QStringView Class

The https:// class provides a unified view on UTF-16 strings with a read-only subset of the https:// API.

This class was introduced in Qt 5.10.

All functions in this class are https://.

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Publié le 27 décembre 2024 - Mis à jour le 27 décembre 2024

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QStringView Class▲

Header: QStringView
Since: Qt 5.10
qmake: QT += core
Group: QStringView is part of tools, string-processing

Detailed Description▲

A https:// references a contiguous portion of a UTF-16 string it does not own. It acts as an interface type to all kinds of UTF-16 string, without the need to construct a https:// first.

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

https:// is designed as an interface type; its main use-case is as a function parameter type. When QStringViews are used as automatic variables or data members, care must be taken to ensure that the referenced string data (for example, owned by a https://) 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-16 string data sources. One function accepting https:// thus replaces three function overloads (taking https://, https://, and (const QChar*, int)), while at the same time enabling even more string data sources to be passed to the function, such as u"Hello World", a char16_t string literal.

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

Sélectionnez

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

If you want to give your users maximum freedom in what strings they can pass to your function, accompany the https:// overload with overloads for

QChar: this overload can delegate to the https:// version:
Sélectionnez
```
    void fun(QChar ch) { fun(QStringView(&amp;ch, 1)); }
```
even though, for technical reasons, https:// cannot provide a https:// constructor by itself.
QString: if you store an unmodified copy of the string and thus would like to take advantage of https://'s implicit sharing.
https://: if you can implement the function without converting the https:// to UTF-16 first; users expect a function overloaded on https:// to perform strictly less memory allocations than the semantically equivalent call of the https:// version, involving construction of a https:// from the https://.

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, but since it stores data as char16_t, iteration is not constexpr (casts from const char16_t* to const QChar*, which is not allowed in constexpr functions). You can use an indexed loop and/or https://() in constexpr contexts instead.

We strongly discourage the use of https://<https://>, because https:// is a very inefficient container for QStringViews (it would heap-allocate every element). Use https:// (or std::vector) to hold QStringViews instead.

Member Type Documentation▲

QStringView::const_iterator▲

This typedef provides an STL-style const iterator for https://.

QStringView::const_pointer▲

Alias for value_type *. Provided for compatibility with the STL.

QStringView::const_reference▲

Alias for value_type &. Provided for compatibility with the STL.

QStringView::const_reverse_iterator▲

This typedef provides an STL-style const reverse iterator for https://.

QStringView::difference_type▲

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

QStringView::iterator▲

This typedef provides an STL-style const iterator for https://.

https:// does not support mutable iterators, so this is the same as https://.

QStringView::pointer▲

Alias for value_type *. Provided for compatibility with the STL.

https:// does not support mutable pointers, so this is the same as https://.

QStringView::reference▲

Alias for value_type &. Provided for compatibility with the STL.

https:// does not support mutable references, so this is the same as https://.

QStringView::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://.

QStringView::size_type▲

Alias for qsizetype. Provided for compatibility with the STL.

Unlike other Qt classes, https:// uses qsizetype as its size_type, to allow accepting data from std::basic_string without truncation. The Qt API functions, for example https://(), return int, while the STL-compatible functions, for example https://(), return size_type.

QStringView::storage_type▲

Alias for char16_t.

QStringView::value_type▲

Alias for const QChar. Provided for compatibility with the STL.

Member Function Documentation▲

[since 5.14] QString QStringView::arg(Args &&... args) const▲

Replaces occurrences of %N in this string with the corresponding argument from args. The arguments are not positional: the first of the args replaces the %N with the lowest N (all of them), the second of the args the %N with the next-lowest N etc.

Args can consist of anything that implicitly converts to https://, https:// or https://.

In addition, the following types are also supported: https://, https://.

This function was introduced in Qt 5.14.

[since 5.14] int QStringView::compare(QChar ch) const▲

[since 5.14] int QStringView::compare(QChar ch, Qt::CaseSensitivity cs) const

[since 5.14] int QStringView::compare(QLatin1String l1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns an integer that compares to zero as this string-view compares to the Latin-1 string l1, or character ch, respectively.

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

This function was introduced in Qt 5.14.

bool QStringView::startsWith(QChar ch) const▲

bool QStringView::startsWith(QChar ch, Qt::CaseSensitivity cs) const

bool QStringView::startsWith(QLatin1String l1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

bool QStringView::startsWith(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns true if this string-view starts with string-view str, Latin-1 string l1, or character ch, respectively; otherwise returns false.

