Re: [ts-7000] malloc()

[Jason Stahls <>]

Ok, I had this working for a while then started mucking and broke it again.  Question is, why are you casting the returns to char *, I've always understood that a pointer is a pointer, it has no type, am I wrong?

Jason

Joe Bouchard wrote:

Now, a co-worker has raised a question about if this is a result of me 
misusing strtok_r(), I think I'm using it correctly but not sure.
    

Yeah, I can see a couple of issues.  I'm surprised you aren't getting segfaults.

When using both strtok and strtok_r it's a 2 step process.  Typically the first
call is before the loop, and subsequant calls are inside a loop.
char * p = strtok(char * s, char * delimiters);
       p = strtok(NULL, delimiters);
In the first call you give it the real "s", and after that, you give it NULL.
No it doesn't make sense. I didn't write it, but that's how it works.  And
remember that it destroys your original string, so if you need to keep it for
another use, you need to make a copy (which you were doing).

The thread safe version is strtok_r, and it's similar, except you need to
allocate another buffer, and pass that as the last parameter.

Here is a working example:

int main(void)
{
  char msg[] = "SEE:SPOT:RUN";
  char msg2[]= "RUN:SPOT:RUN";
  char * place_keeper = (char*)malloc(1024);

  // strtok uses only the original string and a spare pointer.
  // it looks like this the first time with strtok
  char * p = (char *) strtok(msg, ":");
  if (p)
    printf("Command=%s\n",p);

  while(p)
    {
      // it passes NULL on subsequent calls
      p = (char*)strtok(NULL, ":");
      if (p)
	printf("Command=%s\n",p);
    }

  printf("------------------------------------------\n");

  // strtok_r uses the original string,
  // and a spare pointer, and another buffer
  // it looks like this the first time with strtok_r
  p = (char*) strtok_r(msg2, ":", place_keeper);
  if (p)
    printf("Command=%s\n",p);

  while(p)
    {
      // it passes nulls on subsequant calls.
      p = (char*)strtok_r(NULL, ":", place_keeper);
      if (p)
	printf("Command=%s\n",p);
    }

  free(place_keeper);
  return 0;
}

Here is the result.
Command=SEE
Command=SPOT
Command=RUN
------------------------------------------
Command=RUN
Command=SPOT
Command=RUN


 
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