Checking for success of fwrite in C, perror

Question

With fwrite returning the number of successful elements written to the file, by saying:

if (!(fwrite(...))) {
    fprintf(stderr, "Failure");
    //perror(???)  I sometimes see code that says perror here and I don't know 
    //exactly what this does.
}

Does this check for successful writing to the file? Are there other things to worry about?

Thanks.

Answer 1

You can also use explain_fwrite(), explain_errno_fwrite, ... from libexplain.

The man page explains:

The explain_fwrite function is used to obtain an explanation of an error returned by the fwrite(3) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The errno global variable will be used to obtain the error value to be decoded.

This function is intended to be used in a fashion similar to the following example (the man-page was wrong here, as correctly pointed out by @puchu in the comment below. I corrected the code to address the issue):

if (fwrite(ptr, size, nmemb, fp) < nmemb)
{
    fprintf(stderr, "%s\n", explain_fwrite(ptr, size, nmemb, fp));
    exit(EXIT_FAILURE);
}

Caveat: This method is not thread-safe.