Don't pay attention to my last article. It had a sintax mistake

Good Morning People!!

Actually,  i'm editing a C program on my UNIX system that
modifies the user's record. After making the modifications, the program
saves these ones in a new file (datos_usuarios2 - opened in "w" mode); the
source file is called "datos_usuarios", opened in "r" mode. The problem is
that when the program tries to writes the new data on "datos_usuarios" (the
source file) it failures!!! It doesn't record any data!! I mean, when i
make a "ls -la", appears the source file with 0 bytes!!!!

The program makes this as follows:

  system("mv datos_usuarios datos_usuarios.respaldo");

  if((from=fopen("datos_usuarios2", "r")) == NULL)
    {
      perror("datos_usuarios2"); exit(0);
    }
  if((to=fopen("datos_usuarios","w")) == NULL)
    {
      perror("datos_usuarios"); exit(0);
    }
  while((n=fread(buf, sizeof(char), BUFSIZ, from)) > 0)
    fwrite(buf, sizeof(char), n, to);
  fclose(from, to);

PLEASE, IF U HAVE ANY ANSWER E-MAIL ME (gmanzano@dino.conicit.ve) RIGHT NOW!

THANKS IN ADVANCE...  Greg!