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Tuesday, 30 July 2013

C program to replace a word in a file

Write a C program to replace a word in a file.


  #include <stdio.h>
  #include <string.h>
  #define MAX 256

  int main() {
        FILE *fp1, *fp2;
        char word[MAX], fname[MAX];
        char string[MAX], replace[MAX];
        char temp[] = "temp.txt", *ptr1, *ptr2;

        /* get the input file from the user */
        printf("Enter your input file name:");
        fgets(fname, MAX, stdin);
        fname[strlen(fname) - 1] = '\0';

        /* get the word to delete from the user */
        printf("Enter the word to be replaced:");
        scanf("%s", word);

        /* get the word to replace */
        printf("Enter your replace word:");
        scanf("%s", replace);

        /* open input file in read mode */
        fp1 = fopen(fname, "r");

        /* error handling */
        if (!fp1) {
                printf("Unable to open the input file!!\n");
                return 0;
        }

        /* open temporary file in write mode */
        fp2 = fopen(temp, "w");

        /* error handling */
        if (!fp2) {
                printf("Unable to open temporary file!!\n");
                return 0;
        }

        /* delete the given word from the file */
        while (!feof(fp1)) {
                strcpy(string, "\0");
                /* read line by line from the input file */
                fgets(string, MAX, fp1);

                /*
                 * check whether the word to delete is
                 * present in the current scanned line
                 */
                if (strstr(string, word)) {
                        ptr2 = string;
                        while (ptr1 = strstr(ptr2, word)) {
                                /*
                                 * letters present before
                                 * before the word to be replaced
                                 */
                                while (ptr2 != ptr1) {
                                        fputc(*ptr2, fp2);
                                        ptr2++;
                                }
                                /* skip the word to be replaced */
                                ptr1 = ptr1 + strlen(word);
                                fprintf(fp2, "%s", replace);
                                ptr2 = ptr1;
                        }

                        /* characters present after the word to be replaced */
                        while (*ptr2 != '\0') {
                                fputc(*ptr2, fp2);
                                ptr2++;
                        }
                } else {
                        /*
                         * current scanned line doesn't 
                         * have the word that need to be replaced
                         */
                        fputs(string, fp2);
                }
        }

        /* close the opened files */
        fclose(fp1);
        fclose(fp2);

        /* remove the input file */
        remove(fname);
        /* rename temporary file name to input file name */
        rename(temp, fname);
        return 0;
  }



  Output:
  jp@jp-VirtualBox:~/$ cat data.txt 
  The moment You have realized God sitting 
  in the temple of every human body, the 
  moment You stand in reverence before every 
  human being and see God in him - that
  moment You am free from bondage,  everything that 
  binds vanishes, and You am free. 
  -Swami Vivekanada

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your input file name: data.txt
  Enter the word to be replaced: You
  Enter your replace word: I

  jp@jp-VirtualBox:~/$ cat data.txt 
  The moment I have realized God sitting 
  in the temple of every human body, the 
  moment I stand in reverence before every 
  human being and see God in him - that
  moment I am free from bondage,  everything that 
  binds vanishes, and I am free. 
  -Swami Vivekanada






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