Is this an efficient use of QProcess?

[aha_1980]

@graniteDev yeah, should work.

just leave out the subsequent new lines.

@Lifetime-Qt-Champion well spotted , didn't see the leak...

[SGaist]

I didn't realise... You are using execute which is a static method that runs the commands and waits for it to finish. Thus you are currently creating QProcess objects for nothing.

[graniteDev]

@SGaist please explain?

[SGaist]

Static methods are not attached to an object, you should even have a compile warning telling you that you are calling a static method on an instance. See here for more details.

[JonB]

@SGaist said in Is this an efficient use of QProcess?:

I didn't realise... You are using execute which is a static method that runs the commands and waits for it to finish. Thus you are currently creating QProcess objects for nothing.

In which case, how come his process->waitForFinish(); even returns/doesn't error, because as you say the instance has never been start()ed?

[SGaist]

waitForFinished has a timeout with a default value but in this case, since the process is not even running it will return early.

[graniteDev]

I wonder if the confusion is that I left out the beginning code, the first process starts out:

QProcess *process = new QProcess(this);
process->execute(file1,args1);
process->waitforFinish();
process->close();

process = new QProcess(this);
process->execute(file2,args2);
process->waitforFinish();
process->close();

process = new QProcess(this);
process->execute(file3,args3);
process->waitforFinish();
process->close();

I get no compile errors, and it's working. Per the Qt documentation close() deletes the object, so I don't believe I'm creating a memory leak with what I'm doing.

However, if I can eliminate creating a new object and then deleting it every time, I'm for improving the code.

[JonB]

@SGaist
Ah, OK, I thought it might error "process not yet started".

[SGaist]

@graniteDev Warning doesn't mean error unless you enabled "all warning be errors" for your compiler. As for close, it doesn't delete anything. It will kill the process that you started and close the communication channels. It's unrelated to memory management.

@JonB waitForFinished will return false because of that.

[graniteDev]

@SGaist Ok, how should I go about this properly then? Could you provide some example code?

[SGaist]

QProcess::execute(file1, args1);

[graniteDev]

@SGaist I could run these from a static function? How then do I know when they are finished if there is no object to emit the signal?

[SGaist]

Did you read the documentation of the function ? execute runs the command and waits for it to finish. The returned value indicates what happened.

[graniteDev]

@SGaist yes but if i just run QProcess::execute(file1, args1); there is no object there for me to deal with.

[SGaist]

What do you want to deal with ? In the code you shown until now, what you are doing with your QProcess objects is already done "internally" by execute.

[graniteDev]

@SGaist never mind, I misunderstood because I'm not used to dealing with these. I was concerned that the subsequent processes could be started before the previous one finished, however execute is not asynchronous like start() is if I understood the documentation correctly.

[SGaist]

It is indeed not asynchronous.

[graniteDev]

@SGaist ok well thankyou, I will give this a try.

[graniteDev]

@SGaist Worked. Wow is that much much simpler.

If I may though, for my future reference, if I needed to actually use a QProcess *process = new QProcess(this); to run multiple things, how would I go about it?

[SGaist]

If in a fashion similar to execute see the Synchronous Process API in QProcess's documentation.