How to get STDOUT from a QProcess?

Question

I thought I was going to get the output from a QProcess using the following code:

// Start the process
process.start(tr("php-cgi www/test.php"),QIODevice::ReadWrite);

// Wait for it to start
if(!process.waitForStarted())
    return 0;

// Continue reading the data until EOF reached
QByteArray data;

while(process.waitForReadyRead())
    data.append(process.readAll());

// Output the data
qDebug(data.data());
qDebug("Done!");

What I am expecting is to see the output from the program printed to the debug console, but all I see is:

Done!

I know that:

• The program is started fine, because the message at the end is printed.
• The program does print output because running the exact same command in the terminal produces a long string of text as expected.

What am I doing wrong here?

Solution 1

Before starting your process call:

process.setProcessChannelMode(QProcess::MergedChannels);

It will cause printing everything (even STDERR output) to STDOUT output.

Solution 2

Here is some clarification:

According to http://doc.qt.io/qt-5/qprocess.html#ProcessChannelMode-enum,

• QProcess::MergedChannels: QProcess merges the output of the running process into the standard output channel (stdout). The standard error channel (stderr) will not receive any data.[...]

but

• QProcess::ForwardedChannels: QProcess forwards the output of the running process onto the main process. Anything the child process writes to its standard output and standard error will be written to the standard output and standard error of the main process.

Comments

[Valentin H]

There is no point enclosing executable with language translation macro tr(). I also doubt, that putting executable and parameter as first argument would work. Better: process.start("php-cgi", QStringList()<<"www/test.php",QIODevice::ReadWrite);

[C--]

Processing the main process's output is slightly easier. So, thanks.