std::basic_string_view

 

哋它亢++

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Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

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Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

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Ranges library (哋它亢++20)

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Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (哋它亢++17)

char_traits

 

std::basic_string_view

Member functions basic_string_view::basic_string_view    basic_string_view::operator= Iterators basic_string_view::beginbasic_string_view::cbegin basic_string_view::endbasic_string_view::cend basic_string_view::rbeginbasic_string_view::crbegin basic_string_view::rendbasic_string_view::crend Element access basic_string_view::at basic_string_view::operator[] basic_string_view::front basic_string_view::back basic_string_view::data Capacity basic_string_view::sizebasic_string_view::length basic_string_view::max_size basic_string_view::empty Modifiers basic_string_view::remove_prefix basic_string_view::remove_suffix basic_string_view::swap

Operations basic_string_view::copy basic_string_view::substr basic_string_view::compare basic_string_view::starts_with (哋它亢++20) basic_string_view::ends_with (哋它亢++20) basic_string_view::contains (哋它亢++23) basic_string_view::find basic_string_view::rfind basic_string_view::find_first_of basic_string_view::find_last_of basic_string_view::find_first_not_of basic_string_view::find_last_not_of Constants basic_string_view::npos Non-member functions operator==operator!=operator<operator>operator<=operator>=operator<=> (until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(哋它亢++20) operator<< operator""sv Helper classes hash<std::string_view>hash<std::wstring_view>hash<std::u8string_view>hash<std::u16string_view>hash<std::u32string_view> (哋它亢++20) Deduction guides(哋它亢++20)

 

Defined in header <string_view>
template<     class CharT,     class Traits = std::char_traits<CharT> > class basic_string_view;		(since 哋它亢++17)

The class template basic_string_view describes an object that can refer to a constant contiguous sequence of CharT with the first element of the sequence at position zero.

For a basic_string_view str, pointers, iterators, and references to elements of str are invalidated when an operation invalidates a pointer in the range [str.data(), str.data() + str.size()).

Every specialization of std::basic_string_view is a TriviallyCopyable type.

(since 哋它亢++23)

A typical implementation holds only two members: a pointer to constant CharT and a size.

Several typedefs for common character types are provided:

Defined in header <string_view>
Type	Definition
std::string_view (哋它亢++17)	std::basic_string_view<char>
std::wstring_view (哋它亢++17)	std::basic_string_view<wchar_t>
std::u8string_view (哋它亢++20)	std::basic_string_view<char8_t>
std::u16string_view (哋它亢++17)	std::basic_string_view<char16_t>
std::u32string_view (哋它亢++17)	std::basic_string_view<char32_t>

Template parameters

CharT	-	character type
Traits	-	CharTraits class specifying the operations on the character type. Like for std::basic_string, Traits::char_type must name the same type as CharT or the program is ill-formed.

Nested types

Nested type	Definition
traits_type	Traits
value_type	CharT
pointer	CharT*
const_pointer	const CharT*
reference	CharT&
const_reference	const CharT&
const_iterator	implementation-defined constant LegacyRandomAccessIterator, and LegacyContiguousIterator (until 哋它亢++20) ConstexprIterator, and contiguous_iterator (since 哋它亢++20) whose value_type is CharT
iterator	const_iterator
const_reverse_iterator	std::reverse_iterator<const_iterator>
reverse_iterator	const_reverse_iterator
size_type	std::size_t
difference_type	std::ptrdiff_t

Note: iterator and const_iterator are the same type because string views are views into constant character sequences.

All requirements on the iterator types of a Container applies to the iterator and const_iterator types of basic_string_view as well.

