Should I fclose(file) if an error occured?

Question

Code:

FILE *fp = fopen(filename, "r");
if (!fp)
{
    fprintf(stderr, "Failed to open a file\n");
    // fclose(fp) <-- should I close file here?
    exit(1);
}
// Some operations on the file.
fclose(fp);

Question:

If fopen() fails to open a file, should I still call fclose()?

Sourav Ghosh · Accepted Answer · 2015-05-29T16:29:30.850

5

No, you don't need to call fclose() inside if block. Once fopen() fails, it retruns NULL which need not be closed.

To elaborate, if fopen() is success, it will return a FILE *. That needs to be closed. FWIW, the returned pointer in this case, be of whatever value, gurantees to compare unequal with a NULL. In other words, if fopen() is a success, the returned pointer will always FAIL the if(!fp) check.

In error scenario (when the file cannot be opned for some reason), NULL will be retrurned. A NULL return value means, the file was not opened. You don't close what is not already opened. Simple.

edited May 29 '15 at 16:29

answered May 29 '15 at 16:15

Sourav Ghosh

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I knew that `fopen()` returns NULL but I wasn't sure if file was opened or not. Thanks! – Mateusz Piotrowski May 29 '15 at 16:17
2

I would say even clearer: since on error null is returned, you have nothing to close. – Sami Kuhmonen May 29 '15 at 16:21
1

A hanging issue: is it OK to call `fclose(NULL)`? I think it is, yet see no spec to back up. (Note:2 "retrun"s in answer) – chux - Reinstate Monica May 29 '15 at 16:33
I've just tested `fclose(NULL)`. Nothing special happened. – Mateusz Piotrowski May 29 '15 at 16:49

Should I fclose(file) if an error occured?

Code:

Question:

1 Answers1