Namespaces
Variants
Views
Actions

std::basic_string_view

From cppreference.com
< cpp‎ | string
 
 
 
 
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)

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>

Contents

[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

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 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] Member functions

Constructors and assignment
constructs a basic_string_view
(public member function) [edit]
assigns a view
(public member function) [edit]
Iterators
returns an iterator to the beginning
(public member function) [edit]
returns an iterator to the end
(public member function) [edit]
returns a reverse iterator to the beginning
(public member function) [edit]
returns a reverse iterator to the end
(public member function) [edit]
Element access
accesses the specified character
(public member function) [edit]
accesses the specified character with bounds checking
(public member function) [edit]
accesses the first character
(public member function) [edit]
accesses the last character
(public member function) [edit]
returns a pointer to the first character of a view
(public member function) [edit]
Capacity
returns the number of characters
(public member function) [edit]
returns the maximum number of characters
(public member function) [edit]
checks whether the view is empty
(public member function) [edit]
Modifiers
shrinks the view by moving its start forward
(public member function) [edit]
shrinks the view by moving its end backward
(public member function) [edit]
swaps the contents
(public member function) [edit]
Operations
copies characters
(public member function) [edit]
returns a substring
(public member function) [edit]
compares two views
(public member function) [edit]
checks if the string view starts with the given prefix
(public member function) [edit]
(C++20)
checks if the string view ends with the given suffix
(public member function) [edit]
(C++23)
checks if the string view contains the given substring or character
(public member function) [edit]
find characters in the view
(public member function) [edit]
find the last occurrence of a substring
(public member function) [edit]
find first occurrence of characters
(public member function) [edit]
find last occurrence of characters
(public member function) [edit]
find first absence of characters
(public member function) [edit]
find last absence of characters
(public member function) [edit]

Constants

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

[edit] Non-member functions

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

[edit] Literals

Defined in inline namespace std::literals::string_view_literals
creates a string view of a character array literal
(function) [edit]

[edit] Helper classes

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
201803L (C++20) ConstexprIterator
__cpp_lib_string_contains 202011L (C++23) contains

[edit] 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:

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

[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

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