Using QProcess to read standard output

问题

In my QT widget application I am attempting to run a shellscript that opens a C++ program and provides inputs to the program as well. The program starts a command prompt that requires the users input to start. Once the program is started the output of the program is redirected via the standard output to a text file. I am attempting to use QProcess to open and run this shellscript, then read the standard output that is being used to print the result of the C++ program to the text file. The shell script only runs this process and does not terminate it. This is because I need to continuously read this output into the GUI as the program is running. It will not be sufficient to wait until the program is finished to read this information. I am fairly new to QT and C++ programming. I was hoping that someone could help me with my implementation of this.

QProcess process;
process.start("/home/pi/Desktop/ShellScripts/RunTutorial3.sh");
QString output =process.readAllStandardOutput();
qDebug() << output;
QString err = process.readAllStandardError();
qDebug() << err;

I have experimented with using other read function such as readline and also trying to start the process as a detatched process. I have not had success with any of my experimentations. Is it possible to do what I am attempting in QT. I just need the program to run continuously and for QT to read this output every so often.

Shell script:

#!/bin/bash
cd
cd Desktop
cd tutorial3App
cd bin
echo "start" | ./tutorial3

C++ code: I need the meanTOE value to be captured in standard output to use in my GUI.

/ Calculate average time to end of discharge
            double meanToE = std::accumulate(ToESamples.begin(), ToESamples.end(), 0.0)/ToESamples.size();
            file << ": EOL in " << meanToE << " s" << std::endl;

回答1:

As I said in my comments one of the main problems is that when you run tutorial3 that process is separated so you can not get the output. Therefore, I recommend executing it directly, and QProcess is probably a local variable, eliminating after printing an empty text, a possible solution is to create a pointer. Another improvement would be to use the readyReadStandardOutput and readyReadStandardError signals since the impressions are not automatic.

QProcess *process = new QProcess(this);

connect(process, &QProcess::readyReadStandardOutput, [process, this](){
    QString output =process->readAllStandardOutput();
    qDebug() << "output: "<< output;
});

connect(process, &QProcess::readyReadStandardError, [process](){
    QString err = process->readAllStandardError();
    qDebug() << "error: "<<err;
});

process->setWorkingDirectory("/home/pi/Desktop/tutorial3App/bin/")
process->start("tutorial3", QStringList() << "start");

回答2:

I think you have to read about signals and slots in Qt. QProcess has got a signal readyReadStandardOutput. So you have to connect to this signal and in your slot you should use QProcess function readAllStandardOutput. In other words when your shell programm outputs something you catch it in your slot and dump it or whatever you want.

Check the answer on this question. It might help you.

reading and writing to QProcess in Qt Console Application

来源：https://stackoverflow.com/questions/49058051/using-qprocess-to-read-standard-output

标签

c++

Linux

shell

qprocess