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Difference between revisions of "cpp/string/basic string/operator""s"

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< cpp‎ | string‎ | basic string
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constexpr std::u8string operator""s( const char8_t *str, std::size_t len );
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constexpr std::u8string operator""s( const char8_t* str, std::size_t len );
 
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Revision as of 23:34, 21 October 2023

 
C++
 
Strings library
 
std::basic_string
 
Defined in header <string>
(1)
std::string operator""s( const char* str, std::size_t len );
 (since C++14)
(until C++20)
constexpr std::string operator""s( const char* str, std::size_t len );
 (since C++20)
constexpr std::u8string operator""s( const char8_t* str, std::size_t len );
 (2) (since C++20)
(3)
std::u16string operator""s( const char16_t* str, std::size_t len );
 (since C++14)
(until C++20)
constexpr std::u16string operator""s( const char16_t* str, std::size_t len );
 (since C++20)
(4)
std::u32string operator""s( const char32_t* str, std::size_t len );
 (since C++14)
(until C++20)
constexpr std::u32string operator""s( const char32_t* str, std::size_t len );
 (since C++20)
(5)
std::wstring operator""s( const wchar_t* str, std::size_t len );
 (since C++14)
(until C++20)
constexpr std::wstring operator""s( const wchar_t* str, std::size_t len );
 (since C++20)

Forms a string literal of the desired type.

1) Returns std::string{str, len}.
2) Returns std::u8string{str, len}.
3) Returns std::u16string{str, len}.
4) Returns std::u32string{str, len}.
5) Returns std::wstring{str, len}.

Contents

Parameters

str - pointer to the beginning of the raw character array literal
len - length of the raw character array literal

Return value

The string literal.

Notes

These operators are declared in the namespace std::literals::string_literals, where both literals and string_literals are inline namespaces. Access to these operators can be gained with either

  • using namespace std::literals, or
  • using namespace std::string_literals, or
  • using namespace std::literals::string_literals.

std::chrono::duration also defines operator""s, to represent literal seconds, but it is an arithmetic literal: 10.0s and 10s are ten seconds, but "10"s is a string.

Feature-test macro Value Std Feature
__cpp_lib_string_udls 201304L (C++14) User-defined literals for string types

Example

Run this code
#include <iostream>
#include <string>
 
void print_with_zeros(auto const note, std::string const& s)
{
    std::cout << note;
    for (const char c : s)
        c ? std::cout << c : std::cout << "₀";
    std::cout << " (size = " << s.size() << ")\n";
}
 
int main()
{
    using namespace std::string_literals;
 
    std::string s1 = "abc\0\0def";
    std::string s2 = "abc\0\0def"s;
    print_with_zeros("s1: ", s1);
    print_with_zeros("s2: ", s2);
 
    std::cout << "abcdef"s.substr(1,4) << '\n';
}

Output: 

s1: abc (size = 3)
s2: abc₀₀def (size = 8)
bcde

See also

 constructs a basic_string
(public member function) [edit]
(C++17)
 creates a string view of a character array literal
(function) [edit]
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