Qt主要是通过QSharedMemory类来访问以及操作共享内存。
以下是几个主要的步骤
1.对于QsharedMemory类的对象进行创建
利用QSharedMemory类创建实例对象时，必须为该共享内存指定关键字(即为该共享内存起一个名字)。只有当共享内存被设置了关键字之后，才可以执行创建create()、关联attach()等操作。为共享内存指定关键字有两种方法：
a.直接在通过构造函数来进行关键字设置：
比如：
QSharedMemory sendsharedMem;
QSharedMemory recvsharedMem;
MainWidget::MainWidget(QWidget *parent) :
QWidget(parent),sendsharedMem("SHAREFILE"),recvsharedMem("SHAREFILE")直接这样设置key
b. 对象构造好之后利用setKey来进行设置
比如：
sendsharedMem.setKey("SHAREFILE");
recvsharedMem.setKey("SHAREFILE");这样来设置
2、创建共享内存
QSharedMemory::ReadOnly 只读方式访问共享内存
QSharedMemory::ReadWrite 读写方式访问共享内存
3、关联共享内存
bool QSharedMemory::attach ( AccessMode mode =ReadWrite )
4、分离共享内存
bool QSharedMemory::detach ()
5、判断共享内存的关联状态
bool QSharedMemory::isAttached ()const
void QSharedMemory::setKey (const QString & key ) //设定共享内存关键字
6、锁定/解锁共享内存
bool QSharedMemory::lock () //锁定共享内存
bool QSharedMemory::unlock () //解锁共享内存
界面是这样，open用来打开本地图片并在左边label显示，save用来存储进共享空间，show用来读取共享空间的图在右边label显示，exit是退出
- //首先是打开本地图片并显示
- void Widget::InsertImage()
- {
- ui->btn_1 = qobject_cast<QPushButton*>(sender());
- QString fileName = QFileDialog::getOpenFileName( this,
- tr("打开文件"),
- "C:/Users/Administrator/Desktop",
- tr("任何文件(*.*)"
- ";;文本文件(*.txt)"
- ";;XML文件(*.xml)"
- ";;Images (*.png *.xpm *.jpg)"));
- QMovie *move=new QMovie(fileName);
- ui->lbl_1->setMovie(move);
- move->start();
- }
- //然后是存储共享空间
- void Widget::loadfromsharedMem()
- {
- sharedMemory.setKey("QSharedMemoryExample");<span style="white-space:pre"> </span>// 设置访问标识
- if (sharedMemory.isAttached())<span style="white-space:pre"> </span>//判断是否连接到共享块
- {
- // 将该进程与共享内存段分离
- if (!sharedMemory.detach())
- qDebug() << "Unable to detach from shared memory.";
- }
- QString fileName = QFileDialog::getOpenFileName(0, tr("打开文件"),
- "C:/Users/Administrator/Desktop",
- tr("Images (*.png *.xpm *.jpg)"));
- QImage image;
- if (!image.load(fileName))
- {
- qDebug() << "Selected file is not an image, please select another.";
- return;
- }
- // 将数据加载到共享内存中
- QBuffer buffer; <span style="white-space:pre"> </span>//将字符串转换为字节的介质
- buffer.open(QBuffer::ReadWrite);<span style="white-space:pre"> </span>//设置读取模式
- QDataStream out(&buffer);<span style="white-space:pre"> </span>//数据流
- out << image;
- int size = buffer.size();<span style="white-space:pre"> </span>//获得字节大小
- // 创建共享内存段
- if (!sharedMemory.create(size))<span style="white-space:pre"> </span>//检测共享内存是否创建成功
- {
- qDebug() << sharedMemory.errorString() << "\n Unable to create shared memory segment.";
- return;
- }
- sharedMemory.lock();<span style="white-space:pre"> </span>//锁定共享内存
- char *to = (char*)sharedMemory.data();<span style="white-space:pre"> </span>//共享内存的数据
- const char *from = buffer.data().data();<span style="white-space:pre"> </span>//被共享内存的数据
- memcpy(to, from, qMin(sharedMemory.size(), size));<span style="white-space:pre"> </span>//将要共享的内存copy到被共享的内存
- sharedMemory.unlock();
- }
- <span style="font-family:Arial;"><span style="line-height: 26px;">//接下来是读取
