std::system_category

 

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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 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) Stacktrace stacktrace_entry (C++23) basic_stacktrace (C++23) Debugging support is_debugger_present (C++26) breakpoint_if_debugging (C++26) breakpoint (C++26)

 

Defined in header <system_error>
conststd::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(intconst code :{EDOM, 10001}){conststd::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)