C++ Exceptions; int or std::exception?

I am writing some library functions that needs to do some error reporting. I want to use exceptions rather than return values.

I wrote my functions that throws int exceptions.

Eg:

if(strm->atEnd()){
    // unexpected end of stream
    throw -2;
}

My question is, is this method OK? Or should I throw a exception derived from std::exception?

In what way is throwing a std::exception better? (Other than being able to use catch(std::exception &e))

Is throwing int exceptions bad practice? (all throw int values are documented in doxygen comments)

I can't find any reason as to why (in this case) should I throw an object.