Re: Division in loop

[Eric Bambach <bot403@cisu.net>]

On Tuesday 08 September 2009 09:39:40 pm you wrote:
> Hi again...
>
> int fd; /* RS232 serial link */
> int fdp; /* file descriptor for a regular file */
> struct stat stat;
> size_t bytes = 0;
> void *buffer; /* buffer, will be allocated */
> ...
>    while (bytes < stat.st_size) {
>        ret = read(fdp, buffer + bytes, stat.st_size - bytes);
>        if (ret == -1) {
>            perror("read");
>            return -1;
>        }
>        ret = write(fd, buffer + bytes, ret);
>        if (ret == -1) {
>            perror("write");
>            return -1;
>        }
>        bytes += ret;
>        progress = (int) (bytes * 100) / stat.st_size;
>        printf("\rcompleted: %i%%", progress); /* NO OUTPUT, UNTIL LOOP
> ENDED */ fflush(stdout);
>    }
> ...
>
> Then i see printf() never output the message until the loop has ended...
> 'fdp' is a file descriptor to a local file, i send it through a serial
> connection (RS232),
> i use a serial connection so i can practice Linux's File I/O operation
> in real world ;p
>
> the receiver can output the progress's message, but the sender (the
> above code) could not...
> this is the receiver codes:
>
> ...
> while (bytes < size) {
>        ret = read(fd, buffer + bytes, size - bytes);
>        if (ret == -1) {
>            perror("read");
>            return -1;
>        }
>        ret = write(fdp, buffer + bytes, ret);
>        if (ret == -1) {
>            perror("write");
>            return -1;
>        }
>        bytes += ret;
>
>        progress = (int) (bytes * 100) / size;
>        printf("\rcompleted: %i%%", progress); /* HAS OUTPUT */
>        fflush(stdout);
>    }
> ...
>
> On Tue, Sep 8, 2009 at 8:49 PM, Glynn Clements<glynn@gclements.plus.com> 
wrote:
> > Tim Walberg wrote:
> >> Maybe you want "(bytes * 100) / size"?
> >
> > However, if int and size_t are 32-bit, that will overflow at around
> > 20 or 40 MB (20 for signed, 40 for unsigned), which isn't really all
> > that much. Converting to either double or long long might be wise,
> > i.e.
> >
> >        percent = (int)(bytes * 100.0) / size;
> > or:
> >        percent = (int)(bytes * 100LL) / size;
> >
> > --
> > Glynn Clements <glynn@gclements.plus.com>
>
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Wow. I feel silly. Ignore my previous message. It's late here and I missed the 
fflush().