QT笔记——QProcess学习

我们常常想通过某一个类，来启动一个外部进程

本文将讲解如何通过QProcess来进行启动外部进程

一：了解QProcess

QProcess是Qt框架提供的一个类，用于在应用程序中执行外部进程。它提供了一系列函数来启动、控制和与外部进程进行交互

1.启动进程的方式：
(1.1)分离式:外部程序启动程序后，主程序退出时，被调用的进程继续执行，不退出
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[static] bool QProcess::startDetached(const QString &program, const QStringList &arguments, const QString &workingDirectory = QString(), qint64 *pid = nullptr)

(1.2)一体式：当主程序退出时,被主程序调用起来的进程也退出

start还有其他的重载的函数，下面是其中一个
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void QProcess::start(const QString &program, const QStringList &arguments, QIODevice::OpenMode mode = ReadWrite)

2：常用的阻塞函数

// 主进程阻塞，直到外部程序启动完毕,
waitForStarted()// 主进程阻塞，直到外部程序执行完毕
waitForFinished()

3:被调用进程接受数据

4:主进程接受被调用进程的数据
(4.1)使用QFile输出内容被主进程捕获

QFile file;
file.open(1, QFile::WriteOnly);
file.write("finished");
file.close();

(4.2)使用输出流被主进程捕获

 cout << "it's message" << endl;

5：常用的信号
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//启动完毕
connect(process, &QProcess::started, this, [=]()
{});//捕获到消息时
connect(process, &QProcess::readyReadStandardOutput, this, [=]()
{});//完成
connect(process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, [=](int exitCode, QProcess::ExitStatus exitStatus)
{});//状态改变
connect(process, &QProcess::stateChanged, this, [=](QProcess::ProcessState state)
{});

二：使用QPrecess

1：startDetached 启动进程

1：使用了startDetached来启动进程，信号都是无效的，接受不到任何消息
2：当主进程关闭时，被调用的QTcpClientTest.exe 是不会退出的
3：主进程发送的参数，被调用的QTcpClientTest.exe 依然可以接受

void QTcpSeverTest::on_btn1_clicked()
{QProcess* process = new QProcess(this);QString str = QApplication::applicationDirPath() + "/QTcpClientTest.exe";QStringList list;list.append("123");list.append("456");//分离式 启动外部进程process->startDetached(str, list);//无效connect(process, &QProcess::started, this, [=](){qDebug() << "started";});//无效connect(process, &QProcess::readyReadStandardOutput, this, [=](){QString qstr(process->readAllStandardOutput());qDebug() << "startDetached:" << qstr;});connect(process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, [=](int exitCode, QProcess::ExitStatus exitStatus){QString result = process->readAll();qDebug() << "result:" << result;});//无效connect(process, &QProcess::stateChanged, this, [=](QProcess::ProcessState state){qDebug() << "show state:";switch (state){case QProcess::NotRunning:qDebug() << "Not Running";break;case QProcess::Starting:qDebug() << "Starting";break;case QProcess::Running:qDebug() << "Running";break;default:qDebug() << "otherState";break;}});}

2：start启动进程

1：使用了startDetached来启动进程，信号都是可以接受的
2：当主进程关闭时，被调用的QTcpClientTest.exe 是随着主进程一起退出
3：主进程发送的参数，被调用的QTcpClientTest.exe 可以接受参数

	QProcess* process = new QProcess(this);QString str = QApplication::applicationDirPath() + "/QTcpClientTest.exe";QStringList list;list.append("bbbbb");list.append("aaaaa");//启动完毕connect(process, &QProcess::started, this, [=](){qDebug() << "started:" ;});//捕获到消息时connect(process, &QProcess::readyReadStandardOutput, this, [=](){QString qstr(process->readAllStandardOutput());qDebug() << "readyReadStandardOutput:" << qstr;});//完成connect(process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, [=](int exitCode, QProcess::ExitStatus exitStatus){if (exitStatus == QProcess::NormalExit) {qDebug() << "Process finished with exit code:" << exitCode;}else {qDebug() << "Process crashed!";}});//状态改变connect(process, &QProcess::stateChanged, this, [=](QProcess::ProcessState state){qDebug() << "show state:";switch (state){case QProcess::NotRunning:qDebug() << "Not Running";break;case QProcess::Starting:qDebug() << "Starting";break;case QProcess::Running:qDebug() << "Running";break;default:qDebug() << "otherState";break;}});//一体式  启动外部进程process->start(str, list);

3：execute()启动进程

1：使用了execute来启动进程，信号是无效的
2：主进程一直处于阻塞状态，等待被调用的QTcpClientTest.exe完成(关闭软件)

	QProcess* process = new QProcess(this);QString str = QApplication::applicationDirPath() + "/QTcpClientTest.exe";QStringList list;list.append("bbbbb");list.append("aaaaa");//无效connect(process, &QProcess::started, this, [=](){qDebug() << "started:";});//无效connect(process, &QProcess::readyReadStandardOutput, this, [=](){QString qstr(process->readAllStandardOutput());qDebug() << "readyReadStandardOutput:" << qstr;});//无效connect(process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, [=](int exitCode, QProcess::ExitStatus exitStatus){QString result = process->readAll();qDebug() << "result:" << result;});//无效connect(process, &QProcess::stateChanged, this, [=](QProcess::ProcessState state){qDebug() << "show state:";switch (state){case QProcess::NotRunning:qDebug() << "Not Running";break;case QProcess::Starting:qDebug() << "Starting";break;case QProcess::Running:qDebug() << "Running";break;default:qDebug() << "otherState";break;}});//如果进程 QTcpClientTest 不关闭 或者完成 ， 则此进程一直卡住int exitCode = QProcess::execute(str, list);if (exitCode != 0) {qDebug() << "外部程序执行失败";}//接受进程捕获到输出的消息QByteArray output = process->readAllStandardOutput();QString msg = QString::fromLocal8Bit(output);qDebug() << msg;

打印的信息为：QIODevice::read (QProcess): device not open，说明execute没有打开设备，接受不到消息

4：start() + waitForFinished()启动进程

1：使用了execute来启动进程，信号是无效的
2：主进程一直处于阻塞状态，等待被调用的QTcpClientTest.exe完成(关闭软件)

	QProcess* process = new QProcess(this);QString str = QApplication::applicationDirPath() + "/QTcpClientTest.exe";QStringList list;list.append("bbbbb");list.append("aaaaa");//启动进程process->start(str,list);// 等待进程完成process->waitForFinished();//接受进程捕获到输出的消息QByteArray output = process->readAllStandardOutput();QString msg = QString::fromLocal8Bit(output);qDebug() << msg;