C++ Pre-processors

There are mainly four types of Pre-processor directives in C++ programming language, and they are: -

Macros
File Inclusion
Conditional Compilation
Other directives

Macros

The macros in C/C++ programming language are one of the most exciting concepts. These are the sentences written in C++ code with the help of #define, and whenever the allocated variable is called, the value associated will be swapped and executed.

C++ code

// Here we are writing down the simple C++ programming language code snippet
// To demonstrate the concept of C/C++ preprocessors concept with their code
// and relevant display output on the compiler
#include <iostream>
 
// macro definition through a simple C++ code with #define functionality
#define LIMIT 15
// the main driver code functionality starts from here
int main()
{
    // this is simple for a loop running from 0 initially to the LIMIT
    for (int i = 0; i < LIMIT; i++) {
        std::cout << i << "\n";
    }
 
    return 0;
}

Output:

Macros with parameters C++ code

// Here we are writing down the simple C++ programming language code snippet
// To demonstrate the concept of C/C++ preprocessors concept with their code
// and relevant display output on the compiler
#include <iostream>

// macro with parameter definition 
// through a simple C++ code with #define functionality

#define AREA(l, b) (l * b)
// the main driver code functionality starts from here
int main()
{
	int l1 = 310, l2 = 35, area;

	area = AREA(l1, l2);

   // this is simple output code running whenever the macro with a parameter 
   // is executed
	std::cout << "The area of the object similar to rectangle is: " << area;

	return 0;
}

Output:

The area of the object similar to a rectangle is: 10850

2. File Inclusion

This is one of the often-seen C++ Preprocessors as we use it daily, including some built-in libraries essential for our daily basic programming needs.

Syntax

#include<file_name>
Example: 
#include<iostream>
#include<bits/stdc++.h>

3. Conditional Compilation

The Conditional unique compilation and preserved directives are an essential and integral part and parcel type of directives that help us to compile and run the specific portion of the program or a code snippet seamlessly to skip the compilation of some particular part of the program based on some conditions.

Syntax

#ifdef name_of_your _macro_created
    statement 1;
    statement 2;
    statement 3;
    statement 4;
    statement 5;
    statement 6;
    statement 7;
    .
    .
    .
    statement n;
#endif

4. Other directives

Apart from the directives in our C++ programming language, there are two mostly unknown and not so used directives #undef Directive, #pragma startup and #pragma exit: directives. Their implementation is given below

C++ code

// Here we are writing down the simple C++ programming language code snippet
// To demonstrate the concept of C/C++ preprocessors concept with their code
// and relevant display output on the compiler
#include <bits/stdc++.h>
using namespace std;
	
void function_1_is();
void function_2_is();

#pragma startup function_1_is()
#pragma exit function_2_is()

void function_1_is()
{
	cout << "Hello coder on javaTpoint.com we are inside the 1st function created now\n";
}

void function_2_is()
{
	cout << "Hello coder on javaTpoint.com we are inside the 2nd function created now\n";
}
// the main driver code functionality starts from here
int main()
{
	void function_1_is();
	void function_2_is();
	cout << "Hello coder on javaTpoint.com we are inside the int main() function now\n";

	return 0;
}

Output:

/tmp/ Lj D4 TT sh NS.o
Hello, coder on javaTpoint.com. We are inside the int primary () function now.

C++ code

// Here we are writing down the simple C++ programming language code snippet
// To demonstrate the concept of C/C++ preprocessors concept with their code
// and relevant display output on the compiler
#include <iostream>
using namespace std;

void function_1_is();
void function_2_is();

void __attribute__((constructor)) function_1_is();
void __attribute__((destructor)) function_2_is();

void function_1_is()
{
	printf("hello coder we are currently inside the function_1_is()\n");
}

void function_2_is()
{
	printf("hello coder we are currently inside the function_2_is()\n");
}

// the main driver code functionality starts from here
int main()
{
	printf("hello coder we are currently inside the int main() function\n");

	return 0;
}

Output:

hello coder we are currently inside the function_1_is()
hello coder, we are currently inside the int main() function
hello coder we are currently inside the function_2_is()

Happy Coding!

Next TopicDifference between Circular Queue and Priority Queue

← prev next →