如何在C ++或Qt中创建进程？

Question

hello people a need your help, can be with qt or c++, i want to create a process BUT a process that use a function of my program not an external program, something like this .... sorry for the example and forgive my english thanks

void count(){blablabla}
int main(){QProcess p = new QProcess(count());p.start();}

Answer 1

IMHO, the easiest way would be to use threads. If your only objection to using thread is that the thread will be terminate, you can overcome it by waiting for the thread to finish before exiting the process.

void doSomething();

int main (int argc, char *argv[])
{
    QApplication app(argc, argv);
    ...
    // Start a doSomething() in another thread using pure C++11
    std::thread cppThread(&doSomething);
    // The same using Qt
    QFuture<void> qtThreadResult = QtConcurrent::run(&doSomething);
    ...
    int r = app.exec();
    ...
    // The Qt application is closed
    // We wait for the thread to complete
    cppThread.join();
    // The same using Qt
    qtThreadResult.waitForFinished();

    // Everything is finished, we can exit
    return r;
}

---

If you absolutely need to create another process you have 2 solutions, either you create 2 programs A and B, and you start B from A, or you have a single program and you need to provide a command line argument so it can change its behavior.

void doSomething();

int main (int argc, char *argv[])
{
    QApplication app(argc, argv);
    if (app.arguments().contains("--foo"))
    {
        doSomething();
        return 0;
    }
    else
    {
        return app.exec();
    }
}

You can then start the new process using Qt:

QProcess::startDetached("B");
QProcess::startDetached("A --foo");
QProcess::startDetached(QCoreApplication::applicationFilePath(), QStringList{"--foo"});

Using pure C++ it gets a little more complicated. You have system() on all platforms but it does not offer a lot of option if you need to manipulate the created process. Then you have platform specific solutions like execl() (& co.) on Linux and CreateProcess() on Windows.

Also note that this can get even more complicated if you need to share data between the 2 processes ; you will need to play with shared memories or sockets or pipes or stdin/stdout...

Answer 2

You can use QTimer. This will emit the timeout() signal at constant intervals. Example for one second timer,

QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(count()));
    timer->start(1000);

From then on, the count() slot is called every second. QTimer

Answer 3

I've done this via QtConcurrent as follow:

1) declare the method, which should run on an own thread:

void TestClass::startWorkerThread(int parameter1) {
    // do something
}

2) Start the method in a thread:

#include <QtConcurrent/QtConcurrent>
... 
QFuture<void> pFuture1 = QtConcurrent::run(this, &TestClass::startWorkerThread, parameter1);