std::basic_string_view

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 C++23)

Several typedefs for common character types are provided:

Defined in header <string_view>

Type Definition

std::string_view (C++17) std::basic_string_view<char>

std::wstring_view (C++17) std::basic_string_view<wchar_t>

std::u8string_view (C++20) std::basic_string_view<char8_t>

std::u16string_view (C++17) std::basic_string_view<char16_t>

std::u32string_view (C++17) std::basic_string_view<char32_t>

[edit] 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.

[edit] Nested types

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 C++20)

ConstexprIterator, and contiguous_iterator (since C++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.

[edit] Data members

Member Description

const_pointer data_ a pointer to the underlying sequence
(exposition-only member object*)

size_type size_ the number of characters
(exposition-only member object*)

[edit] Member functions

Constructors and assignment

(constructor)

constructs a basic_string_view
(public member function) [edit]

operator=

assigns a view
(public member function) [edit]

Iterators

begincbegin

returns an iterator to the beginning
(public member function) [edit]

endcend

returns an iterator to the end
(public member function) [edit]

rbegincrbegin

returns a reverse iterator to the beginning
(public member function) [edit]

rendcrend

returns a reverse iterator to the end
(public member function) [edit]

Element access

operator[]

accesses the specified character
(public member function) [edit]

at

accesses the specified character with bounds checking
(public member function) [edit]

front

accesses the first character
(public member function) [edit]

back

accesses the last character
(public member function) [edit]

data

returns a pointer to the first character of a view
(public member function) [edit]

Capacity

sizelength

returns the number of characters
(public member function) [edit]

max_size

returns the maximum number of characters
(public member function) [edit]

empty

checks whether the view is empty
(public member function) [edit]

Modifiers

remove_prefix

shrinks the view by moving its start forward
(public member function) [edit]

remove_suffix

shrinks the view by moving its end backward
(public member function) [edit]

swap

swaps the contents
(public member function) [edit]

Operations

copy

copies characters
(public member function) [edit]

substr

returns a substring
(public member function) [edit]

compare

compares two views
(public member function) [edit]

starts_with

(C++20)

checks if the string view starts with the given prefix
(public member function) [edit]

ends_with

(C++20)

checks if the string view ends with the given suffix
(public member function) [edit]

contains

(C++23)

checks if the string view contains the given substring or character
(public member function) [edit]

find

find characters in the view
(public member function) [edit]

rfind

find the last occurrence of a substring
(public member function) [edit]

find_first_of

find first occurrence of characters
(public member function) [edit]

find_last_of

find last occurrence of characters
(public member function) [edit]

find_first_not_of

find first absence of characters
(public member function) [edit]

find_last_not_of

find last absence of characters
(public member function) [edit]

Constants

npos

[static]

special value. The exact meaning depends on the context
(public static member constant) [edit]

[edit] Non-member functions

operator==operator!=operator<operator>operator<=operator>=operator<=>

(C++17)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)

lexicographically compares two string views
(function template) [edit]

Input/output

operator<<

(C++17)

performs stream output on string views
(function template) [edit]

[edit] Literals

Defined in inline namespace std::literals::string_view_literals

operator""sv

(C++17)

creates a string view of a character array literal
(function) [edit]

[edit] 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>

(C++17)(C++17)(C++20)(C++17)(C++17)

hash support for string views
(class template specialization) [edit]

[edit] Helper templates

template< class CharT, class Traits >

inline constexpr bool

ranges::enable_borrowed_range <std::basic_string_view<CharT, Traits>> = true;

(since C++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 C++20)

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

Deduction guides

(since C++20)

[edit] 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 C++23.

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

[edit] Example

Run this code

#include <iostream>
#include <string_view>
 
int main()
{
 #define A "▀"
 #define B "▄"
 #define C "─"
 
 constexpr std::string_view blocks[]{A B C, B A C, A C B, B C A};
 
 for (int y{}, p{}; y != 8; ++y, p = ((p + 1) % 4))
 {
 for (char x{}; x != 29; ++x)
 std::cout << blocks[p];
 std::cout << '\n';
 }
}

Output:

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

[edit] Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 3203	C++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

[edit] See also

basic_string

stores and manipulates sequences of characters
(class template) [edit]

operator+

concatenates two strings, a string and a char, or a string and string_view
(function template) [edit]

span

(C++20)

a non-owning view over a contiguous sequence of objects
(class template) [edit]

initializer_list

(C++11)

references a temporary array created in list-initialization
(class template) [edit]

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std::basic_string_view

Contents

[edit] Template parameters

[edit] Nested types

[edit] Data members

[edit] Member functions

Constructors and assignment

Iterators

Element access

Capacity

Modifiers

Operations

Constants

[edit] Non-member functions

Input/output

[edit] Literals

[edit] Helper classes

[edit] Helper templates

Deduction guides

[edit] Notes

[edit] Example

[edit] Defect reports

[edit] See also

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