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From: FangQ on 8 Dec 2009 10:37
hi

I have encountered a strange problem. I am writing a pascal (Lazarus)
GUI program to communicate with a C++ command line tool. In the C++
tool, it prints out various informations (with fprintf(stdout, ....) )
during the execution, and I was trying to capture it in the GUI.

Strangely, I found that my GUI only print the entire output at the end
of the execution. However, if I change the command to a shell command,
such as "du /usr/ --max-depth=1", or even the following script:

#!/bin/sh
echo $@
sleep 1
echo step 1 complete
sleep 1
echo step 2 complete
sleep 1
echo mcx complete

the intermediate output will be captured instantly during the
execution.

I am wondering if I need to manually flush the pipe in my C++ code?
and how to do that?

thanks

Qianqian
From: Barry Margolin on 8 Dec 2009 15:42
In article
<5d1467f9-9087-4ddd-8ad9-2e40d46a2fa6(a)e20g2000vbb.googlegroups.com>,
FangQ <fangqq(a)gmail.com> wrote:

> hi
>
> I have encountered a strange problem. I am writing a pascal (Lazarus)
> GUI program to communicate with a C++ command line tool. In the C++
> tool, it prints out various informations (with fprintf(stdout, ....) )
> during the execution, and I was trying to capture it in the GUI.
>
> Strangely, I found that my GUI only print the entire output at the end
> of the execution. However, if I change the command to a shell command,
> such as "du /usr/ --max-depth=1", or even the following script:
>
> #!/bin/sh
> echo $@
> sleep 1
> echo step 1 complete
> sleep 1
> echo step 2 complete
> sleep 1
> echo mcx complete
>
> the intermediate output will be captured instantly during the
> execution.

Programs flush their output when they exit, if not before, and shell
scripts flush their stdout after each built-in command.

>
> I am wondering if I need to manually flush the pipe in my C++ code?
> and how to do that?

Call fflush().

--
Barry Margolin, barmar(a)alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
From: FangQ on 8 Dec 2009 22:53
On Dec 8, 3:42 pm, Barry Margolin <bar...(a)alum.mit.edu> wrote:
> Call fflush().

that works! I should have known this. thank you very much
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