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

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< cpp‎ | string‎ | basic string
m (→‎Notes: + feature test macro; fmt)
m (Minor fix.)
 
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{{cpp/title|n=literals::string_literals::|operator""s }}
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{{cpp/title|n=literals::string_literals::|operator""s}}
 
{{cpp/string/basic_string/navbar}}
 
{{cpp/string/basic_string/navbar}}
 
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{{|num=1|=c++14|=c++20|
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| since1=c++14 | dcl1=
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std::string operator""s( const char* str, std::size_t len );
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std::string operator""s(const char *str, std::size_t len);
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| since2=c++20 | dcl2=
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constexpr std::string operator""s(const char *str, std::size_t len);
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}}
 
}}
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{{dcl|num=2|since=c++20|
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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,
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std::size_t len );
 
}}
 
}}
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{{|num=3|=c++14|=c++20|
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std::u16string operator""s( const char16_t* str, std::size_t len );
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std::u16string operator""s(const char16_t *str, std::size_t len);
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constexpr std::u16string operator""s(const char16_t *str, std::size_t len);
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std::u32string operator""s( const char32_t* str, std::size_t len );
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std::u32string operator""s(const char32_t *str, std::size_t len);
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constexpr std::u32string operator""s(const char32_t *str, std::size_t len);
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std::wstring operator""s( const wchar_t* str, std::size_t len );
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std::wstring operator""s(const wchar_t *str, std::size_t len);
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constexpr std::wstring operator""s(const wchar_t *str, std::size_t len);
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Forms a string literal of the desired type.
 
Forms a string literal of the desired type.
  
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@1@ returns {{c|std::string{str, len} }}
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@1@ {{c|std::string{str, len} }}
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@2@ returns {{c|std::u8string{str, len} }}
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@2@ {{c|std::u8string{str, len} }}
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@3@ returns {{c|std::u16string{str, len} }}
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@3@ {{c|std::u16string{str, len} }}
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@4@ returns {{c|std::u32string{str, len} }}
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@4@ {{c|std::u32string{str, len} }}
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@5@ returns {{c|std::wstring{str, len} }}
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@5@ {{c|std::wstring{str, len} }}
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
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{{par | str | pointer to the beginning of the raw character array literal}}
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{{par|str|pointer to the beginning of the raw character array literal}}
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{{par | len | length of the raw character array literal}}
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{{par|len|length of the raw character array literal}}
 
{{par end}}
 
{{par end}}
  
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===Notes===
 
===Notes===
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These operators are declared in the namespace {{c|std::literals::string_literals}}, where both {{tt|literals}} and {{tt|string_literals}} are inline namespaces. Access to these operators can be gained with either <br>
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These operators are declared in the namespace {{c|std::literals::string_literals}}, where both {{tt|literals}} and {{tt|string_literals}} are inline namespaces. Access to these operators can be gained with
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* {{c|using namespace std::literals}}, or
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* {{c|using namespace std::literals}}
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* {{c|using namespace std::string_literals}}, or
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* {{c|using namespace std::string_literals}}
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* {{c|using namespace std::literals::string_literals}}.
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* {{c|using namespace std::literals::string_literals}}
  
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{{lc|std::chrono::duration}} also defines {{c|operator""s}}, to represent literal seconds, but it is an arithmetic literal: {{c|10.0s}} and {{c|10s}} are ten seconds, but {{c|"10"s}} is a string.
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{{lc|std::chrono::duration}} also defines {{|operator""s}} to represent literal seconds, but it is an arithmetic literal: {{c|10.0s}} and {{c|10s}} are ten seconds, but {{c|"10"s}} is a string.
  
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{{feature test macro|__cpp_lib_string_udls}}
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{{feature test macro|__cpp_lib_string_udls}}
  
 
===Example===
 
===Example===
 
{{example
 
{{example
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| code=
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|code=
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#include <string>
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#include <iostream>
 
#include <iostream>
 +
 +
 +
 +
 +
 +
 +
 +
 +
  
 
int main()
 
int main()
 
{
 
{
 
     using namespace std::string_literals;
 
     using namespace std::string_literals;
−
 
+
 
     std::string s1 = "abc\0\0def";
 
     std::string s1 = "abc\0\0def";
 
     std::string s2 = "abc\0\0def"s;
 
     std::string s2 = "abc\0\0def"s;
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     std::cout << "s1: " << s1.size() << ' ' << s1 << '\n'
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     "s1: "s1)
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              << "s2: " << s2.size() << ' ' << s2 << '\n'
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"s2: "s2)
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              << "abcdef"s.substr(1,4) << '\n';
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 +
<< "abcdef"s.substr(1,4) << '\n';
 
}
 
}
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| p=true
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|output=
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| output=  
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s1: 3
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s1: 3 abc
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s2: 8
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s2: 8 abc^@^@def
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bcde
 
bcde
 
}}
 
}}
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===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{dsc inc | cpp/string/basic_string/dsc constructor}}
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{{dsc inc|cpp/string/basic_string/dsc constructor}}
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{{dsc inc | cpp/string/basic_string_view/dsc operator""sv}}
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{{dsc inc|cpp/string/basic_string_view/dsc operator""sv}}
 
{{dsc end}}
 
{{dsc end}}
  
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 18:47, 16 December 2024

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

[edit] Parameters

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

[edit] Return value

The string literal.

[edit] 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 any of the following using directives:

  • using namespace std::literals
  • using namespace std::string_literals
  • 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

[edit] Example

Run this code
#include <iostream>
#include <string>
 
void print_with_zeros(const auto note, const std::string& 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

[edit] 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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