If cs is https:// (the default), the search is case-sensitive; otherwise the search is case-insensitive.

bool QStringView::endsWith(QChar ch) const▲

bool QStringView::endsWith(QChar ch, Qt::CaseSensitivity cs) const

bool QStringView::endsWith(QLatin1String l1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

bool QStringView::endsWith(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns true if this string-view ends with string-view str, Latin-1 string l1, or character ch, respectively; otherwise returns false.

If cs is https:// (the default), the search is case-sensitive; otherwise the search is case-insensitive.

[since 5.14] qsizetype QStringView::indexOf(QChar c, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

[since 5.14] qsizetype QStringView::indexOf(QLatin1String l1, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

[since 5.14] qsizetype QStringView::indexOf(QStringView str, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the first occurrence of the string-view str, Latin-1 string l1, or character ch, respectively, in this string-view, searching forward from index position from. Returns -1 if str is not found.

If cs is https:// (default), the search is case sensitive; otherwise the search is case insensitive.

If from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

This function was introduced in Qt 5.14.

[since 5.14] bool QStringView::contains(QChar c, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

[since 5.14] bool QStringView::contains(QLatin1String l1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

[since 5.14] bool QStringView::contains(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns true if this string-view contains an occurrence of the string-view str, Latin-1 string l1, or character ch; otherwise returns false.

If cs is https:// (the default), the search is case-sensitive; otherwise the search is case-insensitive.

This function was introduced in Qt 5.14.

[since 5.14] qsizetype QStringView::lastIndexOf(QChar c, qsizetype from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

[since 5.14] qsizetype QStringView::lastIndexOf(QLatin1String l1, qsizetype from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

[since 5.14] qsizetype QStringView::lastIndexOf(QStringView str, qsizetype from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

Returns the index position of the last occurrence of the string-view str, Latin-1 string l1, or character ch, respectively, in this string-view, searching backward from index position from. If from is -1 (default), the search starts at the last character; if from is -2, at the next to last character and so on. Returns -1 if str is not found.

If cs is https:// (default), the search is case sensitive; otherwise the search is case insensitive.

This function was introduced in Qt 5.14.

QStringView::QStringView()▲

Constructs a null string view.

QStringView::QStringView(std::nullptr_t)▲

Constructs a null string view.

QStringView::QStringView(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: QChar, ushort, char16_t and (on platforms, such as Windows, where it is a 16-bit type) wchar_t.

QStringView::QStringView(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.

QStringView::QStringView(const Char (&)[N] string = N)▲

Constructs a string view on the character string literal string. The length is set to N-1, excluding the trailing {Char(0)}. If you need the full array, use the constructor from pointer and size instead:

Sélectionnez

    auto sv = QStringView(array, std::size(array)); // using C++17 std::size()

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. The compatible character types are: QChar, ushort, char16_t and (on platforms, such as Windows, where it is a 16-bit type) wchar_t.

QStringView::QStringView(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: QChar, ushort, char16_t and (on platforms, such as Windows, where it is a 16-bit type) wchar_t.

QStringView::QStringView(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().

QStringView::QStringView(const QStringRef &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().

QStringView::QStringView(const StdBasicString &str)▲

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

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

This constructor only participates in overload resolution if StdBasicString is an instantiation of std::basic_string with a compatible character type. The compatible character types are: QChar, ushort, char16_t and (on platforms, such as Windows, where it is a 16-bit type) wchar_t.

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

QChar QStringView::at(qsizetype n) const▲

Returns the character at position n in this string view.

The behavior is undefined if n is negative or not less than https://().

QChar QStringView::back() const▲

Returns the last character in the string. Same as https://().

This function is provided for STL compatibility.

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

QStringView::const_iterator QStringView::begin() const▲

Returns a const https:// pointing to the first character in the string.

This function is provided for STL compatibility.

QStringView::const_iterator QStringView::cbegin() const▲

Same as https://().

This function is provided for STL compatibility.

QStringView::const_iterator QStringView::cend() const▲

Same as https://().

This function is provided for STL compatibility.

void QStringView::chop(qsizetype length)▲

Truncates this string view by length characters.

Same as *this = left(size() - length).

The behavior is undefined when length < 0 or length > https://().

