data member 'vec' cannot be a member template

Question

I have the following two lines in a header in order to declare a vector containing a template:

template <class t>
std::vector <t> vec;

However I get the following error:

data member 'vec' cannot be a member template

What did I do wrong?

Edit: I don't know that I was understood correctly, I am trying to declare a vector which contains a template, I know that this can be done since one can have the following:

template <class T>
void funct(vector <T> v){

}

This function takes a vector of a template as its parameter. I wish to do the same thing except with declaring the vector in a header in order to allow the vector to contain anything.

Answer 1

Such a vector can't contain anything.

Let's suppose that a compiler lets you declare such a vector and you write:

//...
A Aobj;
vec.push_back(Aobj);
//...

Then the size of one element in vec will be the sizeof(A). But next you write:

//...
B Bobj;
vec.push_back(Bobj);
//...

What will the size of one element here be?

Anyway, as a workaround you may declare vector<void*> vec so the vector can contain a pointer to anything you want.

Answer 2

The template <> statement is only used when declaring a function template or a class template. For example you can use it when you declare (and define) a class:

template <typename T>
class TemplateClass {
    /* definition */
};

Or a function:

template <typename T>
void templateFunc(T value) {
    /* definition */
}

When creating an instance of the class, you can't use the template <> statement. Instead you specify a template parameter like this:

TemplateClass<int> tc;

And when calling a template function:

int i = 1;
templateFunc(i); // <-- Automatic template deduction to int.