How do i output contents of a map using operator <<

Question

I'm trying to output the contents of my map but i'm not sure on how to go about it. i've got the following declarations for a map and a iterator set as private in my header file

typedef map<long, string> Student;
Student newstudent;
typedef Student::const_iterator studentItr;
studentItr itr;

and i have the following declaration in my .cpp

map<long, string> classname::GetMap()
{
    for(itr = newstudent.begin(); itr !=newstudent.end(); itr++)
{
    cout << itr->first << " => " <<itr->second << '\n';
}

    return newstudent;
}

and this is how i'm trying to pass this into my overloaded operator << function

ostream & operator <<( ostream & os, classname & R)
{
    os << " " << R.GetMap() << '\n';

    return os;
}

Usually this would work for any other function but since its a map i get the following error:

no match for 'operator<<' (operand types are 'std::basic_ostream< char >' and 'std::map < long int, std::__cxx11::basic_string< char > > ')|

Could anybody point me in the right direction of what i'm doing wrong

EDIT: Thanks for posting your suggestions i appreciate the help, but i think something isnt right either with my complier or with how i've stated something.

Everytime i try using Student as a type it wont register as a type and i get an error about it.

E.g if i declare this statement

ostream & operator <<( ostream & os, const Student & R)

OR

Student & classname::GetMap()

i get the error:

'Student' does not name a type

This error ultimately is leading to nothing within my statements making any sense and i'm not sure how to fix that

Answer 1

So you seem to have put the output code inside for GetMap function for some reason. Either you want a routine called GetMap which just gets a map, or you want a routine called PrintMap (for instance) which outputs the map. You have half and half. Here's one way to do it

void classname::PrintMap() const
{
    for(itr = newstudent.begin(); itr !=newstudent.end(); itr++)
    {
        cout << itr->first << " => " <<itr->second << '\n';
    }
}

ostream & operator <<( ostream & os, classname & R)
{
    os << " ";
    R.printMap();
    os << '\n';
    return os;
}

This could be improved, for instance you could pass the stream you want to output to, to the PrintMap function. Like this

void classname::PrintMap(ostream & os) const
{
    for(itr = newstudent.begin(); itr !=newstudent.end(); itr++)
    {
        os << itr->first << " => " <<itr->second << '\n';
    }
}

ostream & operator <<( ostream & os, classname & R)
{
    os << " ";
    R.printMap(os);
    os << '\n';
    return os;
}

FInally you could follow the common convention and rename PrintMap as operator<< and make it a friend function instead of a member function.

Student& classname::GetMap()
{
    return newstudent;
}

ostream & operator<<(ostream & os, const Student& s)
{
    for(itr = s.begin(); itr !=s.end(); itr++)
    {
        os << itr->first << " => " <<itr->second << '\n';
    }
    return os;
}

ostream & operator <<( ostream & os, classname & R)
{
    os << " " << R.getMap() << '\n';
}

Answer 2

You could make an operator << for your map type. (totally untested code)

ostream & operator <<( ostream & os, const Student & R) {
    for(studentIter itr = R.begin(); itr !=R.end(); itr++){
        os << itr->first << " => " <<itr->second << '\n';
    }
    return os;
}

Edit: Changed the names to match those in your question.