QStringView QStringView::chopped(qsizetype length) const▲

Returns the substring of length https://() - length starting at the beginning of this object.

Same as left(size() - length).

The behavior is undefined when length < 0 or length > https://().

[since 5.12] int QStringView::compare(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

Returns an integer that compares to zero as this string-view compares to the string-view str.

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

This function was introduced in Qt 5.12.

QStringView::const_reverse_iterator QStringView::crbegin() const▲

Same as https://().

This function is provided for STL compatibility.

QStringView::const_reverse_iterator QStringView::crend() const▲

Same as https://().

This function is provided for STL compatibility.

QStringView::const_pointer QStringView::data() const▲

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

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

bool QStringView::empty() const▲

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

This function is provided for STL compatibility.

QStringView::const_iterator QStringView::end() const▲

Returns a const https:// pointing to the imaginary character after the last character in the list.

This function is provided for STL compatibility.

QChar QStringView::first() const▲

Returns the first character in the string. Same as https://().

This function is provided for compatibility with other Qt containers.

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

QChar QStringView::front() const▲

Returns the first character in the string. Same as https://().

This function is provided for STL compatibility.

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

bool QStringView::isEmpty() const▲

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

This function is provided for compatibility with other Qt containers.

bool QStringView::isNull() const▲

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

This functions is provided for compatibility with other Qt containers.

[since 5.11] bool QStringView::isRightToLeft() const▲

Returns true if the string is read right to left.

This function was introduced in Qt 5.11.

[since 5.15] bool QStringView::isValidUtf16() const▲

Returns true if the string contains valid UTF-16 encoded data, or false otherwise.

Note that this function does not perform any special validation of the data; it merely checks if it can be successfully decoded from UTF-16. The data is assumed to be in host byte order; the presence of a BOM is meaningless.

This function was introduced in Qt 5.15.

QChar QStringView::last() const▲

Returns the last character in the string. Same as https://().

This function is provided for compatibility with other Qt containers.

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

QStringView QStringView::left(qsizetype length) const▲

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

The behavior is undefined when length < 0 or length > https://().

int QStringView::length() const▲

Same as https://(), except returns the result as an int.

This function is provided for compatibility with other Qt containers.

https:// can represent strings with more than 2³¹ characters. Calling this function on a string view for which https://() returns a value greater than INT_MAX constitutes undefined behavior.

QStringView QStringView::mid(qsizetype start) const▲

Returns the substring starting at position start in this object, and extending to the end of the string.

The behavior is undefined when start < 0 or start > https://().

QStringView QStringView::mid(qsizetype start, qsizetype length) const▲

This is an overloaded function.

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

The behavior is undefined when start < 0, length < 0, or start + length > https://().

QStringView::const_reverse_iterator QStringView::rbegin() const▲

Returns a const https:// reverse iterator pointing to the first character in the string, in reverse order.

This function is provided for STL compatibility.

QStringView::const_reverse_iterator QStringView::rend() const▲

Returns a https:// reverse iterator pointing to one past the last character in the string, in reverse order.

This function is provided for STL compatibility.

QStringView QStringView::right(qsizetype length) const▲

Returns the substring of length length starting at position https://() - length in this object.

The behavior is undefined when length < 0 or length > https://().

qsizetype QStringView::size() const▲

Returns the size of this string view, in UTF-16 code points (that is, surrogate pairs count as two for the purposes of this function, the same as in https:// and https://).

QByteArray QStringView::toLatin1() const▲

Returns a Latin-1 representation of the string as a https://.

The behavior is undefined if the string contains non-Latin1 characters.

QByteArray QStringView::toLocal8Bit() const▲

Returns a local 8-bit representation of the string as a https://.

https://() is used to perform the conversion from Unicode. If the locale's encoding could not be determined, this function does the same as https://().

The behavior is undefined if the string contains characters not supported by the locale's 8-bit encoding.

QString QStringView::toString() const▲

Returns a deep copy of this string view's data as a https://.

The return value will be the null https:// if and only if this string view is null.

https:// can store strings with more than 2³⁰ characters while https:// cannot. Calling this function on a string view for which https://() returns a value greater than INT_MAX / 2 constitutes undefined behavior.

QVector<uint> QStringView::toUcs4() const▲

Returns a UCS-4/UTF-32 representation of the string as a https://<uint>.

UCS-4 is a Unicode codec and therefore it is lossless. All characters from this string will be encoded in UCS-4. Any invalid sequence of code units in this string is replaced by the Unicode replacement character (https://, which corresponds to U+FFFD).

