Question

Let us suppose that we have a function of n variables

y = f (x1, ..., xn) 

Such a function I would like to pass as an argument.

In Matlab the following construction using a handle is available:

function y=func(x)
y = sin(x(0)) * cos(x(1))  //Any definition, not important

p_func=@func; //Define handle

It is possible to use the handle as a parameter of another function:

y = function2(p_func, n);

where n represents a dimension…

How to rewrite this code using C++? We use a simple model with the function template

temmplate <typename T>
T func( const T *arg, const short n) {return sin(arg[0]) * cos(arg[1])};

where xi arguments are represented by the 1-dimensional array of n elements. The problem is that in this case it is not possible to use a pointer to the function template

template <class T>
static T ( *pfunc ) ( const T *arg, const short n )

only a specialization… Perhaps another model could be more appropriate…Thanks for your help…

Remark:
I know that a class template is useful

template  <typename T>
class Foo
{ 
    T func( const T *args, const short n);
};

and this construction works:

template <class T>
static T ( *pfunc ) ( const T *arg, const short n )

But it may not be used in the current model of the library (I can not affect this).

Answer 1

C++ is a statically typed language. Every object in C++, whether a function pointer, or whatever, must have a specific type. And the type of a function pointer is based on the types of arguments that the function to be pointed to is given.

A template is not an object, so you can’t get a pointer to one. You can get a pointer to an instantiation of a template. Using your func definition, func<int> is a function that takes a const int* and a short. You can get a pointer to func<int>. But func is a template; you can’t get a pointer to a template.

That’s why C++ programs often throw functors around instead of function pointers. Functors can have a template operator() method, so you can call them as though you were passing around template functions. But since you say that you have to use a function pointer, there’s not much that can be done.