std::to_chars_result

 

C++

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Primitive numeric conversions

to_chars (C++17) to_chars_result (C++17) from_chars (C++17) from_chars_result (C++17) chars_format (C++17)

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text_encoding (C++26)

 

Defined in header <charconv>
struct to_chars_result;		(since C++17)

std::to_chars_result is the return type of std::to_chars. It has no base classes, and only has the following members.

Data members

Member name	Definition
ptr	a pointer of type char* (public member object)
ec	an error code of type std::errc (public member object)

Member and friend functions

operator==(std::to_chars_result)

friendbool operator==(const to_chars_result&,                         const to_chars_result&)=default;		(since C++20)

Compares the two arguments using default comparisons (which uses operator== to compare ptr and ec respectively).

This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::to_chars_result is an associated class of the arguments.

The != operator is synthesized from operator==.

operator bool

constexprexplicit operator bool()constnoexcept;		(since C++26)

Checks whether the conversion is successful. Returns ec ==std::errc{}.

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_to_chars	201611L	(C++17)	Elementary string conversions (std::to_chars, std::from_chars)
	202306L	(C++26)	Testing for success or failure of <charconv> functions

Example

Run this code

#include <array>#include <charconv>#include <iostream>#include <string_view>#include <system_error>   void show_to_chars(auto... format_args){std::array<char, 10> str;   #if __cpp_lib_to_chars >= 202306L and __cpp_structured_bindings >= 202406L// use C++26 structured bindings declaration as condition (P0963)// and C++26 to_chars_result::operator bool() for error checking (P2497)if(auto[ptr, ec]=std::to_chars(str.data(), str.data()+ str.size(), format_args...))std::cout<<std::string_view(str.data(), ptr)<<'\n';elsestd::cout<<std::make_error_code(ec).message()<<'\n';#elif __cpp_lib_to_chars >= 202306L// use C++26 to_chars_result::operator bool() for error checking (P2497)if(auto result =std::to_chars(str.data(), str.data()+ str.size(), format_args...))std::cout<<std::string_view(str.data(), result.ptr)<<'\n';elsestd::cout<<std::make_error_code(result.ec).message()<<'\n';#else// fallback to C++17 if-with-initializer and structured bindingsif(auto[ptr, ec]=std::to_chars(str.data(), str.data()+ str.size(), format_args...); ec ==std::errc())std::cout<<std::string_view(str.data(), ptr - str.data())<<'\n';elsestd::cout<<std::make_error_code(ec).message()<<'\n';#endif}   int main(){ show_to_chars(42); show_to_chars(+3.14159F); show_to_chars(-3.14159, std::chars_format::fixed); show_to_chars(-3.14159, std::chars_format::scientific, 3); show_to_chars(3.1415926535, std::chars_format::fixed, 10);}

Possible output:

42 3.14159 -3.14159 -3.142e+00 Value too large for defined data type

See also

to_chars (C++17)

converts an integer or floating-point value to a character sequence (function)