argv = (const char **) memcpy (nptr, argv, i);
argv = (const char **) memcpy (nptr, argv, i * sizeof (const char *));
execlp (const char *file, const char *arg, ...){  size_t argv_max = 1024;  const char **argv = alloca (argv_max * sizeof (const char *));  unsigned int i;  va_list args;  argv[0] = arg;  va_start (args, arg);  i = 0;  while (argv[i++] != NULL)    {      if (i == argv_max)	{	  const char **nptr = alloca ((argv_max *= 2) * sizeof (const char *));#ifndef _STACK_GROWS_UP	  if ((char *) nptr + argv_max == (char *) argv)	    {	      /* Stack grows down.  */	      argv = (const char **) memcpy (nptr, argv, i);	      argv_max += i;	    }	  else#endif#ifndef _STACK_GROWS_DOWN	    if ((char *) argv + i == (char *) nptr)	    /* Stack grows up.  */	    argv_max += i;	  else#endif	    /* We have a hole in the stack.  */	    argv = (const char **) memcpy (nptr, argv, i);	}      argv[i] = va_arg (args, const char *);    }  va_end (args);  return execvp (file, (char *const *) argv);}