Qt-interest Archive, October 2006
How does Stdin should be handled in a Qapplication ?
Message 1 in thread
Hi all,
I am setting up an IPC using stdin / stdout / stderr.
The doc of the QProcess is very clear.
But... I cannot figure out how the **child** process should handle stdin
events...
How does a Qt application handles its stdin ?
Is there a QProcess-like API for the **child** process ?
Or a specific QEvent ?
Is it in QApplication ? Elsewhere ?
These are quite silly question but... I did not find answer after browsing
the doc quite a long time...
Sorry, and thx for your quick answers to this quick question ;=)
Best-
Nicolas
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Message 2 in thread
Nicolas Castagne wrote:
> Hi all,
>
> I am setting up an IPC using stdin / stdout / stderr.
>
> The doc of the QProcess is very clear.
>
> But... I cannot figure out how the **child** process should handle stdin
> events...
>
>
> How does a Qt application handles its stdin ?
> Is there a QProcess-like API for the **child** process ?
> Or a specific QEvent ?
> Is it in QApplication ? Elsewhere ?
>
>
> These are quite silly question but... I did not find answer after browsing
> the doc quite a long time...
>
> Sorry, and thx for your quick answers to this quick question ;=)
stdin (and stdout and stderr, for that matter) have standard file
descriptors, and you can use them just like a file. Just open them with
that special descriptor (0 for stdin, 1 for stdout and 2 for stderr; but
they are defined in stdio.h as well) and you're done. A bit of googling
would have have provided you with the answer...
André
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[ signature omitted ]
Message 3 in thread
Thx much AndrÃ,
Well, I thought Qt could have offered a dedicated, ready to use mean for
reading stdin.
I've tried using a QFile opened on stdin, but without true sucess.
Problems I have are :
1/ the QFile for stdin in the **child** process never emits the signal
void readyRead();
How should I detetect that data have been writen to my process' stdin ?
For the moment, I use a QTimer and check regularly for available data...
Other problems are then :
2/ QFile::bytesAvailable() always returns 0, even though my **parent**
QProcess wrote bytes + end-of-line.
3/ Though, calling QFile::readData ( char * data, qint64 maxSize ) does read
the data writen by the **parent** process.
4/ but only once every two sent messages (both the last, and previous
messages are then read).
5/ etc.
So, my top questions are still :
What are the key points I should follow to set up a portable IPC using
stdin/stdout ?
Is it recommanded not to use stdin/stdout, but another IPC mean
(sockets...) ? Why ?
Indeed, the QProcess class is veryclear on the subject of stdin/stdout...
But the doc and qt-interest say nothing on what I should do on the **child**
process' side, while what should be done is clearly not evidence (cf.
various questions on qt-interest, and the problems I have myself).
Thx in advance,
Best-
Nicolas
Well, I consider
Andrà Somers wrote:
> Nicolas Castagne wrote:
>
>> Hi all,
>>
>> I am setting up an IPC using stdin / stdout / stderr.
>>
>> The doc of the QProcess is very clear.
>>
>> But... I cannot figure out how the **child** process should handle stdin
>> events...
>>
>>
>> How does a Qt application handles its stdin ?
>> Is there a QProcess-like API for the **child** process ?
>> Or a specific QEvent ?
>> Is it in QApplication ? Elsewhere ?
>>
>>
>> These are quite silly question but... I did not find answer after
>> browsing the doc quite a long time...
>>
>> Sorry, and thx for your quick answers to this quick question ;=)
>
> stdin (and stdout and stderr, for that matter) have standard file
> descriptors, and you can use them just like a file. Just open them with
> that special descriptor (0 for stdin, 1 for stdout and 2 for stderr; but
> they are defined in stdio.h as well) and you're done. A bit of googling
> would have have provided you with the answer...
>
> AndrÃ
>
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