std::system_error::system_error(3)

NAME
std::system_error::system_error - std::system_error::system_error

Synopsis
   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, (4) (since C++11)
   const std::string& what_arg );
   system_error( int ev, const std::error_category& ecat, (4) (since C++11)
   const char* what_arg );
   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(), "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