| Localization library | |||||||||||||||||||||||||
| Regular expressions library(C++11) | |||||||||||||||||||||||||
| Formatting library(C++20) | |||||||||||||||||||||||||
| Null-terminated sequence utilities | |||||||||||||||||||||||||
| Byte strings | |||||||||||||||||||||||||
| Multibyte strings | |||||||||||||||||||||||||
| Wide strings | |||||||||||||||||||||||||
| Primitive numeric conversions | |||||||||||||||||||||||||
| |||||||||||||||||||||||||
| Text encoding identifications | |||||||||||||||||||||||||
| |||||||||||||||||||||||||
Defined in header <charconv> | ||
struct to_chars_result; | (since C++17) | |
std::to_chars_result is the return type ofstd::to_chars. It has no base classes, and only has the following members.
Contents |
| Member name | Definition |
ptr | a pointer of typechar* (public member object) |
ec | an error code of typestd::errc (public member object) |
friendbool operator==(const to_chars_result&, const to_chars_result&)=default; | (since C++20) | |
Compares the two arguments usingdefault comparisons (which usesoperator== to compareptr andec respectively).
This function is not visible to ordinaryunqualified orqualified lookup, and can only be found byargument-dependent lookup when std::to_chars_result is an associated class of the arguments.
The!= operator issynthesized fromoperator==.
constexprexplicit operatorbool()constnoexcept; | (since C++26) | |
Checks whether the conversion is successful. Returnsec==std::errc{}.
| 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 |
#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:
423.14159-3.14159-3.142e+00Value too large for defined data type
(C++17) | converts an integer or floating-point value to a character sequence (function)[edit] |
