std::map::const_iterator template compilation error

Question

I have a template class that contains a std::map that stores pointers to T which refuses to compile:

template 
class Foo
{
public         


        

Answer 1

You need:

typename std::map<int, T*>::const_iterator begin() const { return items.begin(); }

Or simpler

typedef typename std::map<int, T*>::const_iterator const_iterator;
const_iterator begin() const { return items.begin(); }

This is because const_iterator is dependent name on T so you need to tell compiler that it is actually type.

Answer 2

Use typename:

typename std::map<int, T*>::const_iterator begin() const ...

When this is first passed by the compiler, it doesn't know what T is. Thus, it also doesn't know wether const_iterator is actually a type or not.

Such dependent names (dependent on a template parameter) are assumed to

• not be types unless prefixed by typename
• not to be templates unless directly prefixed by template.

Answer 3

You need typename:

typename std::map<int, T*>::const_iterator begin() const { return items.begin(); }