Question

Problem is as follow: The following test throws huge amounts of compiler errors.

#include <vector>
using namespace std;

template<class T>
class test{
   vector<T> vec;
public:
   vector<T>::iterator begin();

};

template<class T>
vector<T>::iterator test<T>::begin(){
  return vec.begin();
}

int main(){

  test<float> testing;
  testing.begin();

}

Some Compiler errors:

 test.cpp(8): warning C4346: 'std::vector<T>::iterator' : dependent name is not a type
 test.cpp(8): error C2146: syntax error : missing ';' before identifier 'begin'
 test.cpp(13): error C2143: syntax error : missing ';' before 'test<T>::begin'

However, if you swap out the templated vector<T> for say, vector<float> its compiles just fine. For example:

template<class T>
class test{
   vector<T> vec;
public:
   vector<float>::iterator begin();

};

template<class T>
vector<float>::iterator test<T>::begin(){
   return vec.begin();
}

Any ideas as to why?

Answer 1

You need to add typename in two places:

typename vector<T>::iterator begin();

and

typename vector<T>::iterator test<T>::begin()

By adding typename, you are telling the compiler how to parse the code. Basically, by adding typename, you are telling the compiler to parse the declaration as a type.

Please read Where and why do I have to put the “template” and “typename” keywords? for an in-depth explanation.