QUtf8StringView Class▲
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Header: QUtf8StringView
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Since: Qt 6.0
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CMake:
find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core)
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qmake: QT += core
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Group: QUtf8StringView is part of tools, string-processing
Detailed Description▲
A https:// 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 https:// or https:// first.
The UTF-8 string may be represented as an array (or an array-compatible data-structure such as std::basic_string, etc.) of char8_t, char, signed char or unsigned char.
https:// 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 https:// on all code paths, lest the string view ends up referencing deleted data.
When used as an interface type, https:// allows a single function to accept a wide variety of UTF-8 string data sources. One function accepting https:// thus replaces several function overloads (taking e.g. https://), 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 (C++20) or char (C++17) string literal. The char8_t incompatibility between C++17 and C++20 goes away when using https://.
Like all views, QUtf8StringViews should be passed by value, not by reference-to-const:
void myfun1(QUtf8StringView sv); // preferred
void myfun2(const QUtf8StringView &sv); // compiles and works, but slowerIf you want to give your users maximum freedom in what strings they can pass to your function, consider using https:// instead.
https:// can also be used as the return value of a function. If you call a function returning https://, take extra care to not keep the https:// 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 https://() to convert the https:// into a https://.
https:// is a Literal Type.
Compatible Character Types▲
https:// accepts strings over a variety of character types:
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char (both signed and unsigned)
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char8_t (C++20 only)
Sizes and Sub-Strings▲
All sizes and positions in https:// functions are in UTF-8 code points (that is, UTF-8 multibyte sequences count as two, three or four, depending on their length). https:// does not an attempt to detect or prevent slicing right through UTF-8 multibyte sequences. This is similar to the situation with https:// and surrogate pairs.
C++20, char8_t, and QUtf8StringView▲
In C++20, u8"" string literals changed their type from const char[] to const char8_t[]. If Qt 6 could have depended on C++20, https:// would store char8_t natively, and the following functions and aliases would use (pointers to) char8_t:
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https://, https://, etc
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https://(), https://(), https://(), etc
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https://(), https://(), https://(), operator[]()
This is what https:// 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 https:// classes, in different (inline) namespaces. The first, in namespace q_no_char8_t, has a https:// of const char and is universally available. The second, in namespace q_has_char8_t, has a https:// of const char8_t and is only available when compiling in C++20 mode.
q_no_char8_t is an inline namespace regardless of C++ edition, to avoid accidental binary incompatibilities. To use the char8_t version, you need to name it explicitly with q_has_char8_t::QUtf8StringView.
Internally, both are instantiations of the same template class, QBasicUtf8StringView. Please do not use the template class's name in your source code.
See Also▲
See also https://, https://, https://
Member Type Documentation▲
QUtf8StringView::const_iterator▲
This typedef provides an STL-style const iterator for https://.
See Also▲
See also https://, https://
QUtf8StringView::const_pointer▲
Alias for value_type *. Provided for compatibility with the STL.
QUtf8StringView::const_reference▲
Alias for value_type &. Provided for compatibility with the STL.
QUtf8StringView::const_reverse_iterator▲
This typedef provides an STL-style const reverse iterator for https://.
See Also▲
See also https://, https://
QUtf8StringView::difference_type▲
Alias for std::ptrdiff_t. Provided for compatibility with the STL.
QUtf8StringView::iterator▲
This typedef provides an STL-style const iterator for https://.
https:// does not support mutable iterators, so this is the same as https://.
See Also▲
See also https://, https://
QUtf8StringView::pointer▲
Alias for value_type *. Provided for compatibility with the STL.
https:// does not support mutable pointers, so this is the same as https://.
QUtf8StringView::reference▲
Alias for value_type &. Provided for compatibility with the STL.
https:// does not support mutable references, so this is the same as https://.
QUtf8StringView::reverse_iterator▲
This typedef provides an STL-style const reverse iterator for https://.
https:// does not support mutable reverse iterators, so this is the same as https://.
See Also▲
See also https://, https://
QUtf8StringView::size_type▲
Alias for qsizetype. Provided for compatibility with the STL.
[alias] QUtf8StringView::storage_type▲
Alias for char.
QUtf8StringView::value_type▲
Alias for const char. Provided for compatibility with the STL.
Member Function Documentation▲
[since 6.5] int QUtf8StringView::compare(QLatin1StringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲
[since 6.5] int QUtf8StringView::compare(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const
[since 6.5] int QUtf8StringView::compare(QUtf8StringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const
Compares this string view with str and returns a negative integer if this string view is less than str, a positive integer if it is greater than str, and zero if they are equal.
