Why won't GCC let me use a template parameter for another template's parameter?

Question

I have written the following template function for summing the contents of a std::vector object. It is in a file by itself called sum.cpp.

#include <vector>

template<typename T>
T sum(const std::vector<T>* objs) {
    T total;
    std::vector<T>::size_type i;
    for(i = 0; i < objs->size(); i++) {
        total += (*objs)[i];
    }
    return total;
}

When I try to compile this function, G++ spits out the following error:

sum.cpp: In function ‘T sum(const std::vector<T, std::allocator<_Tp1> >*)’:
sum.cpp:6: error: expected ‘;’ before ‘i’
sum.cpp:7: error: ‘i’ was not declared in this scope

As far as I can tell the reason that this error is returned is because std::vector<T>::size_type cannot be resolved to a type. Is my only option here to fall back to std::size_t (which if I understand correctly is often but not always the same as std::vector<T>::size_type), or is there a workaround?

Answer 1

typename std::vector<T>::size_type i;

http://womble.decadent.org.uk/c++/template-faq.html#disambiguation

Answer 2

size_type is a dependent name, you need to prefix it with typename, i.e.:

typename std::vector<T>::size_type i;