std::system_category (3) - Linux Manuals

std::system_category: std::system_category


std::system_category - std::system_category


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 reported by the operating system. The object is required to override the virtual function 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.



Return value

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


// Run this code

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

  int main()
      std::error_condition econd = std::system_category().default_error_condition(EDOM);
      std::cout << "Category: " << econd.category().name() << '\n'
                << "Value: " << econd.value() << '\n'
                << "Message: " << econd.message() << '\n';

      econd = std::system_category().default_error_condition(10001);
      std::cout << "Category: " << econd.category().name() << '\n'
                << "Value: " << econd.value() << '\n'
                << "Message: " << econd.message() << '\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

errc the std::error_condition enumeration listing all standard <cerrno> macro constants