If cs is https:// (the default), the comparison is case-sensitive; otherwise the comparison is case-insensitive.
This function was introduced in Qt 6.5.
[constexpr] QUtf8StringView::QUtf8StringView()▲
[constexpr] QUtf8StringView::QUtf8StringView(std::nullptr_t)▲
[constexpr] QUtf8StringView::QUtf8StringView(const Char *str, qsizetype len)▲
Constructs a string view on str with length len.
The range [str,len) must remain valid for the lifetime of this string view object.
Passing nullptr as str is safe if len is 0, too, and results in a null string view.
The behavior is undefined if len is negative or, when positive, if str is nullptr.
This constructor only participates in overload resolution if Char is a compatible character type. The compatible character types are: char8_t, char, signed char and unsigned char.
[constexpr] QUtf8StringView::QUtf8StringView(const Char *first, const Char *last)▲
Constructs a string view on first with length (last - first).
The range [first,last) must remain valid for the lifetime of this string view object.
Passing \nullptr as first is safe if last is nullptr, too, and results in a null string view.
The behavior is undefined if last precedes first, or first is nullptr and last is not.
This constructor only participates in overload resolution if Char is a compatible character type. The compatible character types are: char8_t, char, signed char and unsigned char.
[constexpr] QUtf8StringView::QUtf8StringView(const Char (&)[N] string = N)▲
Constructs a string view on the character string literal string. The view covers the array until the first Char(0) is encountered, or N, whichever comes first. If you need the full array, use https://() instead.
string must remain valid for the lifetime of this string view object.
This constructor only participates in overload resolution if string is an actual array and if Char is a compatible character type. The compatible character types are: char8_t, char, signed char and unsigned char.
See Also▲
See also https://()
[constexpr] QUtf8StringView::QUtf8StringView(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. The compatible character types are: char8_t, char, signed char and unsigned char.
[constexpr] QUtf8StringView::QUtf8StringView(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 compatible character types are: char8_t, char, signed char and unsigned char.
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▲
See also https://(), https://()
[constexpr] QUtf8StringView::storage_type QUtf8StringView::at(qsizetype n) const▲
Returns the code point at position n in this string view.
The behavior is undefined if n is negative or not less than https://().
See Also▲
See also https://(), https://(), https://()
[constexpr] QUtf8StringView::storage_type QUtf8StringView::back() const▲
Returns the last code point in the string view. Same as https://().
This function is provided for STL compatibility.
Calling this function on an empty string view constitutes undefined behavior.
See Also▲
See also https://()
QUtf8StringView::const_iterator QUtf8StringView::begin() const▲
Returns a const https:// pointing to the first code point in the string view.
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://(), https://()
QUtf8StringView::const_iterator QUtf8StringView::cbegin() const▲
Same as https://().
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://(), https://()
QUtf8StringView::const_iterator QUtf8StringView::cend() const▲
Same as https://().
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://()
[constexpr] void QUtf8StringView::chop(qsizetype n)▲
Truncates this string view by n code points.
Same as *this = first(size() - n).
The behavior is undefined when n < 0 or n > https://().
See Also▲
See also https://(), https://(), https://(), https://(), https://()
[constexpr] QUtf8StringView QUtf8StringView::chopped(qsizetype n) const▲
Returns the substring of length https://() - n starting at the beginning of this object.
Same as first(size() - n).
The behavior is undefined when n < 0 or n > https://().
See Also▲
See also https://(), https://(), https://(), https://(), https://()
QUtf8StringView::const_reverse_iterator QUtf8StringView::crbegin() const▲
Same as https://().
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://()
QUtf8StringView::const_reverse_iterator QUtf8StringView::crend() const▲
Same as https://().
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://()
QUtf8StringView::const_pointer QUtf8StringView::data() const▲
Returns a const pointer to the first code point in the string view.
The character array represented by the return value is not null-terminated.
See Also▲
See also https://(), https://(), utf8()
[constexpr] bool QUtf8StringView::empty() const▲
Returns whether this string view is empty - that is, whether size() == 0.
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://(), https://()
QUtf8StringView::const_iterator QUtf8StringView::end() const▲
Returns a const https:// pointing to the imaginary code point after the last code point in the list.
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://()
[constexpr] QUtf8StringView QUtf8StringView::first(qsizetype n) const▲
Returns a string view that contains the first n code points of this string view.
The behavior is undefined when n < 0 or n > https://().
