C program to remove specific line from a file

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Write a C program to remove a given line from a file. How to remove a given line from a text file in C programming. Logic to remove specific line from a file in C program.

In previous post I explained to remove a word from file. In this post we will continue further and will learn to remove a given line from file. Logic to remove word or line from a file are alike. So, lets get started and code it.

Required knowledge

Basic Input Output, Pointers, Strings, Functions, File Handling

Logic to remove specific line from a file

Step by step descriptive logic to remove a given line from file.

  1. Input file path and line number to remove from user. Store it in some variable say path and line.
  2. Open file in r (read) mode, store its reference in srcFile.
  3. Create and open a temporary file in w (write) mode. Store its reference in tempFile.
  4. Initialize a count = 1 variable to keep track of current line number of source file.
  5. Read a line from source file srcFile. Store it in some variable say buffer.
  6. If current line number is not equal to line to remove i.e. if(line != count) then write buffer to tempFile.
  7. Increment count++.
  8. Repeat step 5-7 till end of source file.
  9. Close both files i.e. srcFile and tempFile.
  10. Delete our original source file srcFile.
  11. Rename temporary file with source file path.

I have used functions for this program, since it provides modularity. I have created two functions deleteLine() and printFile() to delete a given line and print a given file on console.

Program to remove specific line from a file

/**
 * C program to delete specific line from a file.
 */

#include <stdio.h>
#include <stdlib.h>

#define BUFFER_SIZE 1000

/* Function declarations */
void deleteLine(FILE *srcFile, FILE *tempFile, const int line);
void printFile(FILE *fptr);


int main()
{
    FILE *srcFile;
    FILE *tempFile;

    char path[100];

    int line;


    /* Input file path and line number */
    printf("Enter file path: ");
    scanf("%s", path);

    printf("Enter line number to remove: ");
    scanf("%d", &line);


    /* Try to open file */
    srcFile  = fopen(path, "r");
    tempFile = fopen("delete-line.tmp", "w");


    /* Exit if file not opened successfully */
    if (srcFile == NULL || tempFile == NULL)
    {
        printf("Unable to open file.\n");
        printf("Please check you have read/write previleges.\n");

        exit(EXIT_FAILURE);
    }



    printf("\nFile contents before removing line.\n\n");
    printFile(srcFile);


    // Move src file pointer to beginning
    rewind(srcFile);

    // Delete given line from file.
    deleteLine(srcFile, tempFile, line);


    /* Close all open files */
    fclose(srcFile);
    fclose(tempFile);


    /* Delete src file and rename temp file as src */
    remove(path);
    rename("delete-line.tmp", path);


    printf("\n\n\nFile contents after removing %d line.\n\n", line);

    // Open source file and print its contents
    srcFile = fopen(path, "r");
    printFile(srcFile);
    fclose(srcFile);

    return 0;
}


/**
 * Print contents of a file.
 */
void printFile(FILE *fptr)
{
    char ch;

    while((ch = fgetc(fptr)) != EOF)
        putchar(ch);
}



/**
 * Function to delete a given line from file.
 */
void deleteLine(FILE *srcFile, FILE *tempFile, const int line)
{
    char buffer[BUFFER_SIZE];
    int count = 1;

    while ((fgets(buffer, BUFFER_SIZE, srcFile)) != NULL)
    {
        /* If current line is not the line user wanted to remove */
        if (line != count)
            fputs(buffer, tempFile);

        count++;
    }
}

Output

Enter file path: data\file3.txt
Enter line number to remove: 2

File contents before removing line.

I love programming.
I am learning C programming at Codeforwin.
Programming with files is fun.
Learning C programming at Codeforwin is simple and easy.



File contents after removing 2 line.

I love programming.
Programming with files is fun.
Learning C programming at Codeforwin is simple and easy.

Happy coding 😉

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