union
{ int i;
bool b;
} x;
x.i = 20000;
x.b = true;
cout << x.i;
It prints out 19969. Why does it not print out 20000?
union { int i; bool b; } x; x.i = 20000; x.b = true;
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union
{ int i;
bool b;
} x;
x.i = 20000;
x.b = true;
cout << x.i;
It prints out 19969. Why does it not print out 20000?
A
unionis not astruct. In aunion, all of the data occupies the same space and can be treated as different types via its field names. When you assigntruetox.b, you are overwriting the lower-order bits of20000.More specifically:
20000 in binary: 100111000100000
19969 in binary: 100111000000001
What happened here was that you put a one-byte value of 1 (00000001) in the 8 lower-order bits of 200000.
If you use a
structinstead of aunion, you will have space for both anintand abool, rather than just anint, and you will see the results you expected.