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.

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>

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

Type Definition

traits_type Traits

value_type CharT

pointer CharT*

const_pointer constCharT*

reference CharT&

const_reference constCharT&

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.

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*)

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)
subview (C++26)	returns a sub-view (public member function)
compare	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	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<=> (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	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`

Example

#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:

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

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

basic_string	stores and manipulates sequences of characters (class template)
operator+	concatenates two strings, a string and a char, or a string and `string_view` (function template)
span (C++20)	a non-owning view over a contiguous sequence of objects (class template)
initializer_list (C++11)	references a temporary array created in list-initialization (class template)

std::basic_string_view

Template parameters

Nested types

Data members

Member functions

Constructors and assignment

Iterators

Element access

Capacity

Modifiers

Operations

Constants

Non-member functions

Input/output

Literals

Helper classes

Helper templates

Deduction guides

Notes

Example

Defect reports

See also