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FIFO Example in the C Language

FIFO is an acronym that means "First In, First Out." It is a data structure handling method in which the first element is handled first, and the last element is handled last.

It is a way of arranging the processing of a data structure (usually a data buffer) in which the initial entry, or "head," of the queue is handled first.

FIFO Real-life Example:

Consider the following series of points:

  1. Assume there is a ticket counter. People arrive at the counter, grab their tickets, and leave.
  2. People form a line (queue) to go to the ticket booth in an ordered way.
  3. The individual who enters the queue first will receive the ticket and exit first.
  4. The next person in line will receive the tickets after the one in front of them.
  5. As a result, the person who arrives last in the queue (line) will receive the tickets last. 
  6. Hence, the first person in line (queue) receives the ticket first, and the last person in line (queue) receives the ticket last.

This is known as the "First-In-First-Out" (FIFO) method.

The queue has two ends, one at the front and one at the back.

Many programs are built on the “First-In-First-Out” (FIFO) principle.

Where does FIFO come into play?

  1. Communication and Networking: FIFOs are used in computer networks to store data packets that are ready to travel to their next destination via the communication network's bridges, switches, and routers.
  2. Data Structures: Certain data structures, such as "queue" and its variants, process data using the FIFO method.
  3. Disk Scheduling: Disk controllers can utilize the First-In-First-Out (FIFO) method as a disk scheduling technique to decide the order in which disk I/O requests should be handled.

Syntax for FIFO

A function call, such as "mkfifo," is used to create a "First-In-First-Out" (FIFO) file.

int mkfifo(const char *file_pathname, mode_t method); 

mkfifo() creates a First-In-First-Out (FIFO) special file with the name "file_pathname," where "method" determines the permissions of the FIFO. It is updated in the normal way by the process's umask: the permissions of the generated file are "method & umask."

Using First-In-First-Out (FIFO) in the C Programming Language:

Because named pipes (FIFO) are files, we can utilize all of the system methods associated with them, such as "open," "read," "write," and "close."


The following represents the FIFO Page Replacement Algorithm.

Step 1: Start

Step 2: Begin to browse the pages.

Step 3: If the memory has fewer pages, the capacity is reduced; otherwise, the process proceeds to Step 5.

Step 4: Push pages into the queue (line) one at a time till the queue is full or all the page requests are satisfied.

Step 5: Do nothing if the existing page is still in memory.

Step 6: Otherwise, pop the first page from the line (queue) because it was placed first.

Step 7: Replace the first page in the string with the existing page.

Step 8: Increase the number of page faults. (Increment)

Step 9: Stop


This following program code represents the most basic page replacement approach, in which the OS (operating system) system keeps all pages in a queue. The first pages are maintained at the beginning, while the last pages are kept at the end. When a page fault occurs, the front pages are deleted first, followed by the pages in demand.

/* C program for FIFO page replacement algorithm */
#include <stdio.h>
int main(){
   	int Incoming_Stream[] = {10, 20, 30, 40, 50};
    	int page_Faults = 0;
    	int frame = 5;
    	int a, b, s, pages;
pages = sizeof(Incoming_Stream)/sizeof(Incoming_Stream[0]);
printf("Incoming \t Frame 1 \t Frame 2 \t Frame 3 \t Frame 4 \t Frame 5");	
int temp[frame];
   	for(a = 0; a < frame; a++){
       		temp[a] = -1;
for(a = 0; a < pages; a++){
       		s = 0;
                      for(b = 0; b < frame; b++){
            		if(Incoming_Stream[a] == temp[b]){
        		if((page_Faults <= frame) && (s == 0)){
            		temp[a] = Incoming_Stream[a];
        		else if(s == 0){
            		temp[(page_Faults - 1) % frame] = Incoming_Stream[a];
        		for(b = 0; b < frame; b++){
            		if(temp[b] != -1){
                			printf(" %d\t\t\t", temp[b]);
          				printf(" - \t\t\t");
printf("\nTotal Number of Page Faults:%d\n", page_Faults);
   	return 0;


FIFO Example in the C Language