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std::error_condition(3)	      C++ Standard Libary      std::error_condition(3)

NAME
       std::error_condition - std::error_condition

Synopsis
	  Defined in header <system_error>
	  class	error_condition;	    (since C++11)

	  std::error_condition	holds a	platform-independent value identifying
       an error
	  condition. Like std::error_code, it is uniquely identified by	an in-
       teger value and a
	  std::error_category, but unlike std::error_code, the value is	not
	  platform-dependent.

	  A typical implementation holds one integer data member  (the	value)
       and a pointer to
	  an std::error_category.

Member functions
	  constructor	constructs an error_condition
			(public	member function)
	  operator=	replaces the contents
			(public	member function)
	  assign	replaces the contents
			(public	member function)
	  clear		 sets  the error_condition to value 0 in generic_cate-
       gory
			(public	member function)
	  value		obtains	the value of the error_condition
			(public	member function)
	  category	obtains	the error_category for this error_condition
			(public	member function)
	  message	obtains	the explanatory	string
			(public	member function)
	  operator bool	checks if the value is non-zero
			(public	member function)

Non-member functions
	  operator==
	  operator!=
	  operator<	     compares error_conditions and error_codes
	  operator<=>	     (function)
	  (removed in C++20)
	  (removed in C++20)
	  (C++20)

Helper classes
	  is_error_condition_enum	   identifies  an  enumeration	as  an
       std::error_condition
	  (C++11)			  (class template)
	  std::hash<std::error_condition>  hash	 support for std::error_condi-
       tion
	  (C++17)			  (class template specialization)

Notes
	  The comparison between a std::error_code and a  std::error_condition
       is defined by
	  their	  error	  categories.	Notably,   an	error	condition   of
       std::generic_category may
	  compare equal	 to  an	 error	code  of  a  specific  category	 (e.g.
       std::system_category),
	  if they represent the	same kind of error.

	  A std::errc value can	be compared to an error	code via implicit con-
       version to
	  std::error_condition.

       // Run this code

	#include <cerrno>
	#include <iostream>
	#include <system_error>
	#include <Windows.h>

	int main()
	{
	    std::error_code ec{ERROR_FILE_EXISTS, std::system_category()};
	    std::error_condition econd{EEXIST, std::generic_category()};

	    std::cout.setf(std::ios::boolalpha);
	    std::cout << (ec ==	econd) << '\n';	// typically true
	    std::cout << (ec ==	std::errc::file_exists)	<< '\n'; // ditto
	    std::cout  <<  (ec	== make_error_code(std::errc::file_exists)) <<
       '\n'; //	false:
									     //
       different category
	}

Possible output:
	true
	true
	false

See also
	  error_code			   holds  a  platform-dependent	 error
       code
	  (C++11)			  (class)
	  error_category		  base class for error categories
	  (C++11)			  (class)
	  make_error_condition(std::errc)  creates  an	error condition	for an
       errc value e
	  (C++11)			  (function)

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

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