std::system_error:: system_error

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
Diagnostics library
std::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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