Difference between Preprocessor Directives and Function Templates in C++

In this article, we will discuss about the preprocessor directives and function template in C++. But before discussing their differences, we must know about the preprocessor directives and function template.

What are Preprocessor Directives?

Preprocessor programs give preprocessor directives that instruct the compiler to process the source code without compiling it. All of these directives from the preprocessor begin with a '#' (hash) symbol. The '#' sign indicates that the preprocessing program will process any statement that begins with a '#'. These preprocessing directives can be used anywhere in our software. Some preprocessing directives are #include, #define, #ifndef, etc.

The '#' symbol provides a route to the preprocessor and a command like include is handled by the preprocessor program. For example, the #include is going to include the code or contents of the specified file in the application.

Example:

Let us take an example to illustrate the use of preprocessor directives in C++.

// 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 is a very powerful tool. The simple idea is to give the data type as a parameter to avoid writing the same code for several data types. For example, the function sort() may be required for several data types by a software firm. We can construct a single sort() function and send the datatype as an argument instead of creating and maintaining numerous scripts.

Example:

Let us take an example to illustrate the use of function templates in C++.

// 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

Using the function template, we can create generic functions that may operate on any data. For instance, the function template that determines the minimum of two values of any kind may be defined as follows:

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

However, preprocessor directives made using preprocessor directive #define can also be used to do this work. Thus, we can define the minimum of the two integers as follows:

Most of us prefer to utilize templates in C++ instead of pre-processor directives because:

Type checking is not included for Pre-processor directives. However, in the case of templates, the compiler does complete type verification.
Pre-processor directives may call for unexpected resul

Key Differences between the Preprocessor directives and Function templates:

Difference between Preprocessor Directives and Function Templates in C++

There are several differences between Preprocessor directives and function templates. Some main differences between Preprocessor directives and function templates are as follows:

Aspect	Pre-processor Directives	Function Templates
Purpose	Text Modification: Source code is manipulated prior to compilation with preprocessor directives. Tasks like macro definitions, conditional compilation, and file inclusion are under their purview.	Generic Programming: Function templates are a tool used in generic programming to create functions that handle a variety of data types. They enable the creation of algorithms that don't duplicate code when they adapt to various kinds.
Activation	Time of Compilation: Completed prior to the beginning of the compilation process. Before the code is given to the compiler, they make changes to it.	Time of Compilation: After the preprocessor completes its work, compilation occurs during this process stage.
Syntax and Scope	Syntax: Starts with the # symbol and goes on to include, define, ifdef, etc. Scope: All of the file in which they are specified. They work with the complete file of codes.	Syntax: Generic types come after the template keyword in the definition. Scope: Local inside the class or function in which they are declared is their scope.
Constraints	They have a limited comprehension of C++ syntax and semantics because they only work at a textual level and are not fully aware of the code's structure.	Restricted to Types: Although flexible with respect to various data formats, they may not be as flexible with respect to various functionality or algorithms.
Usage:	It is mainly used for defining constants, conditional compiling based on flags, and the creation of macros that substitute text. It is also used for incorporating header files.	It is used to write functions that don't require duplicate code to work on diverse data formats. Suitable for general algorithms such as searching, sorting, etc.
Debugging:	Debugging might be difficult because of direct text replacement. Errors may be more difficult to identify because preprocessing may alter the code's appearance.	Compared to preprocessing directives, they are simpler to debug since they are a part of the produced code and preserve the original template's structure, making mistake detection and correction easier.