QByteArrayView Class

The QByteArrayView class provides a view on an array of bytes with a read-only subset of the QByteArray API. More...

Header:	#include <QByteArrayView>
CMake:	find_package(Qt6 COMPONENTS Core REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake:	QT += core
Since:	Qt 6.0

• List of all members, including inherited members
• Obsolete members

Note: All functions in this class are reentrant.

Public Types

	const_iterator
	const_pointer
	const_reference
	const_reverse_iterator
	difference_type
	iterator
	pointer
	reference
	reverse_iterator
	size_type
	storage_type
	value_type

Public Functions

	QByteArrayView(const char (&)[Size] data = Size)
	QByteArrayView(const Container &c)
	QByteArrayView(const QByteArray &byteArray)
	QByteArrayView(const Byte *data)
	QByteArrayView(const Byte *first, const Byte *last)
	QByteArrayView(const Byte *data, qsizetype len)
	QByteArrayView(std::nullptr_t)
	QByteArrayView()
char	at(qsizetype n) const
char	back() const
QByteArrayView::const_iterator	begin() const
QByteArrayView::const_iterator	cbegin() const
QByteArrayView::const_iterator	cend() const
void	chop(qsizetype length)
QByteArrayView	chopped(qsizetype length) const
QByteArrayView::const_pointer	constData() const
bool	contains(QByteArrayView bv) const
bool	contains(char ch) const
qsizetype	count(QByteArrayView bv) const
qsizetype	count(char ch) const
QByteArrayView::const_reverse_iterator	crbegin() const
QByteArrayView::const_reverse_iterator	crend() const
QByteArrayView::const_pointer	data() const
bool	empty() const
QByteArrayView::const_iterator	end() const
bool	endsWith(QByteArrayView bv) const
bool	endsWith(char ch) const
QByteArrayView	first(qsizetype n) const
char	front() const
qsizetype	indexOf(QByteArrayView bv, qsizetype from = 0) const
qsizetype	indexOf(char ch, qsizetype from = 0) const
bool	isEmpty() const
bool	isNull() const
QByteArrayView	last(qsizetype n) const
qsizetype	lastIndexOf(QByteArrayView bv, qsizetype from = -1) const
qsizetype	lastIndexOf(char ch, qsizetype from = -1) const
QByteArrayView::const_reverse_iterator	rbegin() const
QByteArrayView::const_reverse_iterator	rend() const
qsizetype	size() const
QByteArrayView	sliced(qsizetype pos) const
QByteArrayView	sliced(qsizetype pos, qsizetype n) const
bool	startsWith(QByteArrayView bv) const
bool	startsWith(char ch) const
QByteArray	toByteArray() const
void	truncate(qsizetype length)
char	operator[](qsizetype n) const

Static Public Members

QByteArrayView

fromArray(const Byte (&)[Size] data = Size)

Detailed Description

A QByteArrayView references a contiguous portion of raw bytes it does not own. It acts as an interface type to all kinds of byte-array-like data, without the need to construct a QByteArray first.

The byte array data may be represented as an array (or an array-compatible data-structure such as QByteArray, std::basic_string, etc.) of char, signed char, unsigned char or std::byte.

QByteArrayView is designed as an interface type; its main use-case is as a function parameter type. When QByteArrayViews are used as automatic variables or data members, care must be taken to ensure that the referenced data (for example, owned by a QByteArray) outlives the QByteArrayView on all code paths, lest the byte array view ends up referencing deleted data.

When used as an interface type, QByteArrayView allows a single function to accept a wide variety of byte-array-like data sources. One function accepting QByteArrayView thus replaces several function overloads (taking, for example, QByteArray, const char *, etc.) while at the same time enabling even more byte array data sources to be passed to the function.

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

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

If you want to give your users maximum freedom in what type of data they can pass to your function, accompany the QByteArrayView overload with overloads for

• char: this overload can delegate to the QByteArrayView version:

      void fun(QByteArrayView bv);
      void fun(char ch) { fun(QByteArrayView(&ch, 1)); }

  even though, for technical reasons, QByteArrayView cannot provide a char constructor by itself.

• QByteArray: if you store an unmodified copy of the byte array and thus would like to take advantage of QByteArray's implicit sharing.

QByteArrayView can also be used as the return value of a function. If you call a function returning QByteArrayView, take extra care to not keep the QByteArrayView around longer than the function promises to keep the referenced data alive. If in doubt, obtain a strong reference to the data by calling toByteArray() to convert the QByteArrayView into a QByteArray.

Compatible Byte Types

QByteArrayView can be constructed on any container of bytes, where the byte type is one of:

• char (both signed and unsigned)
• std::byte

See also QByteArray and QStringView.

Member Type Documentation

QByteArrayView::const_iterator

This typedef provides an STL-style const iterator for QByteArrayView.

See also iterator and const_reverse_iterator.

QByteArrayView::const_pointer

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

QByteArrayView::const_reference

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

QByteArrayView::const_reverse_iterator

This typedef provides an STL-style const reverse iterator for QByteArrayView.

See also reverse_iterator and const_iterator.

QByteArrayView::difference_type

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

QByteArrayView::iterator

This typedef provides an STL-style const iterator for QByteArrayView.

QByteArrayView does not support mutable iterators, so this is the same as const_iterator.

See also const_iterator and reverse_iterator.

QByteArrayView::pointer

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

QByteArrayView does not support mutable pointers, so this is the same as const_pointer.

QByteArrayView::reference

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

QByteArrayView does not support mutable references, so this is the same as const_reference.

QByteArrayView::reverse_iterator

This typedef provides an STL-style const reverse iterator for QByteArrayView.

QByteArrayView does not support mutable reverse iterators, so this is the same as const_reverse_iterator.

See also const_reverse_iterator and iterator.

QByteArrayView::size_type

Alias for qsizetype. Provided for compatibility with the STL.

QByteArrayView::storage_type

Alias for char.

QByteArrayView::value_type

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

Member Function Documentation

Returns the index position of either the start of the last occurrence of the sequence of bytes viewed by bv or the last occurrence of byte ch, respectively, in this byte array view, searching forward from index position from. If from is -1 (the default), the search starts from the end of the byte array view. Returns -1 if no match is found.

See also indexOf() and contains().

Returns true if this byte array view contains an occurrence of the sequence of bytes viewed by bv or character ch, respectively; otherwise returns false.

See also indexOf() and lastIndexOf().

Returns the index position of either the start of the first occurrence of the sequence of bytes viewed by bv or the first occurrence of byte ch, respectively, in this byte array view, searching forward from index position from.Returns -1 if no match is found.

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

See also lastIndexOf() and contains().

Returns true if this byte array view ends with byte array view bv or character ch, respectively; otherwise returns false.

See also startsWith().

Returns true if this byte array view starts with byte array view bv or character ch, respectively; otherwise returns false.

See also endsWith().

template <size_t Size> QByteArrayView::QByteArrayView(const char (&)[Size] data = Size)

Constructs a byte array view on the char array data. The view covers the array until the first '\0' is encountered, or Size, whichever comes first. If you need the full array, use fromArray() instead.

data must remain valid for the lifetime of this byte array view object.

Note: This constructor is only available for char array literals. The reasoning behind that is for compatibility with C-libraries which predefine "large-enough" arrays, but only use some of the preallocated space. To support this in an intuitive way in an implicit constructor overload, we need to stop at the first char(0). This is logical for a char array, but not for a std::byte array.

See also fromArray.

template <typename Container, if_compatible_container<Container>> QByteArrayView::QByteArrayView(const Container &c)

Constructs a byte array view on the array-like container c. The length and data are set via std::size(c) and std::data(c) respectively.

The container's data must remain valid for the lifetime of this byte array view object.

This constructor participates in overload resolution if c is any contiguous container container with elements of a compatible byte type.

See also Compatible Byte Types.

QByteArrayView::QByteArrayView(const QByteArray &byteArray)

Constructs a byte array view on byteArray.

byteArray.data() must remain valid for the lifetime of this byte array view object.

The byte array view will be null if and only if byteArray.isNull().

template <typename Byte> QByteArrayView::QByteArrayView(const Byte *data)

Constructs a byte array view on data. The length is determined by scanning for the first Byte(0).

data must remain valid for the lifetime of this byte array view object.

Passing nullptr as data is safe and results in a null byte array view.

This constructor only participates in overload resolution if data is not an array and if Byte is a compatible byte type.

See also Compatible Byte Types.

template <typename Byte, if_compatible_byte<Byte>> QByteArrayView::QByteArrayView(const Byte *first, const Byte *last)

Constructs a byte array view on first with length (last - first).

The range [first,last) must remain valid for the lifetime of this QByteArrayView.

Passing \nullptr as first is safe if last is nullptr, too, and results in a null byte array 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 Byte is a compatible byte type.

See also Compatible Byte Types.

template <typename Byte, if_compatible_byte<Byte>> QByteArrayView::QByteArrayView(const Byte *data, qsizetype len)

Constructs a byte array view on data with length len.

The range [data,len) must remain valid for the lifetime of this QByteArrayView.

Passing nullptr as data is safe if len is 0, too, and results in a null byte array view.

The behavior is undefined if len is negative or, when positive, if data is nullptr.

This constructor only participates in overload resolution if Byte is a compatible byte type.

See also Compatible Byte Types.

QByteArrayView::QByteArrayView(std::nullptr_t)

Constructs a null byte array view.

See also isNull().

QByteArrayView::QByteArrayView()

Constructs a null byte array view.

See also isNull().

char QByteArrayView::at(qsizetype n) const

Returns the character at position n in this byte array view.

The behavior is undefined if n is negative or not less than size().

See also operator[](), front(), and back().

char QByteArrayView::back() const

Returns the last byte in the byte array.

This function is provided for STL compatibility.

Warning: Calling this function on an empty byte array view constitutes undefined behavior.

See also front().

QByteArrayView::const_iterator QByteArrayView::begin() const

Returns a const STL-style iterator pointing to the first byte in the byte array.

This function is provided for STL compatibility.

See also end(), cbegin(), rbegin(), and data().

QByteArrayView::const_iterator QByteArrayView::cbegin() const

Same as begin().

This function is provided for STL compatibility.

See also cend(), begin(), crbegin(), and data().

QByteArrayView::const_iterator QByteArrayView::cend() const

Same as end().

This function is provided for STL compatibility.

See also cbegin(), end(), and crend().

void QByteArrayView::chop(qsizetype length)

Truncates this byte array view by length characters.

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

Note: The behavior is undefined when length < 0 or length > size().

See also sliced(), first(), last(), chopped(), and truncate().

QByteArrayView QByteArrayView::chopped(qsizetype length) const

Returns a copy of this byte array view that omits its last length bytes. In other words, returns a byte array view of length size() - length starting at the beginning of this object.

Same as first(size() - length).

Note: The behavior is undefined when length < 0 or length > size().

See also first(), last(), sliced(), chop(), and truncate().

QByteArrayView::const_pointer QByteArrayView::constData() const

Returns a const char pointer to the first byte in the byte array.

Note: The character array represented by the return value is not guaranteed to be null-terminated. The returned pointer is only safe to use for accessing bytes at indices that are less than this byte array view's size().

See also data(), begin(), and end().

qsizetype QByteArrayView::count(QByteArrayView bv) const

Returns the number of (potentially overlapping) occurrences of the sequence of bytes viewed by bv in this byte array view.

See also contains() and indexOf().

qsizetype QByteArrayView::count(char ch) const

This is an overloaded function.

Returns the number of occurrences of byte ch in this byte array view.

See also contains() and indexOf().

QByteArrayView::const_reverse_iterator QByteArrayView::crbegin() const

Same as rbegin().

This function is provided for STL compatibility.

See also crend(), rbegin(), and cbegin().

QByteArrayView::const_reverse_iterator QByteArrayView::crend() const

Same as rend().

This function is provided for STL compatibility.

See also crbegin(), rend(), and cend().

QByteArrayView::const_pointer QByteArrayView::data() const

Returns a const char pointer to the first byte in the byte array.

