C++ struct in union acces over union member

Question

i have a Struct which consists of an Union which consists of an uint32_t and another (anonym) struct. It looks like this:

struct sMesswertNummer {
union {
    uint32_t MesswertNummerFull;
    struct {
        uint16_t MesswertNummerPart:16;
        uint16_t AggregatNummer:16;
        uint8_t  AggregatSub:8;
        uint8_t  AggregatTyp:8;
    };
};
sMesswertNummer() { this->MesswertNummerFull=0; }
sMesswertNummer(uint16_t MesswertNummerPart,uint16_t AggregatNummer, uint8_t AggregatSub, uint8_t AggregatTyp) {
    this->MesswertNummerFull=0;
    this->MesswertNummerPart=MesswertNummerPart;
    this->AggregatNummer=AggregatNummer;
    this->AggregatSub=AggregatSub;
    this->AggregatTyp=AggregatTyp;
}
};

I initialze the struct with a Call of the Constructor like this

MesswertNummer(0x0001,0x0002,0x30,0x02);

After that my Variable has the right values, Var.MesswertNummerPart is 0x0001, Var.AggregatNummer is 0x0002 and so on.

But if i call Var.MesswertNummerFull i get 0x0001 (is MesswertNummerPart) instead of 0x023000020001 (0x02->AggregatTyp, 0x30->AggregatSubm 0x0002->AggregatNummer, 0x0001->MesswertNummerPart)

How can i get the whole Number with a call of Var.MesswertNummerFull?

Just solved the Problem by typing it again. MesswertNummerFull has to be a uint64_t (16+16+8+8 = 48) — Haselnussstrauch, Oct 24 '14 at 09:58
Note that this use of unions is technically undefined. You're only supposed to use _one_ field of a union at a time. — Lightness Races in Orbit, Oct 24 '14 at 11:48
Thank you for your answer @Lightness. I'll use masking and shifting instead. — Haselnussstrauch, Oct 27 '14 at 10:22

score 0 · Accepted Answer · answered Oct 24 '14 at 11:36

0

Just solved the Problem by typing it again. MesswertNummerFull has to be a uint64_t (16+16+8+8 = 48)

answered Oct 24 '14 at 11:36

Haselnussstrauch

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C++ struct in union acces over union member

1 Answers1