Qt QProcess get memory information

Question

I am trying to use QProcess to get the memory, I'm using RedHat 7.3, if I open a terminal and type free, this gives me:

            total        used        free      shared  buff/cache   available
Mem:        7865728     1602988     3984928      297040     2277812     5552268
Swap:       8126460           0     8126460

I've tried to produce the same in QT:

QProcess p;
p.start("free");
p.waitForFinished();
QString strMemory = p.readAllStandardOutput();
qDebug() << strMemory;
p.close();

However this doesn't work and my application hangs, I've also tried:

sh free

No better.

Just tried that, unfortunately its the same, application hangs when starting process. — SPlatten, Jul 03 '17 at 15:29
You may also want to put a time limit to `waitForFinished()` and check the status of the process. — drescherjm, Jul 03 '17 at 15:31
This may be a contributing factor, I was trying this whilst in the Qt IDE / Debugger, if I execute the application in a terminal outside of the IDE it works and I can see the output of free displayed in the console. — SPlatten, Jul 03 '17 at 15:44

score 0 · Answer 1 · answered Jul 03 '17 at 15:39

0

Try something like this:

const QString command { "free" };

QProcess p {};
p.start( command );
if ( !p.waitForFinished( -1 ) )
{
    qWarning() << "Error:" << p.readAllStandardError();
    return;
}

const auto& output = p.readAllStandardOutput();
qDebug() << "Output:" << output;

answered Jul 03 '17 at 15:39

Azeem

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That really isn't any different to my original code. – SPlatten Jul 03 '17 at 15:43
@SPlatten: Well, there are changes e.g. infinite timeout, check in case of error and printing the `stderr`. BTW, did you test it? – Azeem Jul 03 '17 at 15:47
I did test it as my new comment in my original post shows, yes, it works outside of the IDE, but not within, as does my original code. – SPlatten Jul 03 '17 at 15:47
@SPlatten: Strange! Never had an issue like that. – Azeem Jul 03 '17 at 15:51
It has to be something to do with the IDE, it works perfectly when run directly from the console. – SPlatten Jul 03 '17 at 15:51
@SPlatten: Yup. Seems like it. Please update your question if you find something about this issue. – Azeem Jul 03 '17 at 15:56
Yes, ok, no problem. – SPlatten Jul 03 '17 at 15:57

score 0 · Accepted Answer · answered Jul 12 '17 at 07:18

0

After much playing around I found that the starting the a child process works outside of the IDE but not from within it.

answered Jul 12 '17 at 07:18

SPlatten

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score -1 · Answer 3 · answered Jul 03 '17 at 16:07

-1

You are using the synchronous API wrong. try the asynch one:

QProcess p;
QString strMemory;
QObject::connect(&p,&QProcess::readyReadStandardOutput,[&strMemory,&p]()->void{strMemory += QString::fromLatin1(p.readAllStandardOutput());});
QObject::connect(&p,&QProcess::readyReadStandardError,[&strMemory,&p]()->void{strMemory += QString::fromLatin1(p.readAllStandardError());});
QObject::connect(&p,static_cast<void(QProcess::*)(int, QProcess::ExitStatus)>(&QProcess::finished),[&strMemory]()->void{qDebug() << strMemory;});
p.start("free");

answered Jul 03 '17 at 16:07

IlBeldus

1,040
6
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Having tried your proposed solution, the result is identical, it doesn't work from within the IDE and my original solution does the same, I suspect it will work outside of the IDE as does mine. – SPlatten Jul 04 '17 at 06:53
Another problem is that the scope of the object p will be destroyed before it completes unless 'p' is global or static. – SPlatten Jul 04 '17 at 07:20
@SPlatten lifecycle can be easily managed. just allocate on heap and connect finised signal to deleteLater slot. It's a trivial fix – IlBeldus Jul 04 '17 at 09:20
Still doesn't explain why it doesn't work in the IDE, I tried with: static QProcess p to get rid of the problem with it being destroyed. – SPlatten Jul 04 '17 at 09:23

Qt QProcess get memory information

3 Answers3