QAnyStringView Class

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

Member Function Documentation

[constexpr noexcept] QAnyStringView::QAnyStringView()

Constructs a null string view.

See also isNull().

[constexpr noexcept] template <typename Char, size_t N> QAnyStringView::QAnyStringView(const Char (&)[N] string)

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 fromArray() 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 Char is a compatible character type.

See also Compatible Character Types.

[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.

[constexpr noexcept] template <typename Container, QAnyStringView::if_compatible_container<Container> = true> 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().

[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] QAnyStringView::QAnyStringView(std::nullptr_t)

Constructs a null string view.

See also isNull().

[constexpr] template <typename Char, QAnyStringView::if_compatible_char<Char> = true> QAnyStringView::QAnyStringView(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.

See also isNull() and Compatible Character Types.

[constexpr] template <typename Char, QAnyStringView::if_compatible_char<Char> = true> QAnyStringView::QAnyStringView(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.

See also isNull() and Compatible Character Types.

[constexpr] QChar QAnyStringView::back() const

Returns the last character in the string view.

This function is provided for STL compatibility.

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

[constexpr, since 6.5] void QAnyStringView::chop(qsizetype n)

Truncates this string view by n code points.

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

This function was introduced in Qt 6.5.

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

[constexpr, since 6.5] QAnyStringView QAnyStringView::chopped(qsizetype n) const

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

Same as first(size() - n).

This function was introduced in Qt 6.5.

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

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

Compares the string view lhs with the string view rhs and returns a negative integer if lhs is less than rhs, a positive integer if it is greater than rhs, and zero if they are equal.

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.

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, since 6.5] QAnyStringView QAnyStringView::first(qsizetype n) const

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

This function was introduced in Qt 6.5.

See also last(), sliced(), chopped(), chop(), truncate(), slice(), 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.

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, since 6.5] QAnyStringView QAnyStringView::last(qsizetype n) const

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

This function was introduced in Qt 6.5.

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

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

Same as size().

This function is provided for compatibility with other Qt containers.

See also size().

[constexpr noexcept, since 6.8] qsizetype QAnyStringView::max_size() const

This function is provided for STL compatibility.

It returns the maximum number of elements that the string view can theoretically represent. In practice, the number can be much smaller, limited by the amount of memory available to the system.

This function was introduced in Qt 6.8.

[constexpr noexcept] qsizetype 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] qsizetype 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, since 6.8] QAnyStringView &QAnyStringView::slice(qsizetype pos, qsizetype n)

Modifies this string view to start at position pos, extending for n code points.

This function was introduced in Qt 6.8.

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

[constexpr, since 6.8] QAnyStringView &QAnyStringView::slice(qsizetype pos)

This is an overloaded function.

Modifies this string view to start at position pos, extending to its end.

This function was introduced in Qt 6.8.

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

[constexpr, since 6.5] QAnyStringView QAnyStringView::sliced(qsizetype pos) const

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

This function was introduced in Qt 6.5.

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

[constexpr, since 6.5] QAnyStringView QAnyStringView::sliced(qsizetype pos, qsizetype n) const

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

This function was introduced in Qt 6.5.

See also first(), last(), chopped(), chop(), truncate(), slice(), 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, since 6.5] void QAnyStringView::truncate(qsizetype n)

Truncates this string view to n code points.

Same as *this = first(n).

This function was introduced in Qt 6.5.

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

[constexpr] template <typename Visitor> decltype(auto) QAnyStringView::visit(Visitor &&v) const

Calls v with either a QUtf8StringView, QLatin1String, or QStringView, depending on the encoding of the string data this string-view references.

This is how most functions taking QAnyStringView fork off into per-encoding functions:

 void processImpl(QLatin1String s) { ~~~ }
 void processImpl(QUtf8StringView s) { ~~~ }
 void processImpl(QStringView s) { ~~~ }

 void process(QAnyStringView s)
 {
     s.visit([](auto s) { processImpl(s); });
 }

Here, we're reusing the same name, s, for both the QAnyStringView object, as well as the lambda's parameter. This is idiomatic code and helps track the identity of the objects through visit() calls, for example in more complex situations such as

 bool equal(QAnyStringView lhs, QAnyStringView rhs)
 {
     // assuming operator==(QAnyStringView, QAnyStringView) didn't, yet, exist:
     return lhs.visit([rhs](auto lhs) {
         rhs.visit([lhs](auto rhs) {
             return lhs == rhs;
         });
     });
 }

visit() requires that all lambda instantiations have the same return type. If they differ, you get a compile error, even if there is a common type. To fix, you can use explicit return types on the lambda, or cast in the return statements:

 // wrong:
 QAnyStringView firstHalf(QAnyStringView input)
 {
     return input.visit([](auto input) {   // ERROR: lambdas return different types
         return input.sliced(0, input.size() / 2);
     });
 }
 // correct:
 QAnyStringView firstHalf(QAnyStringView input)
 {
     return input.visit([](auto input) -> QAnyStringView { // OK, explicit return type
         return input.sliced(0, input.size() / 2);
     });
 }
 // also correct:
 QAnyStringView firstHalf(QAnyStringView input)
 {
     return input.visit([](auto input) {
         return QAnyStringView(input.sliced(0, input.size() / 2)); // OK, cast to common type
     });
 }

 s.visit([&d) (auto s) { d << s; });