c++ - How can I refer to sub-elements in a particular variable? -

my problem follows: have 64 bit variable, of type uint64_t (so know it's specified @ least 64 bits wide).

i want able refer different parts of it, example breaking down 2 uint32_ts, 4 uint16_ts or 8 uint8_ts. there standards compliant way doesn't rely on undefined behavior?

my approach follows:

class buffer {   uint64_t m_64bitbuffer;    public:     uint64_t & r64() { return m_64bitbuffer; }     uint32_t & r32(r32::part part) { return *(reinterpret_cast<uint32_t*>(&m_64bitbuffer)+part); }     uint16_t & r16(r16::part part) { return *(reinterpret_cast<uint16_t*>(&m_64bitbuffer)+part); }     uint8_t & r8(r8::part part) { return *(reinterpret_cast<uint8_t*>(&m_64bitbuffer)+part); } }; 

where r32::part, r16::part , r8::part enums define values between 0 , 1, 0 , 3 , 0 , 7 respectively.

i imagine should ok. there should no issues alignment, example. i'd know if i'm breaking rules, , if so, how properly.

type-punning through union allowed compilers, have following anonymous union member:

union {     uint64_t val;     struct { uint32_t as32[2]; };     struct { uint16_t as16[4]; };     struct { uint8_t as8[8]; }; } u; 

access each part easy reading appropriate member.