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

NAME
     std::system_category - std::system_category

Synopsis
	Defined in header <system_error>
	const std::error_category& system_category() noexcept;	(since C++11)

	Obtains  a  reference to the static error category object for errors re-
     ported by the
	operating system. The object is required to override the  virtual  func-
     tion
	std::error_category::name()  to return a pointer to the string "system".
     It is also
	required to override the virtual function
	std::error_category::default_error_condition() to map  the  error  codes
     that match
	POSIX errno values to std::generic_category.

Parameters
	(none)

Return value
	A  reference  to  the static object of unspecified runtime type, derived
     from
	std::error_category.

Notes
	On Windows, system_category() typically maps some Windows error codes to
     POSIX ones.
	On POSIX, system_category() tends to be equivalent to std::generic_cate-
     gory() except
	for the name.

Example
     // Run this code

      #include <iomanip>
      #include <iostream>
      #include <string>
      #include <system_error>

      int main()
      {
	  for (int const code : {EDOM, 10001})
	  {
	      const std::error_condition econd =
		  std::system_category().default_error_condition(code);

	      std::cout << "Category: " << econd.category().name() << '\n'
			<< "Value:    " << econd.value() << '\n'
			<< "Message:  " << econd.message() << "\n\n";
	  }
      }

Possible output:
      Category: generic
      Value:	33
      Message:	Numerical argument out of domain

      Category: system
      Value:	10001
      Message:	Unknown error 10001

See also
	generic_category identifies the generic error category
	(C++11) 	 (function)
	errc		 the std::error_condition enumeration listing all  stan-
     dard <cerrno>
	(C++11) 	 macro constants
			 (class)

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