Re: Division in loop

[Randi Botse <nightdecoder@gmail.com>]

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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