Question about vector iterator in template functions

Question

I'm trying to learn the STL library and I'm having a weird problem. This code compiles perfectly:

void Show(vector<int> myvec) {     vector<int>::iterator it;     cout << "Vector contains:";     for( it = myvec.begin(); it < myvec.end(); it++)      {          cout << " " << *it;     }     cout << endl; } 

while this one gives me an error message at compile time:

template <class T>  void Show2(vector<T> myvec) {     vector<T>::iterator it;     cout << "Vector contains:";     for( it = myvec.begin(); it < myvec.end(); it++)     {          cout << " " << *it;     }     cout << endl; } 

The error is:

$ g++ hello.cpp hello.cpp: In function ‘void Show2(std::vector<T, std::allocator<_Tp1> >)’: hello.cpp:19: error: expected ‘;’ before ‘it’ hello.cpp:21: error: ‘it’ was not declared in this scope 

It seems a very simple mistake, but I couldn't find it.

Answer 1

You need to say typename vector<T>::iterator it.

On another note, you're passing vectors by value. That means the entire vector gets copied in the function call. void Show(vector<T> const &myvec) and using const_iterator would be wiser.

Answer 2

You need this:

typename vector<T>::iterator it; 

This tells the compiler that vector<T>::iterator should be treated as a type, something it can't assume since iterator is dependent on what T is.