Share multiple segment with QSharedMemory - qt

Question

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"
}
}
and in main
SharedMemory sh;
sh.loadIntoSharedMem("memo1",data1 );
sh.loadIntoSharedMem("memo2",data2 );
sh.loadIntoSharedMem("memo3",data3 );
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;
}
and in main
data1=showMemory.loadFromSharedMem("memo1");
data2=showMemory.loadFromSharedMem("memo2");
data3=showMemory.loadFromSharedMem("memo3");
thanks for your help

Answer 1

Your problem is that second write attempt overwrites all data. You need to implement cross-process containers (boost has some), like QList, if you want to share data via shared memory. It is hard topic.
I propose you to use sockets to send strings between processes. Or other platform depended mechanism (for example, pipes on windows).