Note: The character array represented by the return value is not guaranteed to be null-terminated. The returned pointer is only safe to use for accessing bytes at indices that are less than this byte array view's size().

See also begin() and end().

bool QByteArrayView::empty() const

Returns true if this byte array view is empty - that is, size() == 0.

This function is provided for STL compatibility.

See also isEmpty(), isNull(), and size().

QByteArrayView::const_iterator QByteArrayView::end() const

Returns a const STL-style iterator pointing just after the last byte in the byte array.

This function is provided for STL compatibility.

See also begin(), cend(), and rend().

QByteArrayView QByteArrayView::first(qsizetype n) const

Returns a byte array view that points to the first n bytes of this byte array view. Equivalent to sliced(0, n).

Note: The behavior is undefined when n < 0 or n > size().

See also last(), startsWith(), chopped(), chop(), and truncate().

[static] template <typename Byte, size_t Size> QByteArrayView QByteArrayView::fromArray(const Byte (&)[Size] data = Size)

Constructs a byte array view on the array literal data. The view covers the full array. That includes the trailing null-terminator of char array literals. If you don't want the null-terminator included in the view, you can chop() it off when you are certain it is at the end. Alternatively you can use the constructor overload taking a char array literal which will create a view up to, but not including, the first null-terminator in the data.

This function will work with any array literal of a compatible byte type.

See also Compatible Byte Types and QByteArrayView.

char QByteArrayView::front() const

Returns the first byte in the byte array.

This function is provided for STL compatibility.

Warning: Calling this function on an empty byte array view constitutes undefined behavior.

See also back().

bool QByteArrayView::isEmpty() const

Returns true if this byte array view is empty - that is, size() == 0.

See also empty(), isNull(), and size().

bool QByteArrayView::isNull() const

Returns true if this byte array view is null - that is, data() == nullptr.

See also empty(), isEmpty(), and size().

QByteArrayView QByteArrayView::last(qsizetype n) const

Returns a byte array view that points to the last n bytes of this byte array view.

Note: The behavior is undefined when n < 0 or n > size().

See also first(), endsWith(), chopped(), chop(), and truncate().

QByteArrayView::const_reverse_iterator QByteArrayView::rbegin() const

Returns a const STL-style reverse iterator pointing to the first byte in the byte array, in reverse order.

This function is provided for STL compatibility.

See also rend(), crbegin(), and begin().

QByteArrayView::const_reverse_iterator QByteArrayView::rend() const

Returns a STL-style reverse iterator pointing to one past the last byte in the byte array, in reverse order.

This function is provided for STL compatibility.

See also rbegin(), crend(), and end().

qsizetype QByteArrayView::size() const

Returns the number of bytes in this byte array view.

See also empty(), isEmpty(), and isNull().

QByteArrayView QByteArrayView::sliced(qsizetype pos) const

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

Note: The behavior is undefined when pos < 0 or pos > size().

See also first(), last(), chopped(), chop(), and truncate().

QByteArrayView QByteArrayView::sliced(qsizetype pos, qsizetype n) const

Returns a byte array view that points to n bytes of this byte array view, starting at position pos.

Note: The behavior is undefined when pos < 0, n < 0, or pos + n > size().

See also first(), last(), chopped(), chop(), and truncate().

QByteArray QByteArrayView::toByteArray() const

Returns a deep copy of this byte array view's data as a QByteArray.

The return value will be a null QByteArray if and only if this byte array view is null.

Warning: QByteArrayView can store data with more than 2³¹ bytes while QByteArray cannot. Calling this function on a byte array view for which size() returns a value greater than INT_MAX / 2 constitutes undefined behavior.

void QByteArrayView::truncate(qsizetype length)

Truncates this byte array view to length length.

Same as *this = first(length).

Note: The behavior is undefined when length < 0 or length > size().

See also first(), last(), sliced(), chopped(), and chop().

char QByteArrayView::operator[](qsizetype n) const

Returns the character at position n in this byte array view.

The behavior is undefined if n is negative or not less than size().

See also at(), front(), and back().