get error message from qprocess

user4592357

QProcess has error() method which returns an enum, and an exitCode() method which returns an int.
how can i get the actual message why e.g. startDetached() failed? maybe pass exitCode() to strerror()?

Christian Ehrlicher

Don't use startDetached() when you want to get the stdout/stderr messages. See http://doc.qt.io/qt-5/qprocess.html#startDetached
When a process is started with start() you can read stdout/stderr: http://doc.qt.io/qt-5/qprocess.html#readAllStandardError

user4592357

i don't want to write to std out/err, i want to print the error message in application, on some widget

SGaist

Hi,

What @Christian-Ehrlicher suggested is for your to be able to read the output generated by the application started using QProcess. What you do with said output is up to you.

user4592357

@SGaist
what about errorString()?

jsulm

@user4592357 said in get error message from qprocess:

what about errorString()?

There is no such thing. You can either connect a slot to http://doc.qt.io/qt-5/qlistwidget.html#selectedItems or call http://doc.qt.io/qt-5/qprocess.html#error. You will get an enum value (one of the http://doc.qt.io/qt-5/qprocess.html#ProcessError-enum), then you can do what ever you want with it. Like:

ProcessError error = process.error();
switch(error) {
case FailedToStart:
    ui->label->setText("Failed to start");
...
}

To get exit code call http://doc.qt.io/qt-5/qprocess.html#exitCode
It's all in the documentation.

user4592357

@jsulm
https://doc.qt.io/qt-5/qiodevice.html#errorString

jsulm

@user4592357 Oh, yes, forgot about inherited methods, you're right :-)
But keep in mind that this will not necessarily return errors specific to QProcess (like QProcess::Crashed) as QIODevice does not know anything about them. You still should use error() from QProcess also.

user4592357

@jsulm
should i do like this?

if (!process.start(path, args))
{
    auto err = process.error();
    switch (err)
    ...
}

or catch errorOccurred() signal?

i don't need specific handling for each type of error, i just need one string indicating the error.

jsulm

@user4592357 I would catch the signal as an error can occur after the process was successfully started.
If you only want to know whether the process was started then the first approach is easier.

user4592357

@jsulm
okay and i initially asked this: maybe pass exitCode() to strerror()? what about that?

jsulm

@user4592357 "maybe pass exitCode() to strerror()" - what do you mean by that? Do you mean stderror?

user4592357

@jsulm
no. http://man7.org/linux/man-pages/man3/strerror.3.html

jsulm

@user4592357 strerror is not about exit code but errors occurring during run time of the application. There is no standard for exit codes. The only thing which is usually a valid assumption is: 0 means "everything fine". Everything != 0 signals an issue. But what exactly an exit code means is up to the application.