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Defined in header <charconv> | ||
struct from_chars_result; | (since C++17) | |
std::from_chars_result is the return type ofstd::from_chars. It has no base classes, and only has the following members.
Contents |
| Member name | Definition |
ptr | a pointer of typeconstchar* (public member object) |
ec | an error code of typestd::errc (public member object) |
friendbool operator==(const from_chars_result&, const from_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::from_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 <cassert>#include <charconv>#include <iomanip>#include <iostream>#include <optional>#include <string_view>#include <system_error> int main(){for(std::string_viewconst str:{"1234","15 foo","bar"," 42","5000000000"}){std::cout<<"String: "<<std::quoted(str)<<". ";int result{};auto[ptr, ec]=std::from_chars(str.data(), str.data()+ str.size(), result); if(ec==std::errc())std::cout<<"Result: "<< result<<", ptr -> "<<std::quoted(ptr)<<'\n';elseif(ec==std::errc::invalid_argument)std::cout<<"This is not a number.\n";elseif(ec==std::errc::result_out_of_range)std::cout<<"This number is larger than an int.\n";} // C++23's constexpr from_char demo / C++26's operator bool() demo:auto to_int=[](std::string_view s)->std::optional<int>{int value{};#if __cpp_lib_to_chars >= 202306Lif(std::from_chars(s.data(), s.data()+ s.size(), value))#elseif(std::from_chars(s.data(), s.data()+ s.size(), value).ec==std::errc{})#endifreturn value;elsereturnstd::nullopt;}; assert(to_int("42")==42);assert(to_int("foo")==std::nullopt);#if __cpp_lib_constexpr_charconv and __cpp_lib_optional >= 202106 static_assert(to_int("42")==42); static_assert(to_int("foo")==std::nullopt);#endif}
Output:
String: "1234". Result: 1234, ptr -> ""String: "15 foo". Result: 15, ptr -> " foo"String: "bar". This is not a number.String: " 42". This is not a number.String: "5000000000". This number is larger than an int.
(C++17) | converts a character sequence to an integer or floating-point value (function)[edit] |
