Qt主要是通過QSharedMemory類來訪問以及操作共享內存。
以下是幾個主要的步驟
1.對於QsharedMemory類的對象進行創建
利用QSharedMemory類創建實例對象時，必須爲該共享內存指定關鍵字(即爲該共享內存起一個名字)。只有當共享內存被設置了關鍵字之後，纔可以執行創建create()、關聯attach()等操作。爲共享內存指定關鍵字有兩種方法：
a.直接在通過構造函數來進行關鍵字設置：
比如：
QSharedMemory sendsharedMem;
QSharedMemory recvsharedMem;
MainWidget::MainWidget(QWidget *parent) :
QWidget(parent),sendsharedMem("SHAREFILE"),recvsharedMem("SHAREFILE")直接這樣設置key
b. 對象構造好之後利用setKey來進行設置
比如：
sendsharedMem.setKey("SHAREFILE");
recvsharedMem.setKey("SHAREFILE");這樣來設置
2、創建共享內存
QSharedMemory::ReadOnly 只讀方式訪問共享內存
QSharedMemory::ReadWrite 讀寫方式訪問共享內存
3、關聯共享內存
bool QSharedMemory::attach ( AccessMode mode =ReadWrite )
4、分離共享內存
bool QSharedMemory::detach ()
5、判斷共享內存的關聯狀態
bool QSharedMemory::isAttached ()const
void QSharedMemory::setKey (const QString & key ) //設定共享內存關鍵字
6、鎖定/解鎖共享內存
bool QSharedMemory::lock () //鎖定共享內存
bool QSharedMemory::unlock () //解鎖共享內存
界面是這樣，open用來打開本地圖片並在左邊label顯示，save用來存儲進共享空間，show用來讀取共享空間的圖在右邊label顯示，exit是退出
//首先是打開本地圖片並顯示
void Widget::InsertImage()
{
ui->btn_1 = qobject_cast<QPushButton*>(sender());
QString fileName = QFileDialog::getOpenFileName( this,
tr("打開文件"),
"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();
}//然後是存儲共享空間
void Widget::loadfromsharedMem()
{
sharedMemory.setKey("QSharedMemoryExample");<span style="white-space:pre"> </span>// 設置訪問標識
if (sharedMemory.isAttached())<span style="white-space:pre"> </span>//判斷是否連接到共享塊
{
// 將該進程與共享內存段分離
if (!sharedMemory.detach())
qDebug() << "Unable to detach from shared memory.";
}
QString fileName = QFileDialog::getOpenFileName(0, tr("打開文件"),
"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;
}
// 將數據加載到共享內存中
QBuffer buffer; <span style="white-space:pre"> </span>//將字符串轉換爲字節的介質
buffer.open(QBuffer::ReadWrite);<span style="white-space:pre"> </span>//設置讀取模式
QDataStream out(&buffer);<span style="white-space:pre"> </span>//數據流
out << image;
int size = buffer.size();<span style="white-space:pre"> </span>//獲得字節大小
// 創建共享內存段
if (!sharedMemory.create(size))<span style="white-space:pre"> </span>//檢測共享內存是否創建成功
{
qDebug() << sharedMemory.errorString() << "\n Unable to create shared memory segment.";
return;
}
sharedMemory.lock();<span style="white-space:pre"> </span>//鎖定共享內存
char *to = (char*)sharedMemory.data();<span style="white-space:pre"> </span>//共享內存的數據
const char *from = buffer.data().data();<span style="white-space:pre"> </span>//被共享內存的數據
memcpy(to, from, qMin(sharedMemory.size(), size));<span style="white-space:pre"> </span>//將要共享的內存copy到被共享的內存
sharedMemory.unlock();
}<span style="font-family:Arial;"><span style="line-height: 26px;">//接下來是讀取
void Widget::loadFromMemory()
{
receiveMemory.setKey("QSharedMemoryExample");<span style="white-space:pre"> </span>//聲明共享內存的密鑰
// 將共享內存與該進程綁定
if (!receiveMemory.attach())
{
ui->lbl_2->setText("Unable to attach from shared memory.");
return;
}
// 從共享內存中讀取數據
QBuffer buffer;<span style="white-space:pre"> </span>//聲明緩衝區
QDataStream in(&buffer)<span style="white-space:pre"> </span>//聲明數據流
QImage image;<span style="white-space:pre"> </span>
receiveMemory.lock();<span style="white-space:pre"> </span>//鎖定共享內存
buffer.setData((char*)receiveMemory.constData(), receiveMemory.size())<span style="white-space:pre"> </span>//用緩衝區得到共享內存關聯後得到的數據和數據大小
buffer.open(QBuffer::ReadOnly);<span style="white-space:pre"> </span>//設置讀取模式<span style="white-space:pre"> </span>
in >> image;<span style="white-space:pre"> </span>//使用數據流從緩衝區獲得共享內存的數據，然後輸出到字符串中
receiveMemory.unlock();<span style="white-space:pre"> </span>//解鎖
receiveMemory.detach();<span style="white-space:pre"> </span>//與共享內存空間分離
ui->lbl_2->setPixmap(QPixmap::fromImage(image));//最後是頭文件內容
#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;
};如果是lineEdit輸入文字也是很簡單的
void Widget::sendtosharedMem()
{
send2sharedMem.setKey("QSharedMemoryExample");
if (send2sharedMem.isAttached())
{
// 將該進程與共享內存段分離
if (!send2sharedMem.detach())
qDebug() << "Unable to detach from shared memory.";
}
bool ok;
QString text = ui->textEdit->toPlainText();
ok = TRUE;
if (ok && text.length())
{
// 將數據加載到共享內存中
QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QDataStream out(&buffer);
out << text;
int size = buffer.size();
// 創建共享內存段
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.";
}
}
這是讀取
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);
}
