Thread: SIGABRT upon free()

Hello all,

For some reason when I free(buffer) below, I always get a SIGABRT and I have no clue why.
Looking at the values buffer contains just before the free(), it has exactly what I'd expect,
just a few bytes worth of data, and num_bytes seems to have the correct amount. The original
malloc() returns a valid address, not NULL, so that seemed to work. Any ideas??

Code:

int ReceiveFeedback(comm_data_t* port, char *result, int *MPTR, int *timestamp)
{
   int       bytesReceivedSoFar = 0;  /* how many bytes we've read thus far */
   int       bufferSize = 1024;    /* size of buffer */
   int       select_value;         /* what select() returns */
   char      *buffer;              /* what we can grab from our port at each select iteration */
   char      *stringSoFar;         /* our total string built thus-far */
   int       num_bytes;            /* the number of bytes we read from our port */
   fd_set    watchset;             /* fd_set we want to watch for reading */
   struct timeval loopdelay;       /* str dictating how long select() should wait */
   int       junkInt;              /* garbage used to double-check sscanf */
   char      junkChar;             /* garbage used to double-check sscanf */
   const int bytesExpectedForSuccess = 40;  /* minimum bytes needed for success. stringSoFar value tested also */

   buffer = malloc (sizeof(char) * (2000));
   strcpy(buffer, "");

   stringSoFar = malloc (sizeof(char) * (30000));
   strcpy(stringSoFar, "");

   while (1)
   {
      strcpy(buffer, "");
      loopdelay.tv_sec = 5;  /* wait a long time before giving up */
      loopdelay.tv_usec = 0; /* must reset this for each call     */
      FD_ZERO(&watchset);    /* clear all bits in this set        */
      FD_SET(port->fd, &watchset);   /* watch our data instrument */

      /*  now keep reading data until we have our full menu */
      if ((select_value = select((port->fd)+1, &watchset, NULL, NULL, &loopdelay)) > 0)
      {
         /* all we're listening to is 1 port so no need for FD_ISSET */

         /* we got some data */
         num_bytes = read(port->fd, buffer, bufferSize);

	 if (num_bytes > 0)
	 {
	    /* we read something! */
	    /* take whatever we read this time and append it to what we've read over the past */
	    buffer[num_bytes] = 0x00;
            bytesReceivedSoFar += num_bytes;
	    strncat(stringSoFar, buffer, num_bytes);

	    /* does what we've read contain our substring? */
	    if (sscanf(stringSoFar, "%*[^A]A%i L+%i C%*c%*c%*c%c", &junkInt, MPTR, &junkChar) == 3)
	    {
	       /* we found our substring. see if there's enough data to send onward */
	       if (bytesReceivedSoFar < bytesExpectedForSuccess)
               {
	          /* we found the end of the CR10's response, but we know we didn't get any meaningful data */
                  strcpy(result, "");
		  free (buffer);
                  free (stringSoFar);
		  return (-1);
               } /* end if */

	       else
	       {
	          /* we found the end and we have enough bytes to have meaningful data */
	          strcpy(result, stringSoFar);
	          free (buffer); /* ------------------------- ALWAYS CAUSES SIGABRT on free()???? --- */
	          free (stringSoFar);
	          return (1);
	       } /* end else */

	    } /* end if sscanf == 3 */

	 } /* end if num_bytes > 0 */

      } /* end if select > 0 */

      else if (select_value == 0)
      {
         /* select returned 0, nothing more to ever read */
         strcpy(result, stringSoFar);
         free (buffer);
         free (stringSoFar);
         return (-2);
      } /* end else select == 0 */

      else
      {
         /* select returned negative value like EINTR so ignore */
	 ;
      } /* end else */

   } /* end while */

   /* we should never get here */
   strcpy(result, stringSoFar);
   free (buffer);
   free (stringSoFar);
   return (-3);

} /* end ReceiveFeedback(...) */

Thanks for any help.

Thanks for the great feedback. I'll give your suggestions a try and see if I can improve my code.