std::iostream_category(3)

NAME
std::iostream_category - std::iostream_category

Synopsis
   Defined in header <ios>
   const std::error_category& iostream_category() noexcept; (since C++11)
   Obtains a reference to the static error category object for iostream errors. The
   object is required to override the virtual function error_category::name() to return
   a pointer to the string "iostream". It is used to identify error codes provided in
   the exceptions of type std::ios_base::failure.

Parameters
   (none)

Return value
   A reference to the static object of unspecified runtime type, derived from
   std::error_category.

Example
// Run this code
 #include <fstream>
 #include <iostream>
 int main()
 {
     std::ifstream f("doesn't exist");
     try
     {
         f.exceptions(f.failbit);
     }
     catch (const std::ios_base::failure& e)
     {
         std::cout << "Caught an ios_base::failure.\n"
                   << "Error code: " << e.code().value()
                   << " (" << e.code().message() << ")\n"
                   << "Error category: " << e.code().category().name() << '\n';
     }
 }

Possible output:
 Caught an ios_base::failure.
 Error code: 1 (unspecified iostream_category error)
 Error category: iostream
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 2087 C++11 iostream_category was not declared noexcept declared noexcept

See also
   failure stream exception
           (public member class of std::ios_base)
   io_errc the IO stream error codes
   (C++11) (enum)