C program to reverse the content of the file and print it

17 Feb, 2022
Given a text file in a directory, the task is to print the file content backward i.e., the last line should get printed first, 2nd last line should be printed second, and so on.Examples:  
Input: file1.txt has: Welcome to GeeksforGeeks Output: GeeksforGeeks to WelcomeGeeksforGeeks Input: file1.txt has: This is line one This is line two This is line three This is line four This is line five Output: This is line five This is line four This is line three This is line two This is line one  
 
Approach:  
Initialise previous length of the text as 0.Find the length of the current line and add it to the previous length. This given the next starting index of the new line.Repeat the above steps till the end of the file.Initialise the array of length of the given message in the given file.Now rewind your file pointer and place the last pointer of the text to arr[K – 1] where K is the length of the array using fseek().Print the length of the last line and decrease K by 1 for printing the next last line of the file.Repeat the above steps until K is equals to 0.
Initialise previous length of the text as 0.
Find the length of the current line and add it to the previous length. This given the next starting index of the new line.
Repeat the above steps till the end of the file.
Initialise the array of length of the given message in the given file.
Now rewind your file pointer and place the last pointer of the text to arr[K – 1] where K is the length of the array using fseek().
Print the length of the last line and decrease K by 1 for printing the next last line of the file.
Repeat the above steps until K is equals to 0.
Below is the implementation of the above approach: 
C
// C program for the above approach#include <stdio.h>#include <string.h>#define MAX 100 // Function to reverse the file contentvoid reverseContent(char* x){     // Opening the path entered by user    FILE* fp = fopen(x, "a+");     // If file is not found then return    if (fp == NULL) {        printf("Unable to open file\n");        return;    }     // To store the content    char buf[100];    int a[MAX], s = 0, c = 0, l;     // Explicitly inserting a newline    // at the end, so that o/p doesn't    // get effected.    fprintf(fp, " \n");    rewind(fp);     // Adding current length so far +    // previous length of a line in    // array such that we have starting    // indices of upcoming lines    while (!feof(fp)) {        fgets(buf, sizeof(buf), fp);        l = strlen(buf);        a = s += l;    }     // Move the pointer back to 0th index    rewind(fp);    c -= 1;     // Print the contents    while (c >= 0) {        fseek(fp, a, 0);        fgets(buf, sizeof(buf), fp);        printf("%s", buf);        c--;    }     return ;} // Driver Codeint main(){    // File name in the directory    char x[] = "file1.txt";     // Function Call to reverse the    // File Content    reverseContent(x);    return 0;}
Input File:  
Output File:  
 
nikhatkhan11
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