1 #include<stdio.h>
  2 #include<string.h>
  3 #include<stdlib.h>
  4 #include<stdbool.h>
  5 #include<errno.h>
  6
  7 extern int errno;
  8
  9 int main(int argc, char *argv[])
 10 {
 11         if(argc != 2) {
 12                 fprintf(stderr, "Invalid input\n");
 13                 exit(1);
 14         }
 15
 16         FILE* fp;
 17
 18         char *orig = "func";
 19         char *new = "printf";
 20         char *ch;
 21
 22         int i;
 23
 24         fp = fopen("code_to_change.c", "r+");
 25                 if(fp = NULL) {
 26                         fprintf(stderr, "Cannot open file\n");
 27                         exit(1);
 28                 }
 29                 else if(errno != 0) {
 30                         fprintf(stderr, "Unexpected error\n");
 31                         exit(1);
 32                 }
 33                 else {
 34                         return 0;
 35                 }
 36
 37         while((i = fgetc(fp)) != EOF) {
 38                 if(ch == orig) {
 39                         strcpy(orig, new);
 40                 }
 41         }
 42         fclose(fp);
 43
 44         return 0;
 45
 46 }