Question

I have the following template:

#include <iostream> 
template <class T,T defaultVal, int dim=255> 
class Vec 
{ 
    T _vec[dim]; 
    int _dim; 
public: 
    Vec () : _dim(dim) 
    { 
        for (int i=0;i<_dim;++i) 
        { 
            _vec[i] = defaultVal; 
        } 
    } 
    ~Vec () {}; 
    // other operators and stuff 
}; 
int main () 
{ 
    int defValue = 0; 
    Vec < int,defValue > vecWithDefVal; 
}

But the program will not compile because a template value must be known during compilation time, meaning const or const-literal.

I really dont understad this error, can anyone explain it to me?

Answer 1

Template class is created at compile time, so the value has to be known at compile time. If it is not const it is not known until run-time, so the compiler can’t create the template class.