Getting pointers to managed_shared_memory of boost interprocess

Question

In all examples of boost interprocess, I only see it being initialized in main().

#include <boost/interprocess/managed_shared_memory.hpp>
#include <iostream>

using namespace boost::interprocess;

int main()
{
  shared_memory_object::remove("Boost");
  managed_shared_memory managed_shm(open_or_create, "Boost", 1024);
  int *i = managed_shm.construct<int>("Integer")(99);
  std::cout << *i << '\n';
  std::pair<int*, std::size_t> p = managed_shm.find<int>("Integer");
  if (p.first)
    std::cout << *p.first << '\n';
}

Rather than specifically a boost question, this is more of a C++ question where I know i can create an object and initialize managed_shm using the initialization list, but I want to know if there is a way to declare it like managed_shared_memory * managed_shm; and later initialize it like managed_shm = new managed_shm(open_or_create, "Boost", 1024);?

I have seen the managed_shared_memory header, and they didn't seem to provide any option to do so.

Answer 1

Yeah sure. Just write it like that.

#include <boost/interprocess/managed_shared_memory.hpp>
#include <iostream>

namespace bip = boost::interprocess;

struct MyWorker : boost::noncopyable {
    MyWorker() 
        : _shm(new bip::managed_shared_memory(bip::open_or_create, "089f8a0f-956a-441d-9b9e-e0696c43185f", 10ul<<20)) 
    {}

    ~MyWorker() {
        delete _shm;
    }
  private:
    bip::managed_shared_memory* _shm;
};

int main() {
    MyWorker instance;
}

Live On Coliru using managed_mapped_file instead of shared memory (which isn't supported on Coliru)

Of course, prefer smart pointers.

Or indeed, ask yourself why you need dynamic allocation (I cannot think of a valid reason for this)

I you use some kind of API that (mistakenly!) requires a pointer, just take the address:

bip::managed_shared_memory shm(bip::open_or_create, "SHM_NAME", 10ul<<20);

// calling a badly design API takes a pointer:
misguided_api_foo(&shm);