Working with data alignment

Processors read and write data not in bytes, but in memory words – chunks that match their data address size. 32-bit processors work with 32-bit words, 64-bit processors with 64-bit words, and so on.

Reads and writes are most efficient when words are aligned – the data address is a multiple of the word size. For example, for 32-bit architectures, the address 0x00000004 is aligned, while 0x00000005 is unaligned. On x86 platform, access to unaligned data is slower that to aligned. On ARM, however, access to unaligned data generates a hardware exception and lead to program termination:

Compilers align data automatically. When it comes to structures, the result may be surprising for developers who are not aware of alignment.
struct {
    uint8_t c;
    uint32_t i;
} a = {1, 1};

std::cout << sizeof(a) <&lt...