Why is word alignment necessary?

Question

C++ / C#

Why does it add efficiency to the program code? What prevents addressing at odd addresses and why the structure

struct block{
char a;
char b;
char* c;
};

takes not 16, but 8 bytes (in a 32-bit program)? If the compiler generates instead of this structure such

struct decoratedblock{
char a;
char zero[1];
char b;
char zero[1];
char* c;
};

It turns out that b can be located at an address that is not a multiple of a 32-bit machine word. Why is there not 3, but 1 null byte between a and b? Please tell me I'm a little confused

Answer 1

Most modern processors read data from memory not in separate bytes, but in blocks of 2-4-8 bytes. Accordingly, if your data is not aligned in memory and the beginning falls into one block and the end into another, then you will need to get two such blocks to read.

Answer 2

Because the size of the pointer is 4 bytes, so the rest of the elements are aligned on 4