only participates in overload resolution if \a
    string is an actual array and \c Char is a compatible character
    type.

    \sa {Compatible Character Types}
*/

/*!
    \fn QAnyStringView::QAnyStringView(const QString &str)

    Constructs a string view on \a str.

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

    The string view will be null if and only if \c{str.isNull()}.
*/

/*!
    \fn QAnyStringView::QAnyStringView(const QByteArray &str)

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

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

    The string view will be null if and only if \c{str.isNull()}.
*/

/*!
    \fn template <typename Char, size_t Size> static QAnyStringView fromArray(const Char (&string)[Size]) noexcept

    Constructs a string view on the full character string literal \a string,
    including any trailing \c{Char(0)}. If you don't want the
    null-terminator included in the view then you can use the constructor
    overload taking a pointer and a size:

    \snippet code/src_corelib_text_qanystringview.cpp 2

    Alternatively you can use the constructor overload taking an
    array literal which will create a view up to, but not including,
    the first null-terminator in the data.

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

    This function will work with any array literal if \c Char is a
    compatible character type.
*/

/*!
    \fn 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.
*/

/*!
    \fn const void *QAnyStringView::data() const

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

    \note The character array represented by the return value is \e not null-terminated.

    \sa size_bytes()
*/

/*!
    \fn bool QAnyStringView::empty() const

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

    This function is provided for STL compatibility.

    \sa isEmpty(), isNull(), size()
*/

/*!
    \fn bool QAnyStringView::isEmpty() const

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

    This function is provided for compatibility with other Qt containers.

    \sa empty(), isNull(), size()
*/

/*!
    \fn bool QAnyStringView::isNull() const

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

    This functions is provided for compatibility with other Qt containers.

    \sa empty(), isEmpty(), size()
*/

/*!
    \fn qsizetype QAnyStringView::size() const

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

    \sa empty(), isEmpty(), isNull(), size_bytes(), {Sizes and Sub-Strings}
*/

/*!
    \fn 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.

    \sa size(), data()
*/

/*!
    \fn int QAnyStringView::length() const

    Same as size().

    This function is provided for compatibility with other Qt containers.

    \sa size()
*/

/*!
    \fn QChar QAnyStringView::front() const

    Returns the first character in the string.

    This function is provided for STL compatibility.

    \warning Calling this function on an empty string view constitutes
    undefined behavior.

    \sa back(), {Sizes and Sub-Strings}
*/

/*!
    \fn QChar QAnyStringView::back() const

    Returns the last character in the string.

    This function is provided for STL compatibility.

    \warning Calling this function on an empty string view constitutes
    undefined behavior.

    \sa front(), {Sizes and Sub-Strings}
*/

/*!
    \fn QAnyStringView::compare(QAnyStringView lhs, QAnyStringView rhs, Qt::CaseSensitivity cs)

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

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

    \sa operator==(), operator<(), operator>()
*/

/*!
    \fn bool QAnyStringView::operator==(QAnyStringView lhs, QAnyStringView rhs)
    \fn bool QAnyStringView::operator!=(QAnyStringView lhs, QAnyStringView rhs)
    \fn bool QAnyStringView::operator<=(QAnyStringView lhs, QAnyStringView rhs)
    \fn bool QAnyStringView::operator>=(QAnyStringView lhs, QAnyStringView rhs)
    \fn bool QAnyStringView::operator<(QAnyStringView lhs, QAnyStringView rhs)
    \fn bool QAnyStringView::operator>(QAnyStringView lhs, QAnyStringView rhs)

    Operators that compare \a lhs to \a rhs.

    \sa compare()
*/

/*!
    \fn template <typename QStringLike> qToAnyStringViewIgnoringNull(const QStringLike &s);
    \since 6.0
    \internal

    Convert \a s to a QAnyStringView ignoring \c{s.isNull()}.

    Returns a string-view that references \a{s}'s data, but is never null.

    This is a faster way to convert a QString or QByteArray to a QAnyStringView,
    if null QStrings or QByteArrays can legitimately be treated as empty ones.

    \sa QString::isNull(), QAnyStringView
*/