Computer Aided Design : 14526


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Subject:	Re: how does a line ends?
Newsgroups:	lugnet.cad
Date:	Sat, 7 Apr 2007 21:55:11 GMT
Viewed:	1757 times

In lugnet.cad, Travis Cobbs wrote:

OK, as promised, here it my fgets replacement:

That was quick! Thanks for taking the time to indulge me...

char *myFgets(char *buf, int bufSize, FILE *file)
{
    int i;

    for (i = 0; i < bufSize - 1; i++)
    {
        int char1 = fgetc(file);

        if (feof(file))
        {
            buf[i] = 0;
            if (i > 0)
            {
                return buf;
            }
            else
            {
                return NULL;
            }
        }
        if (char1 == '\r' || char1 == '\n')
        {
            int char2 = fgetc(file);

            buf[i] = '\n';
            buf[i + 1] = 0;
            if (!feof(file))
            {
                if (!(char1 == '\r' && char2 == '\n' ||
                    char1 == '\n' && char2 == '\r'))
                {
                    ungetc(char2, file);
                }
            }
            return buf;
        }
        buf[i] = (char)char1;
    }
    buf[bufSize - 1] = 0;
    return buf;
}

It seems to work, but I’m not 100% confident in its lack of bugs. Timing with 8464.mpd results in about 550ms for loading using fgets and 750ms using myFgets from above. On the one hand, thats a 50% slowdown based purely on that one change. On the other hand, 750ms isn’t very long, and while 8464.mpd isn’t exactly a huge file, it’s big enough to prove your point that the performance is fine.

It is interesting that it was that much time difference. Are these the total load times, or just profiling of the time spent inside the fgets() routines? I see one or two things you might tighten up in this code, but nothing that’s going to make it 50% faster.

I do wonder how this code compares to the stdlib fgets() implementation that you are using. Did you modify the original fgets, or did you write this one from scratch? Any chance you could post the original fgets code for comparison?

At this point, I’m much more concerned about any possible bugs in the code, though. I have a fairly high confidence level that fgets does what it’s supposed to do in all possible cases. I don’t have the same confidence level for the myFgets function above.

This code seems to work for me, and passes a quick visual read-through, but I know how you feel.

Message has 2 Replies:

		Re: how does a line ends?
(...) I timed the file reading/parsing portion of the model load. It would have been more difficult to time the actual amount of time spent inside fgets/myFgets, so realistically it's likely that myFgets is even slower in comparison to fgets. The (...) (18 years ago, 7-Apr-07, to lugnet.cad, FTX)

		Re: how does a line ends?
(...) Quick question. I was in a hurry, and wanted to play it safe, so I call feof instead of checking to see if char1 == EOF. Any idea what gets returned for extended ASCII characters (>= 128)? Does the int contain positive numbers greater than (...) (18 years ago, 7-Apr-07, to lugnet.cad, FTX)

Message is in Reply To:

		Re: how does a line ends?
(...) OK, as promised, here it my fgets replacement: char myFgets(char buf, int bufSize, FILE *file) int i; for (i = 0; i < bufSize - 1; i++) int char1 = fgetc(file); if (feof(file)) bufi = 0; if (i > 0) return buf; else return NULL; if (char1 == (...) (18 years ago, 7-Apr-07, to lugnet.cad, FTX)

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