On 03 Jan 2009, at 12:54, gabor wrote:
I'm trying to convert c header code from "Windows Mobile API 5" to
pascal and I'm getting wrong size of converted record:
original c header:
typedef struct _DDPIXELFORMAT
{
DWORD dwSize;
DWORD dwFlags;
DWORD dwFourCC;
union
{
DWORD dwRGBBitCount;
DWORD dwYUVBitCount;
DWORD dwAlphaBitDepth;
};
union
{
DWORD dwRBitMask;
DWORD dwYBitMask;
};
[snip]
and my pascal conversion:
"union" in C means that the fields inside this union{..} block all
start at the same address, but whatever comes after the union{} block
follows all of those fields. Your translation does exactly the
inverse: it makes all union blocks start at the same address, but puts
the fields inside the union blocks after each other.
I don't think you can create sequential unnamed variant parts in
Pascal records like the above C struct though, but you can get the
same layout and usage by doing this:
PDDPixelFormat = ^TDDPixelFormat;
_DDPIXELFORMAT = record
dwSize: DWORD;
dwFlags: DWORD;
dwFourCC: DWORD;
case Integer of
0: (
dwRGBBitCount : DWORD;
);
1: (
dwYUVBitCount : DWORD;
);
2: (
dwAlphaBitDepth : DWORD;
case Integer of
0: (
dwRBitMask : DWORD;
);
1: (
dwYBitMask : DWORD;
case Integer of
0: (
dwGBitMask : DWORD;
);
1: (
dwUBitMask : DWORD;
case Integer of
0: (
dwBBitMask : DWORD;
);
1: (
dwVBitMask : DWORD;
case Integer of
0: (
dwRGBAlphaBitMask: DWORD;
);
);
);
);
);
end;
In this case it's easy because in each union every field has the same
size. If that weren't the case, you would have to put the nested
variant parts after the largest field of each variant. Or you could
put the variant parts in separate record types and then declare fields
of these types (which is cleaner, but then when accessing the fields
you will have to add the record field names).
Jonas
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