std::system_category

 

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Exception handling exception uncaught_exceptionuncaught_exceptions (until C++20*)(C++17) exception_ptr (C++11) make_exception_ptr (C++11) current_exception (C++11) rethrow_exception (C++11) nested_exception (C++11) throw_with_nested (C++11) rethrow_if_nested (C++11) Exception handling failures terminate terminate_handler get_terminate (C++11) set_terminate bad_exception unexpected (until C++17*) unexpected_handler (until C++17*) get_unexpected (C++11)(until C++17*)     set_unexpected (until C++17*) Error codes Error codes errno

Exception categories logic_error invalid_argument domain_error length_error out_of_range runtime_error range_error overflow_error underflow_error tx_exception (TM TS) System error support error_category (C++11) generic_category (C++11) system_category (C++11) error_condition (C++11) errc (C++11) error_code (C++11) system_error (C++11) Assertions assert Stacktrace stacktrace_entry (C++23) basic_stacktrace (C++23)

 

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.

Parameters

(none)

Return value

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

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 (C++11)	identifies the generic error category (function)
errc (C++11)	the std::error_condition enumeration listing all standard <cerrno> macro constants (class)