Test for NULL pointer when freeing/closing:

[bert]

if (f) fclose(f);

if (p) free(p);

p = NULL;

[CatherineTower]

I can get a jump on this if you'd like.

[bert]

Hi CalvinTower,

Thank you for forking libdxf and making the above offer.

Hoping to see your pull requests soonish ;-)

Thanks in advance and with kind regards,

Bert Timmerman.

[CatherineTower]

A couple of questions just to make sure we're on the same page about this:

1. Do you want the test for a null pointer to be inside the freeing function or before entering the freeing function?

2. Do you want the freeing functions to set the pointer to NULL before returning?

And just a small heads-up, I'm still somewhat new to using Git and GitHub, so I apologize for any difficulties that may arise due to my inexperience.

I look forward to working with you on this project.
Calvin Tower

[bert]

Hi,

I'm not an expert on this, and I can't know on which OS-es the libdxf library will be compiled.

For some OS-es, freeing a NULL poniter is a noop (no operation), for others it might not be a noop, so it might be good to test up front.

If freeing a pointer leads to garbled content of the freed variable, I'd rather have \0 or NULL stored in that memory.

I hope this helps a bit to give direction ;-)

Kind regards,

Bert Timmerman.

[CatherineTower]

Absolutely it does, thank you very much. I'll get working on it and submit a pull request once I've got some code written.

[bert]

Thanks

[bert]

Stack overflow might help, as in :

https://stackoverflow.com/questions/6054271/freeing-pointers-from-inside-other-functions-in-c

[CatherineTower]

I'm sorry to be bothering you again, but I could use a bit more direction. I've been searching through the source code for an instance of the NULL-free problem and haven't found a place where it happens. Could you give me perhaps a hint on where to look for something like this?

Thank you,
Calvin Tower

[bert]

Hi Calvin,

There is a lot of these.

Example: 3dface.c line 748 reads:

free (face->linetype);

and before freeing that pointer to the linetype member t is not tested for containing NULL.

if (face->linetype)
{
free (face->linetype);
}
else
{
fprintf (stderr,
(_("Error in %s () a NULL pointer was found.\n")),
FUNCTION);
}

and based on the severity this is either a Warning or an Error.

Warnings can be handled by the code in libdxf by defaulting to a safe state (no crash),

Errors should terminate the operation or function without doing further damage.

It might be that creating a macro and invoking that can improve the effort to resolve this issue.

Kind regards,

Bert Timmerman.