Importance of function template

A function template defines one generic function for any data type, using a type parameter T. Its importance:

• Code reuse – one definition replaces many overloaded functions that differ only in data type.
• Less effort and fewer errors – logic is written and debugged once.
• Type safety – unlike macros or void*, the compiler checks types.
• Easy maintenance – a change in logic is made in one place.
• No run-time cost – the compiler generates the needed version at compile time.

Example

Without templates we need swap for int, float, char, etc. With a template:

#include <iostream>
using namespace std;

template <class T>
void swapValues(T &a, T &b) {
    T temp = a;
    a = b;
    b = temp;
}

int main() {
    int x = 5, y = 9;
    float p = 1.5f, q = 2.5f;
    swapValues(x, y);          // T = int
    swapValues(p, q);          // T = float
    cout << x << " " << y << endl;   // 9 5
    cout << p << " " << q << endl;   // 2.5 1.5
    return 0;
}

One function serves both int and float.