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 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.

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_category() 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 standard <cerrno>
(C++11) macro constants
(class)