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#include <iostream>
using namespace std;
#include <system_error>
#include <cassert>
 
namespace mylib
{
    namespace errc {
 
        enum my_error
        {
            failed = 0
        };
 
        inline const char* error_message(int c)
        {
            static const char* err_msg[] = 
            {
                "Failed",
            };
 
            assert(c < sizeof(err_msg) / sizeof(err_msg[0]));
            return err_msg[c];
        }
 
        class my_error_category : public std::error_category
        {
            public:
 
            my_error_category()
            { }
 
            std::string message(int c) const
            { 
                return error_message(c); 
            }
 
            const char* name() const { return "My Error Category"; }
 
            const static error_category& get()
            {
                const static my_error_category category_const;
                return category_const;
            }
        };
 
    } // end namespace errc
} // end namespace mylib
 
namespace std {
 
inline error_code make_error_code(mylib::errc::my_error e)
{
    return error_code(static_cast<int>(e), mylib::errc::my_error_category::get());
}
 
template<>
struct is_error_code_enum<mylib::errc::my_error>
    : std::true_type
{ }; 
 
} // end namespace std
 
int main()
{
    std::error_code ec1 = std::make_error_code(mylib::errc::failed); // works
    std::error_code ec2 = mylib::errc::failed; // doesn't compile
    bool result = (ec2 == mylib::errc::failed); // doesn't compile
}
 

In file included from prog.cpp:3:0:
/usr/lib/gcc/i686-pc-linux-gnu/4.5.1/../../../../include/c++/4.5.1/system_error: In constructor 'std::error_code::error_code(_ErrorCodeEnum, typename std::enable_if<std::is_error_code_enum<_ErrorCodeEnum>::value>::type*) [with _ErrorCodeEnum = mylib::errc::my_error, typename std::enable_if<std::is_error_code_enum<_ErrorCodeEnum>::value>::type = void]':
prog.cpp:67:40:   instantiated from here
/usr/lib/gcc/i686-pc-linux-gnu/4.5.1/../../../../include/c++/4.5.1/system_error:127:9: error: cannot convert 'mylib::errc::my_error' to 'std::errc' for argument '1' to 'std::error_code std::make_error_code(std::errc)'

Standard output is empty