Trouble when reading data into buffer using mqqueue

Question

I'm using mqueue to communicate between threads and I'm having a problem passing objects.

The mq_send and mq_receive take a char* as a parameter for the object.

I use them the following way.

foo* foo = new foo();
foo->set_id(3);
mq_send(myQueue, (char*)foo, 1024, 1);

then

char* buffer;
while(true)
{
    ssize_t bytes_read;
    bytes_read = mq_receive(myQueue, buffer, 1024, NULL);
    foo* foo = (foo*) buffer;
    foo->get_id(); //equals 3
    //Send the object to another queue
    mq_send(myOtherQueue, buffer, 1024, 1);
}

So far so good.

The problem is here

    char* buffer;
    while(true)
    {
        ssize_t bytes_read;
        bytes_read = mq_receive(myOtherQueue, buffer, 1024, NULL);
        foo* foo = (foo*) buffer;
        foo->get_id(); //equals garbage 323234234
    }

The second time I cast the buffer, I get garbage. I read about static_cast and dynamic_cast and I can't find what's the problem.

What is wrong?

Answer 1

I see two issues here. First, is your Foo TriviallyCopyable?

Second,

char* buffer;
bytes_read = mq_receive(myOtherQueue, buffer, 1024, NULL);

I do not see any allocation for buffer.