# std::system_category

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< cpp‎ | error

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

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