# std::system_error::system_error

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< cpp‎ | error‎ | system error

system_error( std::error_code ec ); | (1) | (since C++11)
system_error( std::error_code ec, const std::string & what_arg ); | (2) | (since C++11)
system_error( std::error_code ec, const char* what_arg ); | (2) | (since C++11)
system_error( int ev, const std::error_category & ecat ); | (3) | (since C++11)
system_error( int ev, const std::error_category & ecat, const std::string & what_arg); | (4) | (since C++11)
system_error( int ev, const std::error_category & ecat, const char* what_arg); | (4) | (since C++11)

Constructs new system error object.

1) Constructs with error code `ec`
2) Constructs with error code `ec` and explanation string `what_arg`. The string returned by what() is guaranteed to contain `what_arg` as a substring.
3) Constructs with underlying error code `ev` and associated error category `ecat`.
4) Constructs with underlying error code `ev`, associated error category `ecat` and explanatory string `what_arg`. The string returned by what() is guaranteed to contain `what_arg` as a substring.

### Parameters

ec | - | error code
ev | - | underlying error code in the enumeration associated with `ecat`
ecat | - | the category of error
what_arg | - | explanatory string

### Example

Demonstrates how to create a system_error exception from an `errno` value.

Run this code

    #include <iostream>
    #include <system_error>

    int main()
    {
        try
        {
            throw std::system_error(EDOM, std::generic_category(), "hello world");
        }
        catch (const std::system_error& ex)
        {
            std::cout << ex.code() << '\n';
            std::cout << ex.code().message() << '\n';
            std::cout << ex.what() << '\n';
        }
    }

Possible output:

    generic:33
    Numerical argument out of domain
    hello world: Numerical argument out of domain

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