Storing Function Pointers

To store multiple function pointers of the same type in a collection, you can use the same type alias approach we showed in the lesson. For example:

1#include <iostream>
2#include <vector>
3
4using IntPredicate = bool (*)(int);
5
6bool isEven(int n) { return n % 2 == 0; }
7
8bool isPositive(int n) { return n > 0; }
9
10int main() {
11  std::vector<IntPredicate> Predicates{
12    isEven, isPositive};
13
14  for (auto& Pred : Predicates) {
15    std::cout << std::boolalpha;
16    std::cout << Pred(4) << '\n';   
17    std::cout << Pred(-1) << '\n';  
18  }
19}

1true
2false
3false
4false

Here, we define an IntPredicate type alias for a function pointer that takes an int and returns a bool. We can then use this alias to specify the type stored in our vector.

We populate the vector with our isEven and isPositive function pointers. Later, we can iterate over the vector and call each function pointer with the () operator, just like we would with a normal function.

This same approach works for arrays and other collections that can store the function pointer type.