qt多线程共享内存怎么写

在Qt中，可以使用QSharedMemory类来实现多线程共享内存。下面是一个简单的示例代码，展示如何使用QSharedMemory类实现多线程共享内存：

#include <QtCore/QCoreApplication>
#include <QtCore/QSharedMemory>
#include <QtCore/QBuffer>
#include <QtCore/QDebug>
#include <QtCore/QThread>

class SharedMemoryWriter : public QThread
{
public:
    void run()
    {
        QSharedMemory sharedMemory("MySharedMemory");
        if (!sharedMemory.create(1024)) {
            qDebug() << "Unable to create shared memory segment.";
            return;
        }

        QBuffer buffer;
        buffer.open(QBuffer::ReadWrite);
        QDataStream out(&buffer);
        out << QString("Hello world!");

        int size = buffer.size();
        if (size > sharedMemory.size()) {
            qDebug() << "Unable to write to shared memory segment. Insufficient space.";
            return;
        }

        sharedMemory.lock();
        char *to = (char*)sharedMemory.data();
        const char *from = buffer.data().data();
        memcpy(to, from, qMin(size, sharedMemory.size()));
        sharedMemory.unlock();

        qDebug() << "Data written to shared memory segment.";
    }
};

class SharedMemoryReader : public QThread
{
public:
    void run()
    {
        QSharedMemory sharedMemory("MySharedMemory");
        if (!sharedMemory.attach()) {
            qDebug() << "Unable to attach to shared memory segment.";
            return;
        }

        QString message;
        QBuffer buffer;
        QDataStream in(&buffer);

        sharedMemory.lock();
        buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
        buffer.open(QBuffer::ReadWrite);
        in >> message;
        sharedMemory.unlock();

        qDebug() << "Data read from shared memory segment:" << message;
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    SharedMemoryWriter writer;
    SharedMemoryReader reader;

    writer.start();
    writer.wait();

    reader.start();
    reader.wait();

    return a.exec();
}

上面的代码创建了两个线程，一个用于写入数据到共享内存中，另一个用于从共享内存中读取数据。在写入数据时，我们首先创建一个QBuffer对象，并将数据写入到该对象中。然后，我们检查共享内存的大小是否足够，如果足够，我们就将数据复制到共享内存中。在读取数据时，我们首先使用QSharedMemory类的attach()函数连接到共享内存，然后将共享内存中的数据复制到QBuffer对象中，并从中读取数据。