W3cubDocs

/C++

std::basic_string_view

Defined in header `<string_view>`
template< class CharT, class Traits = std::char_traits<CharT> > class basic_string_view;		(since C++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.

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

(since C++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` (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>

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.

Member types

Member 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.

Member functions

Constructors and assignment
(constructor) (C++17)	constructs a `basic_string_view` (public member function)
operator= (C++17)	assigns a view (public member function)
Iterators
begincbegin (C++17)	returns an iterator to the beginning (public member function)
endcend (C++17)	returns an iterator to the end (public member function)
rbegincrbegin (C++17)	returns a reverse iterator to the beginning (public member function)
rendcrend (C++17)	returns a reverse iterator to the end (public member function)
Element access
operator[] (C++17)	accesses the specified character (public member function)
at (C++17)	accesses the specified character with bounds checking (public member function)
front (C++17)	accesses the first character (public member function)
back (C++17)	accesses the last character (public member function)
data (C++17)	returns a pointer to the first character of a view (public member function)
Capacity
sizelength (C++17)	returns the number of characters (public member function)
max_size (C++17)	returns the maximum number of characters (public member function)
empty (C++17)	checks whether the view is empty (public member function)
Modifiers
remove_prefix (C++17)	shrinks the view by moving its start forward (public member function)
remove_suffix (C++17)	shrinks the view by moving its end backward (public member function)
swap (C++17)	swaps the contents (public member function)
Operations
copy (C++17)	copies characters (public member function)
substr (C++17)	returns a substring (public member function)
compare (C++17)	compares two views (public member function)
starts_with (C++20)	checks if the string view starts with the given prefix (public member function)
ends_with (C++20)	checks if the string view ends with the given suffix (public member function)
contains (C++23)	checks if the string view contains the given substring or character (public member function)
find (C++17)	find characters in the view (public member function)
rfind (C++17)	find the last occurrence of a substring (public member function)
find_first_of (C++17)	find first occurrence of characters (public member function)
find_last_of (C++17)	find last occurrence of characters (public member function)
find_first_not_of (C++17)	find first absence of characters (public member function)
find_last_not_of (C++17)	find last absence of characters (public member function)
Constants
npos [static] (C++17)	special value. The exact meaning depends on the context (public static member constant)

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)
Input/output
operator<< (C++17)	performs stream output on string views (function template)

Literals

Defined in inline namespace `std::literals::string_view_literals`
operator""sv (C++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>

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

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	Comment
`__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`

Example

#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:

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

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

std::basic_string_view

Template parameters

Member types

Member functions

Constructors and assignment

Iterators

Element access

Capacity

Modifiers

Operations

Constants