C++ template gotchas

Question

just now I had to dig through the website to find out why template class template member function was giving syntax errors:

template class F00         


        

Answer 1

The star of questions about templates here on SO: the missing typename!

template 
class vector
{
  public:
    typedef T * iterator;
    ...
};

template 
void func()
{
    vector::iterator it;           // this is not correct!

    typename vector::iterator it2; // this is correct.
}

The problem here is that vector::iterator is a dependent name: it depends on a template parameter. As a consequence, the compiler does not know that iterator designates a type; we need to tell him with the typename keyword.

The same goes for template inner classes or template member/static functions: they must be disambiguated using the template keyword, as noted in the OP.

template 
void func()
{
    T::staticTemplateFunc();          // ambiguous

    T::template staticTemplateFunc(); // ok

    T t;

    t.memberTemplateFunc();          // ambiguous

    t.template memberTemplateFunc(); // ok
}