See Also▲
See also https://(), https://(), https://(), https://(), https://()
[static constexpr] QUtf8StringView QUtf8StringView::fromArray(const Char (&)[Size] string = Size)▲
Constructs a string view on the full character string literal string, including any trailing Char(0). If you don't want the null-terminator included in the view then you can https://() it off when you are certain it is at the end. 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.
string must remain valid for the lifetime of this string view object.
This function will work with any array literal if Char is a compatible character type. The compatible character types are: char8_t, char, signed char and unsigned char.
[constexpr] QUtf8StringView::storage_type QUtf8StringView::front() const▲
Returns the first code point in the string view. Same as https://().
This function is provided for STL compatibility.
Calling this function on an empty string view constitutes undefined behavior.
See Also▲
See also https://()
[constexpr] bool QUtf8StringView::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▲
See also https://(), https://(), https://(), https://()
[constexpr] bool QUtf8StringView::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▲
See also https://(), https://(), https://(), https://()
[since 6.3] bool QUtf8StringView::isValidUtf8() const▲
Returns true if this string contains valid UTF-8 encoded data, or false otherwise.
This function was introduced in Qt 6.3.
[constexpr] QUtf8StringView QUtf8StringView::last(qsizetype n) const▲
Returns a string view that contains the last n code points of this string view.
The behavior is undefined when n < 0 or n > https://().
See Also▲
See also https://(), https://(), https://(), https://(), https://()
[constexpr] qsizetype QUtf8StringView::length() const▲
Same as https://().
This function is provided for compatibility with other Qt containers.
See Also▲
See also https://(), https://(), https://(), https://()
QUtf8StringView::const_reverse_iterator QUtf8StringView::rbegin() const▲
Returns a const https:// reverse iterator pointing to the first code point in the string view, in reverse order.
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://()
QUtf8StringView::const_reverse_iterator QUtf8StringView::rend() const▲
Returns a https:// reverse iterator pointing to one past the last code point in the string view, in reverse order.
This function is provided for STL compatibility.
See Also▲
See also https://(), https://(), https://()
[constexpr] 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 https:// and https://).
See Also▲
See also https://(), https://(), https://(), https://()
[constexpr] QUtf8StringView QUtf8StringView::sliced(qsizetype pos) const▲
Returns a string view starting at position pos in this object, and extending to its end.
The behavior is undefined when pos < 0 or pos > https://().
See Also▲
See also https://(), https://(), https://(), https://(), https://()
[constexpr] QUtf8StringView QUtf8StringView::sliced(qsizetype pos, qsizetype n) const▲
Returns a string view containing n code points of this string view, starting at position pos.
The behavior is undefined when pos < 0, n < 0, or pos + n > https://().
See Also▲
See also https://(), https://(), https://(), https://(), https://()
QString QUtf8StringView::toString() const▲
Returns a deep copy of this string view's data as a https://.
The return value will be a null https:// if and only if this string view is null.
[constexpr] void QUtf8StringView::truncate(qsizetype n)▲
Truncates this string view to n code points.
Same as *this = first(n).
The behavior is undefined when n < 0 or n > https://().
See Also▲
See also https://(), https://(), https://(), https://(), https://()
[constexpr] QUtf8StringView::storage_type QUtf8StringView::operator[](qsizetype n) const▲
Returns the code point at position n in this string view.
The behavior is undefined if n is negative or not less than https://().
See Also▲
See also https://(), https://(), https://()
Obsolete Members for QUtf8StringView▲
The following members of class https:// are deprecated. We strongly advise against using them in new code.
Obsolete Member Function Documentation▲
[constexpr] QUtf8StringView QUtf8StringView::left(qsizetype n) const▲
This function is deprecated. We strongly advise against using it in new code.
Use https://() 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 https://(), or less than zero.
See Also▲
See also https://(), https://(), https://(), https://(), https://(), https://()
[constexpr] QUtf8StringView QUtf8StringView::mid(qsizetype pos, qsizetype n = -1) const▲
This function is deprecated. We strongly advise against using it in new code.
Returns the substring of length n starting at position pos in this object.
Use https://() 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▲
See also https://(), https://(), https://(), https://(), https://(), https://()
[constexpr] QUtf8StringView QUtf8StringView::right(qsizetype n) const▲
This function is deprecated. We strongly advise against using it in new code.
Use https://() instead in new code.
Returns the substring of length n starting at position https://() - n in this object.
The entire string view is returned if n is greater than or equal to https://(), or less than zero.
See Also▲
See also https://(), https://(), https://(), https://(), https://(), https://()