Getting offset_ptr of object in shared memory

How can i access the offset_ptr of the object which is created in the shared memory?

segment = new managed_shared_memory(create_only, "MySharedMemory", segmentSize);  
line = 开发者_运维知识库segment->construct<Line>("Line1")("line");

I want to access of offset_ptr for Line object..

First, you need to declare the offset pointer with your Line type:

boost::interprocess::offset_ptr<Line> offset_p;

Second, you assign it:

offset_p = line;

Now, offset_p holds an offset from from line to itself, so you can get a pointer to line and use it in any process like this:

draw_line( offset_p.get() );