It might be because you've got that flush call commented out?
Sent from my iPad
On 2 Jul 2011, at 17:32, Dirk Koopman <d...@tobit.co.uk> wrote:
> Here is a bit of C code that is part of something much bigger.
>
> #include <stdio.h>
> #include <unistd.h>
>
> #define GIT_VERSION "1.23-dev"
> #define GIT_COUNT "73"
> #define GIT_ID "daa3ab8"
>
> #define VERSION "1.23"
>
> main()
> {
> printf("\nThingy version %s (%s-%s-%s) (built %s, %s)\n\n", VERSION,
> GIT_VERSION, GIT_COUNT, GIT_ID, __TIME__, __DATE__);
> // fflush(stdout);
> _exit(0);
> }
>
>
> If one compiles it (cc vtest.c -o vtest) and runs it at a shell prompt, one
> gets:
>
> jim@mike2:~/thingy$ vtest
>
> Thingy version 1.23 (1.23-dev-73-daa3ab8) (built 16:21:49, Jun 30 2011)
>
> jim@mike2:~/thingy$
>
> All is well and seemingly as expected. However now do this:
>
> jim@mike2:~/thingy$ vtest | grep version
> jim@mike2:~/thingy$
>
> Stdout appears not to have been have been flushed. Which, after reading the
> man page for _exit is fair enough as it says: "The function _exit()
> terminates the calling process "immediately". Any open file descriptors
> belonging to the process are closed". This is, in fact, what is wanted in the
> larger program. This behaviour has only come to light, after several years
> mind, because some (other) poor fool wanted to grab the version no for some
> shell script or other, instead of just checking what a user had installed via
> a shell prompt.
>
> The fix is simply to fflush(stdout), before _exit().
>
> But how come I get output at a shell prompt, and not down a pipe (or a
> redirection either)? What special magic is occurring here?
>
> Dirk
>
>
>
>
