Question

template<class U, class W>
std::ostream& operator<<( std::ostream & out, const Alias<U, W> & A)
{
    out<<A.ItoS.size()<<std::endl;
    for (std::map<W, U>::const_iterator it = A.ItoS.begin(); it != A.ItoS.end(); it++)
        out<<it -> first<<" "<<it -> second<<std::endl;
    return out;
}

errors are on line :
for (std::map<W, U>::const_iterator it = A.ItoS.begin(); it != A.ItoS.end(); it++)

error: expected ‘;’ before ‘it’

error: ‘it’ was not declared in this scope

Other class functions dont’t have any compilation problems.

While I was using std::string instead of U and int instead of W everything was fine.
I am using Codeblocks 10 with MinGW compiler.

Answer 1

You forgot typename here:

  typename std::map<W, U>::const_iterator it = A.ItoS.begin();
//^^^^^^^

const_iterator is a dependent name, therefore typename is required here. For detail explanation, read this topic:

• Where and why do I have to put the "template" and "typename" keywords?

In C++11, you could simply write:

 auto it = A.ItoS.begin();

which is a relief to C++ programmers!