The returned vector is not 0-terminated.

QByteArray QStringView::toUtf8() const▲

Returns a UTF-8 representation of the string as a https://.

UTF-8 is a Unicode codec and can represent all characters in a Unicode string like https://.

[since 5.14] int QStringView::toWCharArray(wchar_t *array) const▲

Transcribes this string into the given array.

The caller is responsible for ensuring array is large enough to hold the wchar_t encoding of this string (allocating the array with the same length as the string is always sufficient). The array is encoded in UTF-16 on platforms where wchar_t is 2 bytes wide (e.g. Windows); otherwise (Unix systems), wchar_t is assumed to be 4 bytes wide and the data is written in UCS-4.

This function writes no null terminator to the end of array.

Returns the number of wchar_t entries written to array.

This function was introduced in Qt 5.14.

QStringView QStringView::trimmed() const▲

Strips leading and trailing whitespace and returns the result.

Whitespace means any character for which https://() returns true. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.

void QStringView::truncate(qsizetype length)▲

Truncates this string view to length length.

Same as *this = left(length).

The behavior is undefined when length < 0 or length > https://().

const QStringView::storage_type *QStringView::utf16() const▲

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

storage_type is char16_t.

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

QChar QStringView::operator[](qsizetype n) const▲

Returns the character at position n in this string view.

The behavior is undefined if n is negative or not less than https://().

Related Non-Members▲

[since 5.10] uint qHash(QStringView key, uint seed = 0)▲

Returns the hash value for the key, using seed to seed the calculation.

This function was introduced in Qt 5.10.

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QStringView Class

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QStringView Class▲

Detailed Description▲

See Also▲

Member Type Documentation▲

QStringView::const_iterator▲

See Also▲

QStringView::const_pointer▲

QStringView::const_reference▲

QStringView::const_reverse_iterator▲

See Also▲

QStringView::difference_type▲

QStringView::iterator▲

See Also▲

QStringView::pointer▲

QStringView::reference▲

QStringView::reverse_iterator▲

See Also▲

QStringView::size_type▲

QStringView::storage_type▲

QStringView::value_type▲

Member Function Documentation▲

[since 5.14] QString QStringView::arg(Args &&... args) const▲

See Also▲

[since 5.14] int QStringView::compare(QChar ch) const▲

See Also▲

bool QStringView::startsWith(QChar ch) const▲

See Also▲

bool QStringView::endsWith(QChar ch) const▲

See Also▲

[since 5.14] qsizetype QStringView::indexOf(QChar c, qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

See Also▲

[since 5.14] bool QStringView::contains(QChar c, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

See Also▲

[since 5.14] qsizetype QStringView::lastIndexOf(QChar c, qsizetype from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

See Also▲

QStringView::QStringView()▲

See Also▲

QStringView::QStringView(std::nullptr_t)▲

See Also▲

QStringView::QStringView(const Char *str, qsizetype len)▲

QStringView::QStringView(const Char *first, const Char *last)▲

QStringView::QStringView(const Char (&)[N] string = N)▲

QStringView::QStringView(const Char *str)▲

QStringView::QStringView(const QString &str)▲

QStringView::QStringView(const QStringRef &str)▲

QStringView::QStringView(const StdBasicString &str)▲

See Also▲

QChar QStringView::at(qsizetype n) const▲

See Also▲

QChar QStringView::back() const▲

See Also▲

QStringView::const_iterator QStringView::begin() const▲

See Also▲

QStringView::const_iterator QStringView::cbegin() const▲

See Also▲

QStringView::const_iterator QStringView::cend() const▲

See Also▲

void QStringView::chop(qsizetype length)▲

See Also▲

QStringView QStringView::chopped(qsizetype length) const▲

See Also▲

[since 5.12] int QStringView::compare(QStringView str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const▲

See Also▲

QStringView::const_reverse_iterator QStringView::crbegin() const▲

See Also▲

QStringView::const_reverse_iterator QStringView::crend() const▲

See Also▲

QStringView::const_pointer QStringView::data() const▲

See Also▲

bool QStringView::empty() const▲

See Also▲

QStringView::const_iterator QStringView::end() const▲

See Also▲

QChar QStringView::first() const▲

See Also▲

QChar QStringView::front() const▲

QStringView::QStringView(const Char first, const Char last)▲