pass "pointer to pointer" to a template function

Question

I have a funtion which allocates memory to a pointer as following:

   void initializeImageBuffer(unsigned char **image, int w, int h)
   {
        if (*image != NULL)
            delete[] *image;
        *image = new unsigned char[w * h];
   }

now I want to generalize the argument type (unsigned char/int/double) using function template. Thats what I did:

 template<typename T, int, int>
 void initializeImageBuffer(T **image, int w, int h)
   {
        if (*image != NULL)
            delete[] *image;
        *image = new T[w * h];
   }

But there is an error using the function like:

    unsigned char* image;
    initializeImageBuffer(&image, 200, 200);

"There is no instance of overloading function with these argument types. The Arguments types are (unsigned char**, int, int)."

Answer 1

template<typename T, int, int>

Here you declare that your template has three parameters, the type T and two unnamed ints. Since there is no way to deduce the value of the ints at the call site, you would need to provide them explicitly, along with T since you can only provide template arguments from left to right:

initializeImageBuffer<unsigned char, 42, 42>(&image, 200, 200);

However, what you most probably want is just to drop these ints, they have absolutely no use here.

template<typename T>
void initializeImageBuffer(T **image, int w, int h)