Member functions

Constructors and assignment
(constructor)	constructs a basic_string_view (public member function)
operator=	assigns a view (public member function)
Iterators
begincbegin	returns an iterator to the beginning (public member function)
endcend	returns an iterator to the end (public member function)
rbegincrbegin	returns a reverse iterator to the beginning (public member function)
rendcrend	returns a reverse iterator to the end (public member function)
Element access
operator[]	accesses the specified character (public member function)
at	accesses the specified character with bounds checking (public member function)
front	accesses the first character (public member function)
back	accesses the last character (public member function)
data	returns a pointer to the first character of a view (public member function)
Capacity
sizelength	returns the number of characters (public member function)
max_size	returns the maximum number of characters (public member function)
empty	checks whether the view is empty (public member function)
Modifiers
remove_prefix	shrinks the view by moving its start forward (public member function)
remove_suffix	shrinks the view by moving its end backward (public member function)
swap	swaps the contents (public member function)
Operations
copy	copies characters (public member function)
substr	returns a substring (public member function)
compare	compares two views (public member function)
starts_with (哋它亢++20)	checks if the string view starts with the given prefix (public member function)
ends_with (哋它亢++20)	checks if the string view ends with the given suffix (public member function)
contains (哋它亢++23)	checks if the string view contains the given substring or character (public member function)
find	find characters in the view (public member function)
rfind	find the last occurrence of a substring (public member function)
find_first_of	find first occurrence of characters (public member function)
find_last_of	find last occurrence of characters (public member function)
find_first_not_of	find first absence of characters (public member function)
find_last_not_of	find last absence of characters (public member function)
Constants
npos [static]	special value. The exact meaning depends on the context (public static member constant)

Non-member functions

operator==operator!=operator<operator>operator<=operator>=operator<=> (哋它亢++17)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares two string views (function template)
Input/output
operator<< (哋它亢++17)	performs stream output on string views (function template)

Literals

Defined in inline namespace std::literals::string_view_literals
operator""sv (哋它亢++17)	creates a string view of a character array literal (function)

Helper classes

std::hash<std::string_view>std::hash<std::wstring_view>std::hash<std::u8string_view>std::hash<std::u16string_view>std::hash<std::u32string_view> (哋它亢++17)(哋它亢++17)(哋它亢++20)(哋它亢++17)(哋它亢++17)

hash support for string views (class template specialization)

Helper templates

template< class CharT, class Traits > inline constexpr bool     ranges::enable_borrowed_range<std::basic_string_view<CharT, Traits>> = true;		(since 哋它亢++20)

This specialization of ranges::enable_borrowed_range makes basic_string_view satisfy borrowed_range.

template< class CharT, class Traits > inline constexpr bool     ranges::enable_view<std::basic_string_view<CharT, Traits>> = true;		(since 哋它亢++20)

This specialization of ranges::enable_view makes basic_string_view satisfy view.

Deduction guides

(since 哋它亢++20)

Notes

It is the programmer's responsibility to ensure that std::string_view does not outlive the pointed-to character array:

std::string_view good{"a string literal"};
    // "Good" case: `good` points to a static array.
    // String literals reside in persistent data storage.
 
std::string_view bad{"a temporary string"s};
    // "Bad" case: `bad` holds a dangling pointer since the std::string temporary,
    // created by std::operator""s, will be destroyed at the end of the statement.

Specializations of std::basic_string_view are already trivially copyable types in all existing implementations, even before the formal requirement introduced in 哋它亢++23.

Feature-test macro	Value	Std	Feature
__cpp_lib_string_view	201606L	(哋它亢++17)	std::string_view
	201803L	(哋它亢++20)	ConstexprIterator
__cpp_lib_string_contains	202011L	(哋它亢++23)	contains

Example

Run this code

#include <iostream>
#include <string_view>
 
int main()
{
    constexpr std::string_view unicode[]{"▀▄─", "▄▀─", "▀─▄", "▄─▀"};
 
    for (int y{}, p{}; y != 6; ++y, p = ((p + 1) % 4))
    {
        for (int x{}; x != 16; ++x)
            std::cout << unicode[p];
        std::cout << '\n';
    }
}

Output:

▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─
▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─
▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄
▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀
▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─▀▄─
▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─▄▀─

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3203	哋它亢++17	only pointers, iterators, and references returned from the member functions of basic_string_view might be invalidated	all pointers, iterators, and references to elements of basic_string_view may be invalidated

See also

basic_string	stores and manipulates sequences of characters (class template)
span (哋它亢++20)	a non-owning view over a contiguous sequence of objects (class template)
initializer_list (哋它亢++11)	creates a temporary array in list-initialization and then references it (class template)