experiment3.c

   1 #include <stdio.h>
   2
   3 int main() {
   4     FILE *fd;
   5     char mac[13];
   6     unsigned long int counter = 0;
   7
   8     if ((fd = fopen("/tmp/maccounter", "r")) != NULL) {
   9         fread(mac, 12, sizeof(char), fd);
  10         mac[13] = '\0';
  11         counter = strtoul(mac, NULL, 16);
  12         counter++;
  13         fclose(fd);
  14     }
  15
  16     snprintf(mac, 13, "%012X\n", counter);
  17     if ((fd = fopen("/tmp/maccounter", "w")) != NULL) {
  18         fwrite(mac, 12, sizeof(char), fd);
  19         fclose(fd);
  20     }
  21 }