Share multiple segment with QSharedMemory

[boumacmilan]

Hi every body

i want to use QSharedMemory to share data between 2 applications using it for sharing one segment works perfectly but when i try 2 share more than one i have access just to the last one

this my code

sharedMemroy.cpp in the first application

void SharedMemory::loadIntoSharedMem(QString memoryKey,QString &data)
    {
    sharedMem.setKey(memoryKey);
    if (sharedMem.isAttached())
        {
        sharedMem.detach();
        }
    if( data.length())
        {
    // load into shared memory
         QBuffer buffer;
         buffer.open(QBuffer::ReadWrite);
         QDataStream out(&buffer);
         out << data;
         int size = buffer.size();
 
         if (!sharedMem.create(size)) {
             qDebug()<<"Unable to create shared memory segment."<<sharedMem.isAttached()<<" "<<sharedMem.error();
 
         }
 
         sharedMem.lock();
         char *to = (char*)sharedMem.data();
         const char *from = buffer.data().data();
         memcpy(to, from, qMin(sharedMem.size(), size));
         sharedMem.unlock();
        }
    else
        {
          qDebug()<< "no data to share"
        }
 
    }

void SharedMemory::loadIntoSharedMem(QString memoryKey,QString &data)
    {
    sharedMem.setKey(memoryKey);
    if (sharedMem.isAttached())
        {
        sharedMem.detach();
        }
    if( data.length())
        {
    // load into shared memory
         QBuffer buffer;
         buffer.open(QBuffer::ReadWrite);
         QDataStream out(&buffer);
         out << data;
         int size = buffer.size();

         if (!sharedMem.create(size)) {
             qDebug()<<"Unable to create shared memory segment."<<sharedMem.isAttached()<<" "<<sharedMem.error();

         }

         sharedMem.lock();
         char *to = (char*)sharedMem.data();
         const char *from = buffer.data().data();
         memcpy(to, from, qMin(sharedMem.size(), size));
         sharedMem.unlock();
        }
    else
        {
          qDebug()<< "no data to share"
        }

    }

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and i main

SharedMemory sh;
    sh.loadIntoSharedMem("memo1",data1 );
    sh.loadIntoSharedMem("memo2",data2 );
    sh.loadIntoSharedMem("memo3",data3 );

SharedMemory sh;
    sh.loadIntoSharedMem("memo1",data1 );
    sh.loadIntoSharedMem("memo2",data2 );
    sh.loadIntoSharedMem("memo3",data3 );

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and on showSharedData.cpp in the seconde application

QString ShowSharedMemory::loadFromSharedMem(QString memoryKey)
{
    sharedMem.setKey(memoryKey);
    if (!sharedMem.attach())
    {
        qDebug()<<"Unable to load!";
        return"";
    }
 
    QBuffer buffer;
    QDataStream in(&buffer);
    QString text;
 
    sharedMem.lock();
    buffer.setData((char*)sharedMem.constData(), sharedMem.size());
    buffer.open(QBuffer::ReadOnly);
    in >> text;
    sharedMem.unlock();
 
    sharedMem.detach();
    return text;
 
}

QString ShowSharedMemory::loadFromSharedMem(QString memoryKey)
{
    sharedMem.setKey(memoryKey);
    if (!sharedMem.attach())
    {
        qDebug()<<"Unable to load!";
        return"";
    }

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

    sharedMem.lock();
    buffer.setData((char*)sharedMem.constData(), sharedMem.size());
    buffer.open(QBuffer::ReadOnly);
    in >> text;
    sharedMem.unlock();

    sharedMem.detach();
    return text;

}

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and in main

data1=showMemory.loadFromSharedMem("memo1");
      data2=showMemory.loadFromSharedMem("memo2");
      data3=showMemory.loadFromSharedMem("memo3");

data1=showMemory.loadFromSharedMem("memo1");
      data2=showMemory.loadFromSharedMem("memo2");
      data3=showMemory.loadFromSharedMem("memo3");

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thanks for your help

[boumacmilan]

i resolve it by mading 3 object SharedMemory, i know its not a good methode , but it works
(sorry for my bad english)

[anda_skoa]

i resolve it by mading 3 object SharedMemory, i know its not a good methode

I don't think there is an alternative, so it is the right way to do it.

QSharedMemory is a bit like a smart pointer, so you need to keep it around as long as you want to work with the shared memory it is associated with.

Cheers,
_