/**************************************************************************** ** ** Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz ** Contact: https://www.qt.io/licensing/ ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:FDL$ ** Commercial License Usage ** Licensees holding valid commercial Qt licenses may use this file in ** accordance with the commercial license agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and The Qt Company. For licensing terms ** and conditions see https://www.qt.io/terms-conditions. For further ** information use the contact form at https://www.qt.io/contact-us. ** ** GNU Free Documentation License Usage ** Alternatively, this file may be used under the terms of the GNU Free ** Documentation License version 1.3 as published by the Free Software ** Foundation and appearing in the file included in the packaging of ** this file. Please review the following information to ensure ** the GNU Free Documentation License version 1.3 requirements ** will be met: https://www.gnu.org/licenses/fdl-1.3.html. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \class QUtf8StringView \inmodule QtCore \since 6.0 \brief The QUtf8StringView class provides a unified view on UTF-8 strings with a read-only subset of the QString API. \reentrant \ingroup tools \ingroup string-processing A QUtf8StringView references a contiguous portion of a UTF-8 string it does not own. It acts as an interface type to all kinds of UTF-8 string, without the need to construct a QString or QByteArray first. The UTF-8 string may be represented as an array (or an array-compatible data-structure such as std::basic_string, etc.) of \c char8_t, \c char, \c{signed char} or \c{unsigned char}. QUtf8StringView is designed as an interface type; its main use-case is as a function parameter type. When QUtf8StringViews are used as automatic variables or data members, care must be taken to ensure that the referenced string data (for example, owned by a std::u8string) outlives the QUtf8StringView on all code paths, lest the string view ends up referencing deleted data. When used as an interface type, QUtf8StringView allows a single function to accept a wide variety of UTF-8 string data sources. One function accepting QUtf8StringView thus replaces several function overloads (taking e.g. QByteArray), 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 (C++20) or \c char (C++17) string literal. The \c char8_t incompatibility between C++17 and C++20 goes away when using QUtf8StringView. Like all views, QUtf8StringViews should be passed by value, not by reference-to-const: \snippet code/src_corelib_text_qutf8stringview.cpp 0 If you want to give your users maximum freedom in what strings they can pass to your function, consider using QAnyStringView instead. QUtf8StringView can also be used as the return value of a function. If you call a function returning QUtf8StringView, take extra care to not keep the QUtf8StringView 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 QUtf8StringView into a QString. QUtf8StringView is a \e{Literal Type}. \section Compatible Character Types QUtf8StringView accepts strings over a variety of character types: \list \li \c char (both signed and unsigned) \li \c char8_t (C++20 only) \endlist \section Sizes and Sub-Strings All sizes and postions in QUtf8StringView functions are in UTF-8 code points (that is, UTF-8 multibyte sequences count as two, three or four, depending on their length). QUtf8StringView does not an attempt to detect or prevent slicing right through UTF-8 multibyte sequences. This is similar to the situation with QStringView and surrogate pairs. \section C++20, char8_t, and QUtf8StringView In C++20, \c{u8""} string literals changed their type from \c{const char[]} to \c{const char8_t[]}. If Qt 6 could have depended on C++20, QUtf8StringView would store \c char8_t natively, and the following functions and aliases would use (pointers to) \c char8_t: \list \li storage_type, value_type, etc \li begin(), end(), data(), etc \li front(), back(), at(), operator[]() \endlist This is what QUtf8StringView is expected to look like in Qt 7, but for Qt 6, this was not possible. Instead of locking users into a C++17-era interface for the next decade, Qt provides two QUtf8StringView classes, in different (inline) namespaces. The first, in namespace \c{q_no_char8_t}, has a value_type of \c{const char} and is universally available. The second, in namespace \c{q_has_char8_t}, has a value_type of \c{const char8_t} and is only available when compiling in C++20 mode. In C++17 mode, \c{q_no_char8_t} is an inline namespace, in C++20 it's \c{q_has_char8_t}. This