std:: basic_string_view

From cppreference.com
C++
Strings library
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)

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

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.

Member functions

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

Constants

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

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

Literals

Defined in inline namespace std::literals::string_view_literals
(C++17)
creates a string view of a character array literal
(function)

Helper classes

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

See also

stores and manipulates sequences of characters
(class template)
concatenates two strings, a string and a char , or a string and string_view
(function template)
(C++20)
a non-owning view over a contiguous sequence of objects
(class template)
(C++11)
references a temporary array created in list-initialization
(class template)
Retrieved from " https://en.cppreference.com/mwiki/index.php?title=cpp/string/basic_string_view&oldid=173499 "