Question

Why does the following not compile (MSVC10 – but I suspect it’s not valid C++), and is there a workaround?

template <typename M>
struct MyClass
{
    typedef std::vector<M>::iterator iteratorT;

    iteratorT myIterator;

};

Error is error C2146: syntax error : missing ';' before identifier 'iteratorT'. I’ve tried a bunch of variations with the same result: you can use std::vector<M>::iterator as a type in a member function, but not as a type of a member variable.

Answer 1

It’s a case of the typename. Short answer, you need to do this instead:

 typedef typename std::vector< M >::iterator iteratorT;

Long answer, the compiler doesn’t know what std::vector< M >::iterator resolves to as M can be anything and there could be a specialization of std::vector for it. Specifically, it cannot tell if std::vector< M >::iterator is a type or a value, and it believes its a value. You have to explicitly tell the compiler its a type by inserting typename.