Boost共享内存对象中的指针

Question

I am dealing with boost::interprocess::shared_memory_object and what I'm trying to achieve is like this.

I define my own class which is called SharedMemory and in it, there is a method called CreateSharedMemory() which creates a memory block. I need to keep three arrays Foo a1[SIZE], Foo a2[SIZE] and Foo a3[SIZE] in this memory block such that I can consistently write data into them. Foo is my own defined class. To access these three arrays, I need to get their address in my process. So I pass three pointers Foo *p1, *p2, *p3 to this method to record their addresses. Everything goes well in this method but once it steps out this method, p1, p2, p3 point to the wrong address. Can anyone help?

// Foo.h
class Foo
{
   double f[MAX_SIZE];
   char c[MAX_SIZE];
}

// SharedMemory.cpp
void SharedMemory::CreateSharedMemory(Foo *p1, Foo *p2, Foo *p3)
{
   boost::interprocess::shared_memory_object shm
      (boost::interprocess::create_only
      ,"foo"              //name
      ,boost::interprocess::read_write
      );
   shm.truncate(blockSize);

   //Map the whole shared memory in this process
   boost::interprocess::mapped_region region(shm, boost::interprocess::read_write);
   //Write all the memory to 0
   memset(region.get_address(), 0, region.get_size());

   // assign address
   p1 = static_cast<Foo *>(region.get_address());
   p2 = static_cast<Foo *>(region.get_address() + blockSize / 3);
   p3 = static_cast<Foo *>(region.get_address() + 2 * blockSize / 3);

   // p1, p2, p3 point to the correct address here
}

// p1, p2, p3 point to the wrong address once it steps out CreateSharedMemory()

Answer 1

You must pass a reference to Foo pointer. Like:

void SharedMemory::CreateSharedMemory(Foo* & p1, Foo* & p2, Foo* &p3)