Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::from_chars_result(3)     C++ Standard Libary    std::from_chars_result(3)

NAME
       std::from_chars_result -	std::from_chars_result

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

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

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

Example
       // Run this code

	#include <cassert>
	#include <charconv>
	#include <iomanip>
	#include <iostream>
	#include <optional>
	#include <string_view>
	#include <system_error>

	int main()
	{
	    for	(std::string_view const	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';
		else if	(ec == std::errc::invalid_argument)
		    std::cout << "This is not a	number.\n";
		else if	(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 >= 202306L
		if (std::from_chars(s.data(), s.data() + s.size(), value))
	#else
		if  (std::from_chars(s.data(),	s.data() + s.size(), value).ec
       == std::errc{})
	#endif
		    return value;
		else
		    return std::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.

See also
	  from_chars converts a	character sequence to an integer or  floating-
       point value
	  (C++17)    (function)

http://cppreference.com		  2024.06.10	     std::from_chars_result(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::from_chars_result&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>

home | help