Add null check before closing file pointer

[hgqxjj]

Please review this change. Thanks!

Description:

Avoid calling fclose() with a NULL file pointer.

fopen() may fail and return NULL, so check ip before calling fclose(ip).

[jbowler]

Why?

[hgqxjj]

Hi @jbowler, Because fopen() may fail and return NULL. In that case, calling fclose(ip) would effectively call fclose(NULL), which is undefined behavior and may cause a crash. The ip != NULL check ensures we only close a successfully opened file.

[jbowler]

Your pull request says:

No description provided.

That's why I asked, "Why?"

[hgqxjj]

Thanks, I misunderstood your question. I've added the rationale to the PR description.

[jbowler]

Reasonable; the prior code would give a user who passed in a bogus file name a nasty rejoinder and stop listening to what he said (the failure is in a loop over the arguments).

Neither is satisfactory of course but the suggested change is reasonable.

[hgqxjj]

Thanks for the review and for the feedback!