std::basic_string_view

 

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basic_string_view (C++17)

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std::basic_string_view

Member functions basic_string_view::basic_string_view    basic_string_view::operator= Iterators basic_string_view::beginbasic_string_view::cbegin basic_string_view::endbasic_string_view::cend basic_string_view::rbeginbasic_string_view::crbegin basic_string_view::rendbasic_string_view::crend Element access basic_string_view::at basic_string_view::operator[] basic_string_view::front basic_string_view::back basic_string_view::data Capacity basic_string_view::sizebasic_string_view::length basic_string_view::max_size basic_string_view::empty Modifiers basic_string_view::remove_prefix basic_string_view::remove_suffix basic_string_view::swap

Operations basic_string_view::copy basic_string_view::substr basic_string_view::compare basic_string_view::starts_with (C++20) basic_string_view::ends_with (C++20) basic_string_view::contains (C++23) basic_string_view::find basic_string_view::rfind basic_string_view::find_first_of basic_string_view::find_last_of basic_string_view::find_first_not_of basic_string_view::find_last_not_of Constants basic_string_view::npos Non-member functions operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) operator<< operator""sv Helper classes hash<std::string_view>hash<std::wstring_view>hash<std::u8string_view>hash<std::u16string_view>hash<std::u32string_view> (C++20) Deduction guides(C++20)

 

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.

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
	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:

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

See also

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)