How to Resolve Overloaded Function Ambiguity in std::for_each()?

Pointer to Overloaded Function in std::for_each() Algorithm

In C , it is possible to have functions with the same name but different parameters, known as function overloading. This can introduce ambiguity when passing an overloaded function as an argument to a function such as std::for_each().

Issue:

Consider the following code snippet:

class A {
    void f(char c);
    void f(int i);

    void scan(const std::string& s) {
        std::for_each(s.begin(), s.end(), f);
    }
};

In this example, the scan() method attempts to pass the overloaded function f() to std::for_each(). However, the compiler cannot automatically determine which overload of f() to use.

Solution:

To specify the desired overload, you can use static_cast<>() or the mem_fun() function pointer.

Method 1: Static_Cast<>()

// Uses the void f(char c); overload
std::for_each(s.begin(), s.end(), static_cast<void (*)(char)>(&f));
// Uses the void f(int i); overload
std::for_each(s.begin(), s.end(), static_cast<void (*)(int)>(&f));

By casting the function pointer to a specific type, you force the compiler to resolve the overload based on the given function signature.

Method 2: Mem_Fun()

If f() is a member function, you can use the mem_fun() function pointer:

std::for_each(s.begin(), s.end(), std::mem_fun(&A::f));

This approach requires you to specify the class name and the overload, which can be more verbose but also more flexible.

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