CODEWITHSUNDEEP
c++stlvectorpolymorphismforeach
Gal Goldman
Gal Goldman

Reputation: 8869

Using std::for_each on polymorphic method in c++

When using the std::for_each, 

class A;
vector<A*> VectorOfAPointers;

std::for_each(VectorOfAPointers.begin(), VectorOfAPointers.end(), std::mem_fun(&A::foo));

If we have classes inheriting from A and implementing foo(), and we hold a vector of pointers to A, is there any way to call a polymorphic call on foo(), rather then explicitly calling A::foo()? Note: I can't use boost, only standard STL.

Thanks, Gal

Upvotes: 3

Views: 1887

Answers (1)

vava
vava

Reputation: 25371

It actually works this way.

#include <algorithm>
#include <iostream>
#include <functional>
#include <vector>

struct A {
    virtual void foo() {
        std::cout << "A::foo()" << std::endl;
    }
};
struct B: public A {
    virtual void foo() {
        std::cout << "B::foo()" << std::endl;
    }
};

int main()
{
    std::vector<A*> VectorOfAPointers;
    VectorOfAPointers.push_back(new B());
    std::for_each(VectorOfAPointers.begin(), VectorOfAPointers.end(), std::mem_fun(&A::foo));
    return 0;
}

prints

B::foo()

So it does exactly what you want. Check that virtual keywords are present though, it's easy to forget them.

Upvotes: 11

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