/*
 * safe version of gets() function
 * returns one line from FILE* or NULL on case of EOF or out of memory
 */
char* sgets(FILE* f) {
 int bufsize = 10;  // initial size of buffer
 int gsize = 5;  // grow step
 char *buf;

 if (!(buf = malloc(bufsize))) {
  return NULL; // out of mem
 }

 char* ret = fgets(buf, bufsize, f);
 if (!ret) {
  return NULL; // EOF
 }
 while (strchr(buf, '\n') == 0) {
  bufsize += gsize;
  buf = realloc(buf, bufsize);
  if (!buf) {
   return NULL; // out of mem
  }
  char* p = buf + bufsize - gsize - 1; // pointer to prev str end ('\0')
  fgets(p, gsize + 1, f); // EOF impossible; +1 because of additional \0 from prev fgets
 }
 return buf;
}