Size of structs containing unions

From: "luke" <lroluk1@xxxxxxxxx>
Date: 30 Sep 2005 00:23:18 -0700

hi,
in Visula C++ 6.0 I have declared a struct like this:

typedef struct _WRITE_INPUT {

ULONG DeviceNumber;
ULONG RegisterNumber;
union {
USHORT ShortData;
UCHAR CharData;
};
} WRITE_INPUT;

I can't understand why, sizeof(WRITE_INPUT) returns 12. It should
return 10, shouldn't it?

sizeof(ULONG) = 4
sizeof(ULONG) = 4
sizeof(USHORT) = 2 (longest union field)

4 + 4 + 2 = 10

thanks
bye
luke

.

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