How to keep a pointer on a shared data in a boost shared memory segment

Question

How to keep a pointer on a shared data in a boost shared memory segment ?

I have a function which returns:

shm.construct<SharedData>(_nameSeg.c_str())(innerDataAllocator);

But outside of the function, the object pointed by SharedData is inaccessible. Why ?

My general problem is that I want to have a way to get, and set data in shared memory, but without, each time, having to :

• get shm
• find object in shm based on its name
• construct allocators.

So what I'm trying to do is to store in a struct:

• allocators
• a pointer to the shared object

Is it a good idea/design ? How could I do this ?

EDIT

Here is the type of class I would like to have, it's a singleton storing the info of the current shm:

typedef bip::allocator<wchar_t, bip::managed_shared_memory::segment_manager> CharAllocator;
typedef bip::basic_string<wchar_t, std::char_traits<wchar_t>, CharAllocator> MyShmString;

class InnerData {
public:
    uint64_t id;
    MyShmString name;
    uint8_t status;
    static const uint8_t defaultStatus = 3;

    InnerData(CharAllocator cAlloc):name(cAlloc) {

    }
};

typedef bip::allocator<InnerData, bip::managed_shared_memory::segment_manager> InnerDataAllocator;
class Zone {
public:
    SharedData * sharedData;

    CharAllocator     charAllocator;
    InnerDataAllocator   innerDataAllocator;

    Zone():{} //here I need to initialize charAllocator and innerDataAllocator with shm.get_segment_manager(),
              // because bip::allocators don't have default constructors


    static Zone create(std::string &_name, std::string &_nameSeg); 
    static Zone get(std::string &_name, std::string &_nameSeg);
    static Zone delete(std::string &_name, std::string &_nameSeg);
    void putInShm(const std::vector<UsualInnerData> &in);
    static bool alreadyCreated;
};

in .cpp

Zone::create(std::string &_name, std::string &_nameSeg){
     //create the shm
     // create allocators charAllocator and innerDataAllocator, passing shm.get_segment_manager()
     //construct the sharedData object (with shm.construct<SharedData>(_nameSeg.c_str())(innerDataAllocator))
     //create a Zone
     Zone z(charAllocator, innerDataAllocator, sharedData );
     return z;
}

In this case, the Zone constructor would be:

Zone(CharAllocator _charAllocator, InnerDataAllocator _innerDataAllocator, SharedData* _sharedData):
    charAllocator(_charAllocator),
    innerDataAllocator(_innerDataAllocator),
    sharedData(_sharedData)
{}

But then, as I said, once we quit Zone::Create, the data to where the SharedData pointer (which is inside the returned Zone z) points to, is de-allocated memory.

And the second problem is in Zone::putInShm:

void Zone::putInShm(const std::vector<UsualInnerData> &in){
        InnerData newInnerData (charAllocator);
        MyShmString newShmString(charAllocator)
    for (auto a : in) {
        newInnerData.id = a.id;
        newShmString = a.name.c_str();//Here I get an access violation, which means charAllocator is bad ?
        newInnerData.name = newShmString 
        sharedData->data.push_back(newInnerData);
    }
    return;
}

EDIT 2:

Here is a minimal, compilable code. It reproduces the errors described above: https://uploadfiles.io/8o8zo password: stackoverflow