means that the name "QUtf8StringView" (without explicit namespace) will denote different types in C++17 and C++20 modes. Internally, both are instantiations of the same template class, QBasicUtf8StringView. Please do not use the template class's name in your source code. All Qt APIs use \c{q_no_char8_t::QUtf8StringView} due to binary compatibility, but these APIs accept \c{q_has_char8_t::QUtf8StringView} as well, since the latter implicitly converts into the former, and vice versa. In your own code, please use only \c QUtf8StringView and/or \c{q_no_char8_t::QUtf8StringView}: \list \li If you only target C++20, then use "QUtf8StringView". It will be an alias for \c{q_has_char8_t::QUtf8StringView} and you'll never look back. \li If you only target C++17, then use "QUtf8StringView". It will be an alias for \c{q_no_char8_t::QUtf8StringView} and for the time being, you're ok. \li If you target both C++17 and C++20, then you have a choice to make: \list \li If you don't mind the source-incompatibility of return values of QUtf8StringView::data() etc changing when compiling under C++17 or C++20, use "QUtf8StringView". You will need to write your code in such a way that it adapts to the differences in the QUtf8StringView API in different C++ versions. \li If you don't want to deal with the above source-incompatibilities, or if you need to maintain binary compatibility between C++20 and C++17 builds, use "q_no_char8_t::QUtf8StringView" explicitly. Be aware that the \c{q_no_char8_t} version will disappear in Qt 7. \endlist \endlist Taken together: Just use QUtf8StringView unless you know what you're doing. \sa QAnyStringView, QUtf8StringView, QString */ /*! \typedef QUtf8StringView::storage_type Alias for \c{char}. */ /*! \typedef QUtf8StringView::value_type Alias for \c{const char}. Provided for compatibility with the STL. */ /*! \typedef QUtf8StringView::difference_type Alias for \c{std::ptrdiff_t}. Provided for compatibility with the STL. */ /*! \typedef QUtf8StringView::size_type Alias for qsizetype. Provided for compatibility with the STL. */ /*! \typedef QUtf8StringView::reference Alias for \c{value_type &}. Provided for compatibility with the STL. QUtf8StringView does not support mutable references, so this is the same as const_reference. */ /*! \typedef QUtf8StringView::const_reference Alias for \c{value_type &}. Provided for compatibility with the STL. */ /*! \typedef QUtf8StringView::pointer Alias for \c{value_type *}. Provided for compatibility with the STL. QUtf8StringView does not support mutable pointers, so this is the same as const_pointer. */ /*! \typedef QUtf8StringView::const_pointer Alias for \c{value_type *}. Provided for compatibility with the STL. */ /*! \typedef QUtf8StringView::iterator This typedef provides an STL-style const iterator for QUtf8StringView. QUtf8StringView does not support mutable iterators, so this is the same as const_iterator. \sa const_iterator, reverse_iterator */ /*! \typedef QUtf8StringView::const_iterator This typedef provides an STL-style const iterator for QUtf8StringView. \sa iterator, const_reverse_iterator */ /*! \typedef QUtf8StringView::reverse_iterator This typedef provides an STL-style const reverse iterator for QUtf8StringView. QUtf8StringView does not support mutable reverse iterators, so this is the same as const_reverse_iterator. \sa const_reverse_iterator, iterator */ /*! \typedef QUtf8StringView::const_reverse_iterator This typedef provides an STL-style const reverse iterator for QUtf8StringView. \sa reverse_iterator, const_iterator */ /*! \fn QUtf8StringView::QUtf8StringView() Constructs a null string view. \sa isNull() */ /*! \fn QUtf8StringView::QUtf8StringView(std::nullptr_t) Constructs a null string view. \sa isNull() */ /*! \fn template QUtf8StringView::QUtf8StringView(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. The compatible character types are: \c char8_t, \c char, \c{signed char} and \c{unsigned char}. */ /*! \fn template QUtf8StringView::QUtf8StringView(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. The compatible character types are: \c char8_t, \c char, \c{signed char} and \c{unsigned char}. */ /*! \fn template QUtf8StringView::QUtf8StringView(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. The compatible character types are: \c char8_t, \c char, \c{signed char} and \c{unsigned char}. */ /*! \fn template QUtf8StringView::QUtf8StringView(const Char (&string)[N]) Constructs a string view on the character string literal \a string. The length is set to \c{N-1}, excluding the trailing \c{Char(0)}. If you need the full array, use the constructor from pointer and size instead: \snippet code/src_corelib_text_qutf8stringview.cpp 2 \a string must remain valid for the lifetime of this string view object. This constructor only participates in overload resolution if \a str is an actual array and if \c Char is a compatible character type. The compatible character types are: \c char8_t, \c char, \c{signed char} and \c{unsigned char}. */ /*! \fn template QUtf8StringView::QUtf8StringView(const StdBasicString &str) Constructs a string view on \a str. The length is taken from \c{str.size()}. \c{str.data()} must remain valid for the lifetime of this string view object. This constructor only participates in overload resolution if \c StdBasicString is an instantiation of \c std::basic_string with a compatible character type. The compatible character types are: \c char8_t, \c char, \c{signed char} and \c{unsigned char}. The string view will be empty if and only if \c{str.empty()}. It is unspecified whether this constructor can result in a null string view (\c{str.data()} would have to return \nullptr for this). \sa isNull(), isEmpty() */ /*! \fn QString QUtf8StringView::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 QUtf8StringView::data() const Returns a const pointer to the first code point in the string. \note The character array represented by the return value is \e not null-terminated. \sa begin(), end(), utf8() */ /*! \fn QUtf8StringView::utf8() const Returns a const pointer to the first code point in the string. The result is returned as a \c{const char8_t*}, so this function is only available when compiling in C++20 mode. \note The character array represented by the return value is \e not null-terminated. \sa begin(), end(), data() */ /*! \fn QUtf8StringView::const_iterator QUtf8StringView::begin() const Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first code point in the string. This function is provided for STL compatibility. \sa end(), cbegin(), rbegin(), data() */ /*! \fn QUtf8StringView::const_iterator QUtf8StringView::cbegin() const Same as begin(). This function is provided for STL compatibility. \sa cend(), begin(), crbegin(), data() */ /*! \fn QUtf8StringView::const_iterator QUtf8StringView::end() const Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary code point after the last code point in the list. This function is provided for STL compatibility. \sa begin(), cend(), rend() */ /*! \fn QUtf8StringView::const_iterator QUtf8StringView::cend() const Same as end(). This function is provided for STL compatibility. \sa cbegin(), end(), crend() */ /*! \fn QUtf8StringView::const_reverse_iterator QUtf8StringView::rbegin() const Returns a const \l{STL-style iterators}{STL-style} reverse iterator pointing to the first code point in the string, in reverse order. This function is provided for STL compatibility. \sa rend(), crbegin(), begin() */ /*! \fn QUtf8StringView::const_reverse_iterator QUtf8StringView::crbegin() const Same as rbegin(). This function is provided for STL compatibility. \sa crend(), rbegin(), cbegin() */ /*! \fn QUtf8StringView::const_reverse_iterator QUtf8StringView::rend() const Returns a \l{STL-style iterators}{STL-style} reverse iterator pointing to one past the last code point in the string, in reverse order. This function is provided for STL compatibility. \sa rbegin(), crend(), end() */ /*! \fn QUtf8StringView::const_reverse_iterator QUtf8StringView::crend() const Same as rend(). This function is provided for STL compatibility. \sa crbegin(), rend(), cend() */ /*! \fn bool QUtf8StringView::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(), length() */ /*! \fn bool QUtf8StringView::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(), length() */ /*! \fn bool QUtf8StringView::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(), length() */ /*! \fn qsizetype QUtf8StringView::size() const Returns the size of this string view, in UTF-8 code points (that is, multi-byte sequences count as more than one for the purposes of this function, the same as surrogate pairs in QString and QStringView). \sa empty(), isEmpty(), isNull(), length() */ /*! \fn int QUtf8StringView::length() const \obsolete Use size() and port callers to qsizetype. Same as size(), except returns the result as an \c int. This function is provided for compatibility with other Qt containers. \warning QUtf8StringView can represent strings with more than 2\sup{31} code points. Calling this function on a string view for which size() returns a value greater than \c{INT_MAX} constitutes undefined behavior. \sa empty(), isEmpty(), isNull(), size() */ /*! \fn QUtf8StringView::operator[](qsizetype n) const Returns the code point at position \a n in this string view. The behavior is undefined if \a n is negative or not less than size(). \sa at(), front(), back() */ /*! \fn QUtf8StringView::at(qsizetype n) const Returns the code point at position \a n in this string view. The behavior is undefined if \a n is negative or not less than size(). \sa operator[](), front(), back() */ /*! \fn QUtf8StringView::front() const Returns the first code point in the string. Same as first(). This function is provided for STL compatibility. \warning Calling this function on an empty string view constitutes undefined behavior. \sa back() */ /*! \fn QUtf8StringView::back() const Returns the last code point in the string. Same as last(). This function is provided for STL compatibility. \warning Calling this function on an empty string view constitutes undefined behavior. \sa front() */ /*! \fn QUtf8StringView::mid(qsizetype start, qsizetype length) const Returns the substring of length \a length starting at position \a start in this object. \obsolete Use sliced() instead in new code. Returns an empty string view if \a start exceeds the length of the string. If there are less than \a length code points available in the string starting at \a start, or if \a length is negative (default), the function returns all code points that are available from \a start. \sa first(), last(), sliced(), chopped(), chop(), truncate() */ /*! \fn QUtf8StringView::left(qsizetype length) const \obsolete Use first() instead in new code. Returns the substring of length \a length starting at position 0 in this object. The entire string is returned if \a length is greater than or equal to size(), or less than zero. \sa first(), last(), sliced(), startsWith(), chopped(), chop(), truncate() */ /*! \fn QUtf8StringView::right(qsizetype length) const \obsolete Use last() instead in new code. Returns the substring of length \a length starting at position size() - \a length in this object. The entire string is returned if \a length is greater than or equal to size(), or less than zero. \sa first(), last(), sliced(), endsWith(), chopped(), chop(), truncate() */ /*! \fn QUtf8StringView::first(qsizetype n) const Returns a string view that contains the first \a n code points of this string. \note The behavior is undefined when \a n < 0 or \a n > size(). \sa last(), sliced(), startsWith(), chopped(), chop(), truncate() */ /*! \fn QUtf8StringView::last(qsizetype n) const Returns a string view that contains the last \a n code points of this string. \note The behavior is undefined when \a n < 0 or \a n > size(). \sa first(), sliced(), endsWith(), chopped(), chop(), truncate() */ /*! \fn QUtf8StringView::sliced(qsizetype pos, qsizetype n) const Returns a string view containing \a n code points of this string view, starting at position \a pos. \note The behavior is undefined when \a pos < 0, \a n < 0, or \a pos + \a n > size(). \sa first(), last(), chopped(), chop(), truncate() */ /*! \fn QUtf8StringView::sliced(qsizetype pos) const Returns a string view starting at position \a pos in this object, and extending to its end. \note The behavior is undefined when \a pos < 0 or \a pos > size(). \sa first(), last(), chopped(), chop(), truncate() */ /*! \fn QUtf8StringView::chopped(qsizetype length) const Returns the substring of length size() - \a length starting at the beginning of this object. Same as \c{first(size() - length)}. \note The behavior is undefined when \a length < 0 or \a length > size(). \sa sliced(), first(), last(), chop(), truncate() */ /*! \fn QUtf8StringView::truncate(qsizetype length) Truncates this string view to \a length code points. Same as \c{*this = first(length)}. \note The behavior is undefined when \a length < 0 or \a length > size(). \sa sliced(), first(), last(), chopped(), chop() */ /*! \fn QUtf8StringView::chop(qsizetype length) Truncates this string view by \a length code points. Same as \c{*this = first(size() - length)}. \note The behavior is undefined when \a length < 0 or \a length > size(). \sa sliced(), first(), last(), chopped(), truncate() */ /*! \fn QUtf8StringView::trimmed() const Strips leading and trailing whitespace and returns the result. Whitespace means any code point for which QChar::isSpace() returns \c true. This includes the ASCII characters '\\t', '\\n', '\\v', '\\f', '\\r', and ' '. */ /*! \fn template qToUtf8StringViewIgnoringNull(const QStringLike &s); \relates QUtf8StringView \internal Convert \a s to a QUtf8StringView 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 QByteArray to a QUtf8StringView, if null QByteArrays can legitimately be treated as empty ones. \sa QByteArray::isNull(), QUtf8StringView */