Question

I started learning about templates and I copied the code from my book but the compiler is giving me this error

Error 1 error: ‘swap’ : ambiguous call to overloaded function”

Here is my program

#include <iostream>

template <typename X>
void swap(X &a, X &b);

int _tmain(){
    using namespace std;
    int a, b;

    cout << "enter two numbers:\n";
    cin >> a >> b;
    cout << "Your numbers are: " << a << ", " << b << endl;

    swap(a, b); //error is here
    cout << "Your numbers reversed are: " << a << ", " << b << endl;

    return 0;
}

template <typename X>
void swap(X &a, X &b){
    X temp = a;
    a = b;
    b = temp;
}

Answer 1

You are redefining the function swap with the same signature, so you’re having an ambiguous definition of it, and, consequently, an ambiguous call.

If you want to maintain the function with the same signature, you should either choose to use not the “using namespace std;”, which will not shadow your swap() definition, or simply define tthe function in another namespace.

Example:

namespace your_namespace {

    template <typename X>
    void swap(X &a, X &b) {
        X temp = a;
        a = b;
        b = temp;
    }

}

int foo(10), bar(20);
std::cout << "foo: " << foo << "; bar: " << bar << std::endl;

your_namespace::swap(foo, bar);
std::cout << "foo: " << foo << "; bar: " << bar << std::endl;

Output:

foo: 10; bar: 20
foo: 20; bar: 10

Regards!