Cast array of bytes to POD

Question

Let\'s say, I have an array of unsigned chars that represents a bunch of POD objects (e.g. either read from a socket or via mmap). Which types they represent and at what positi

Answer 1

Using a union allows to escape anti-aliasing rule. In fact that is what unions are for. So casting pointers to a union type from a type that is part of the union is explicitly allowed in C++ standard (Clause 3.10.10.6). Same thing is allowed in C standard (6.5.7).

Therefore depending on the other properties a conforming equivalent of your sample can be as follows.

union to_pod {
    uint8_t buffer[100];
    Pod1 pod1;
    Pod1 pod2;
    //...
};

uint8_t buffer[100]; //filled e.g. from network

switch(buffer[0]) {
    case 0: process(reinterpret_cast(buffer + 4)->pod1); break;
    case 1: process(reinterpret_cast(buffer + 8 + buffer[1]*4)->pod2); break;
    //...
}