C program to remove a word from text file

Categories C programming 4 mins read

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

C programming support overwrite, insert and append operations on file content. It does not support delete operation. You cannot delete file contents directly. In this post I will explain you how to delete a word from file in C.

Required knowledge

Basic Input Output, String, File Handling

Logic to remove word from file

Step by step descriptive logic to remove a word from text file.

  • Open source file in r (read) mode. Store its reference in a FILE pointer variable say fPtr.
  • Create and open a temporary file say delete.tmp in w (write) mode. Store its reference in a variable say fTemp.
  • Read word to remove from user in some variable say toRemove.
  • Read a line from source file fPtr and store it in temporary buffer variable.
  • Remove all occurrence of given word from buffer and write buffer to temporary file fTemp.
  • Repeat step 4-5 till end of source file.
  • Close both file fPtr and fTemp.
  • Delete source file using remove() function.
  • Rename temporary file with source file name using rename() function. And we are done.

Program to remove word from file

/**
 * C program to delete a word from file.
 */

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

#define BUFFER_SIZE 1000


void removeAll(char * str, const char * toRemove);


int main()
{
    FILE * fPtr;
    FILE * fTemp;
    char path[100];
    
    char toRemove[100];
    char buffer[1000];


    /* Input source file path path */
    printf("Enter path of source file: ");
    scanf("%s", path);

    printf("Enter word to remove: ");
    scanf("%s", toRemove);


    /*  Open files */
    fPtr  = fopen(path, "r");
    fTemp = fopen("delete.tmp", "w"); 

    /* fopen() return NULL if unable to open file in given mode. */
    if (fPtr == NULL || fTemp == NULL)
    {
        /* Unable to open file hence exit */
        printf("\nUnable to open file.\n");
        printf("Please check whether file exists and you have read/write privilege.\n");
        exit(EXIT_SUCCESS);
    }


    /*
     * Read line from source file and write to destination 
     * file after removing given word.
     */
    while ((fgets(buffer, BUFFER_SIZE, fPtr)) != NULL)
    {
        // Remove all occurrence of word from current line
        removeAll(buffer, toRemove);

        // Write to temp file
        fputs(buffer, fTemp);
    }


    /* Close all files to release resource */
    fclose(fPtr);
    fclose(fTemp);


    /* Delete original source file */
    remove(path);

    /* Rename temp file as original file */
    rename("delete.tmp", path);


    printf("\nAll occurrence of '%s' removed successfully.", toRemove);

    return 0;
}



/**
 * Remove all occurrences of a given word in string.
 */
void removeAll(char * str, const char * toRemove)
{
    int i, j, stringLen, toRemoveLen;
    int found;

    stringLen   = strlen(str);      // Length of string
    toRemoveLen = strlen(toRemove); // Length of word to remove


    for(i=0; i <= stringLen - toRemoveLen; i++)
    {
        /* Match word with string */
        found = 1;
        for(j=0; j < toRemoveLen; j++)
        {
            if(str[i + j] != toRemove[j])
            {
                found = 0;
                break;
            }
        }

        /* If it is not a word */
        if(str[i + j] != ' ' && str[i + j] != '\t' && str[i + j] != '\n' && str[i + j] != '\0') 
        {
            found = 0;
        }

        /*
         * If word is found then shift all characters to left
         * and decrement the string length
         */
        if(found == 1)
        {
            for(j=i; j <= stringLen - toRemoveLen; j++)
            {
                str[j] = str[j + toRemoveLen];
            }

            stringLen = stringLen - toRemoveLen;

            // We will match next occurrence of word from current index.
            i--;
        }
    }
}

Suppose contents of <strong>data/file4.txt</strong>

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

Output

Enter path of source file: data\file4.txt
Enter word to remove: is

All occurrence of 'is' removed successfully.

After removing contents of <strong>data/file4.txt</strong>

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

Also read

Happy coding 😉