- void Widget::loadFromMemory()
- {
- receiveMemory.setKey("QSharedMemoryExample");<span style="white-space:pre"> </span>//声明共享内存的密钥
- // 将共享内存与该进程绑定
- if (!receiveMemory.attach())
- {
- ui->lbl_2->setText("Unable to attach from shared memory.");
- return;
- }
- // 从共享内存中读取数据
- QBuffer buffer;<span style="white-space:pre"> </span>//声明缓冲区
- QDataStream in(&buffer)<span style="white-space:pre"> </span>//声明数据流
- QImage image;<span style="white-space:pre"> </span>
- receiveMemory.lock();<span style="white-space:pre"> </span>//锁定共享内存
- buffer.setData((char*)receiveMemory.constData(), receiveMemory.size())<span style="white-space:pre"> </span>//用缓冲区得到共享内存关联后得到的数据和数据大小
- buffer.open(QBuffer::ReadOnly);<span style="white-space:pre"> </span>//设置读取模式<span style="white-space:pre"> </span>
- in >> image;<span style="white-space:pre"> </span>//使用数据流从缓冲区获得共享内存的数据，然后输出到字符串中
- receiveMemory.unlock();<span style="white-space:pre"> </span>//解锁
- receiveMemory.detach();<span style="white-space:pre"> </span>//与共享内存空间分离
- ui->lbl_2->setPixmap(QPixmap::fromImage(image));
- //最后是头文件内容
- #include <QWidget>
- #include <QMovie>
- #include <QFile>
- #include <QFileDialog>
- #include <QSharedMemory>
- #include <QBuffer>
- #include <QDebug>
- namespace Ui {
- class Widget;
- }
- class Widget : public QWidget
- {
- Q_OBJECT
- public:
- explicit Widget(QWidget *parent = 0);
- ~Widget();
- void loadfromsharedMem();
- void loadFromMemory();
- public slots:
- void InsertImage();
- private slots:
- void on_btn_1_clicked();
- void on_btn_2_clicked();
- void on_btn_3_clicked();
- void on_btn_4_clicked();
- private:
- Ui::Widget *ui;
- QSharedMemory sharedMemory;
- QSharedMemory receiveMemory;
- };
void Widget::sendtosharedMem()
{
send2sharedMem.setKey("QSharedMemoryExample");
if (send2sharedMem.isAttached())
{
// 将该进程与共享内存段分离
if (!send2sharedMem.detach())
qDebug() << "Unable to detach from shared memory.";
}
bool ok;
QString text = ui->textEdit->toPlainText();
ok = TRUE;
if (ok && text.length())
{
// 将数据加载到共享内存中
QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QDataStream out(&buffer);
out << text;
int size = buffer.size();
// 创建共享内存段
if (!send2sharedMem.create(size))
{
qDebug() << send2sharedMem.errorString() << "\n Unable to create shared memory segment.";
return;
}
send2sharedMem.lock();
char *to = (char*)send2sharedMem.data();
const char *from = buffer.data().data();
memcpy(to, from, qMin(send2sharedMem.size(), size));
send2sharedMem.unlock();
}
else
{
qDebug() << "You must write some texts.";
}
}
这是读取
void MainWidget::recvDate()
{
recvsharedMem..setKey("QSharedMemoryExample");
if (!recvsharedMem.attach())
{
ui->textEdit_2->setText("No Share Data");
return;
}
QBuffer buffer;
QDataStream in(&buffer);
QString text;
recvsharedMem.lock();
buffer.setData((char*)recvsharedMem.constData(), recvsharedMem.size());
buffer.open(QBuffer::ReadOnly);
in >> text;
recvsharedMem.unlock();
recvsharedMem.detach();
ui->textEdit_2->setText(text);
}