如何从共享内存中读取和写入以创建数组QT

Question

我尝试了以下操作：

写入

int a[5]={1,2,3,4,5};
QBuffer buffer;
    buffer.open(QBuffer::ReadWrite);
    QDataStream out(&buffer);
    out << a[5];
    int size = buffer.size();
    if (!sharedMemory.create(size)) {
        ui.label->setText(tr("Unable to create shared memory segment."));
        return;
    }
    sharedMemory.lock();
    char *to = (char*)sharedMemory.data();
    const char *from = buffer.data().data();
    memcpy(to, from, qMin(sharedMemory.size(), size));
    sharedMemory.unlock();

读取

sharedMemory.attach();
QBuffer buffer;
    QDataStream in(&buffer);
    int a[5];
    //QImage image;
    QString fileName;
    int num;
    sharedMemory.lock();
    buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
    buffer.open(QBuffer::ReadOnly);
    in >> a[5];
    sharedMemory.unlock();

但我的想法是错误的。我不知道如何读写是一个由字符和整数组成的数组。

Answer 1

这里的第一个实际问题是a[5]：数组a只有5个项，因此第5个索引超出了它的边界。要写和读整个数组，您可以1）一次只写一项；或2）与诸如CCD_ 3的向量或列表对象。

1.作为阵列

写入：

int a[5]={1,2,3,4,5};
QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QDataStream out(&buffer);
//write item by item
for (int i=0; i<5; i++) {
    out << a[i];
}
int size = buffer.size();
if (!sharedMemory.create(size)) {
    cout << "Unable to create shared memory segment: "<<sharedMemory.errorString().toStdString()<<endl;
    return;
}
sharedMemory.lock();
char *to = (char*)sharedMemory.data();
const char *from = buffer.data().data();
memcpy(to, from, qMin(sharedMemory.size(), size));
sharedMemory.unlock();

阅读：

sharedMemory.attach();
QBuffer buffer;
QDataStream in(&buffer);
sharedMemory.lock();
buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
buffer.open(QBuffer::ReadOnly);
int len = sharedMemory.size()/sizeof(int);
int* a = new int[len];
for (int i=0; i< len; i++) {
    in >> a[i];
}
sharedMemory.unlock();
//delete a; 

（注意：使用后不要忘记删除a。）

2.作为QVector

写入：

QVector<int> vec;
vec << 1<<2<<3<<4<<5;
QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QDataStream out(&buffer);
//write the vector object
out << vec;
int size = buffer.size();
if (!sharedMemory.create(size)) {
    cout << "Unable to create shared memory segment: "<<sharedMemory.errorString().toStdString()<<endl;
    return;
}
sharedMemory.lock();
char *to = (char*)sharedMemory.data();
const char *from = buffer.data().data();
memcpy(to, from, qMin(sharedMemory.size(), size));
sharedMemory.unlock();

阅读：

sharedMemory.attach();
QBuffer buffer;
QDataStream in(&buffer);
sharedMemory.lock();
buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
buffer.open(QBuffer::ReadOnly);
QVector<int> vec;
in>>vec;
sharedMemory.unlock();