std::from_chars_result(3) - FreeBSD Ports 15.1.quarterly Manual Pages

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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)
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