# 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)
system_error( const system_error& other ) noexcept; | (5) | (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 (assuming that it doesn't contain an embedded null character).
5) Copy constructor. Initializes the contents with those of other. If *this and other both have dynamic type `std::system_error` then std::strcmp (what(), other.what()) == 0.

### Parameters

ec | - | error code
ev | - | underlying error code in the enumeration associated with ecat
ecat | - | the category of error
what_arg | - | explanatory string
other | - | another `system_error` to copy

### 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(), "FIX ME");
        }
        catch (const std::system_error& ex)
        {
            std::cout << "code:    [" << ex.code() << "]\n"
                         "message: [" << ex.code().message() << "]\n"
                         "what:    [" << ex.what() << "]\n";
        }
    }

Possible output:

    code:    [generic:33]
    message: [Numerical argument out of domain]
    what:    [FIX ME: Numerical argument out of domain]

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