Difference Between Preprocessor Directives And Function Templates In C++

In this guide, we will explore the concept of preprocessor directives and function templates in C++. Prior to delving into their distinctions, it is essential to have a solid understanding of both preprocessor directives and function templates.

What are Preprocessor Directives?

Preprocessor software provides preprocessor commands that guide the compiler in handling the source code without actual compilation. Each of these commands from the preprocessor starts with a '#' (hash) character. The presence of the '#' symbol signifies that the preprocessor will handle any instruction starting with '#'. These preprocessing commands are applicable in various sections of our software. A few examples of preprocessing commands are #include, #define, #ifndef, and so forth.

The '#' symbol functions as an entry point to the preprocessor, where directives like include are managed by the preprocessor software. For instance, the #include directive is responsible for integrating the code or material from the designated file into the application.

Example:

Let's consider a scenario to demonstrate the application of preprocessor directives in the C++ programming language.

// Program to implement preprocessor directories
#include <bits/stdc++.h>

#define min(l, m) ((l < m) ? l : m)

using namespace std;

// Driver code
int main()
{
	int l = 89, m= 90;

	// min value among both
	cout << "The Min value is: "
		<< min(l, m);

	return 0;
}

Output:

The Min value is: 89

What are Function Templates?

In C++, a template serves as a highly effective mechanism. The basic concept involves providing the data type as an input to prevent redundancy in coding for multiple data types. For instance, a software company might need the sort function for various data types. Instead of managing multiple scripts, a unified sort function can be developed where the data type is passed as an argument.

Example:

Let's consider an example to demonstrate the application of function templates in the C++ programming language.

// Program to implement templates in c++
#include <iostream>
#include <stdio.h>
using namespace std;

// template
template <class Tem>
Tem Min(Tem l, Tem m)
{
	return (l < m) ? l : m;
}

// Driver Code
int main()
{
	int l = 80, m = 56;

	// display of min value
	cout << "The Minimum value of both is: " << min(l, m);

	return 0;
}

Output:

The Minimum value of both is: 56

By utilizing the function template, we have the capability to generate versatile functions that can manipulate various types of data. For example, a function template designed to find the smallest value between two inputs of any data type can be established in the following manner:

template <class Temp>
Temp minimum(Temp x, Temp y)
{
   return (x < y) ? x : y;
}

However, preprocessor directives created with the #define preprocessor directive can also accomplish this task. Therefore, we can declare the smaller of the two integers in the following manner:

#define minimum(x, y) ((x < y) ? x: y)

Most individuals opt for using templates in C++ over pre-processor directives due to the following reasons:

• ✅ Pre-processor directives lack type checking, whereas templates allow the compiler to perform full type verification.
• ✅ Pre-processor directives can lead to unforeseen outcomes.

Key Differences between the Preprocessor directives and Function templates:

There exist numerous distinctions between Preprocessor directives and function templates. A few key variances between Preprocessor directives and function templates include: