1. One process runs another process

• Qt Of QProcess Class is used to start and communicate with an external program .
• Use start() Function to run a process , after QProcess Get into Starting state ;
• When the program has run ,QProcess Will enter Running Status and send started() The signal ;
• When the process exits ,QProcess Return to NoRunning Status and launch finished() The signal .

2. Routine code

• mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QProcess>

namespace Ui {
    
class MainWindow;
}

class MainWindow : public QMainWindow
{
    
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
    void on_pushButton_clicked();

    void showResult();
    void showState(QProcess::ProcessState state);
    void showError();
    void showFinished(int,QProcess::ExitStatus);

private:
    Ui::MainWindow *ui;

    QProcess myProcess;
};

#endif // MAINWINDOW_H

• mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include <QTextCodec>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    
    ui->setupUi(this);

    // Add signal and slot Association 
    connect(&myProcess,&QProcess::readyRead,this,&MainWindow::showResult);
    connect(&myProcess,&QProcess::stateChanged,this,&MainWindow::showState);
    connect(&myProcess,&QProcess::errorOccurred,this,&MainWindow::showError);
    connect(&myProcess,SIGNAL(finished(int,QProcess::ExitStatus)),
                              this,SLOT(showFinished(int,QProcess::ExitStatus)));
}

MainWindow::~MainWindow()
{
    
    delete ui;
}

void MainWindow::on_pushButton_clicked()
{
    
    // Start Notepad program , Because it's in Windows Under the system directory , The directory has been added to the system PATH In the environment variables , So you don't need to write a specific path 
    //myProcess.start("notepad.exe");

    QString program = "cmd.exe";
    QStringList arguments;
    arguments<<"/c dir&pause";
    myProcess.start(program,arguments);
}

void MainWindow::showResult()
{
    
    QTextCodec * codec = QTextCodec::codecForLocale();
    qDebug()<<"showResult: "<<endl<<codec->toUnicode(myProcess.readAll());
}

void MainWindow::showState(QProcess::ProcessState state)
{
    
    qDebug()<<"showState: ";
    if(state == QProcess::NotRunning)
    {
    
        qDebug()<<"No Running";
    }
    else if(state == QProcess::Starting)
    {
    
        qDebug()<<"Starting";
    }
    else
    {
    
        qDebug()<<"Running";
    }
}

void MainWindow::showError()
{
    
    qDebug()<<"showError:"<<endl<<myProcess.errorString();
}

void MainWindow::showFinished(int exitcode, QProcess::ExitStatus exitStatue)
{
    
    qDebug()<<"showFinished:"<<endl<<exitcode<<exitStatue;
}