Question

I have a pointer that points to first byte of a shared memory which is 66 bytes long. I want to create another pointer that points to a certain byte in shared memory (I’m saying certain byte because I want to get this info from user as integer like:”which byte do you want to reach?”). Is there a way of reaching a certain byte via shared memory’s pointer?

Answer 1

The shared memory part is irrelevant: what you have is a pointer and you want to increment n bytes:

T* p = /* pointer to whatever */;
char* nBytesIn = reinterpret_cast<char*>(p) + n;

Or in your case, more safely:

char* byte_in_buffer(T* p, std::size_t n)
{
    if (n >= 66)
        throw std::out_of_range("Buffer is only 66 bytes!");

    return reinterpret_cast<char*>(p) + n;
}

You need to cast to char* because pointer arithmetic dictates that T* + n increments sizeof(T); we want to increment by bytes, and char is that type (with a size that’s always 1).

(Aliasing a value through a char* is okay.)