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question about C++ structures

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I have this structure: struct TERRCOORD { WORD height; BYTE lightIntensity; }; So 3 bytes, right? But it turns out sizeof(TERRCOORD) evaluates to 4. I guess the WORD has to align to an even byte or something... right? In my game, this structure is used like so: DWORD terrainSize = 4000000; // or similar TERRCOORD* terrCoords = new TERRCOORD[ terrainSize ]; I really need to keep this data (height & lightIntensity) to 3 bytes/coordinate. How can I do this? I don''t want to have separate height and lightIntensity arrays, because then I''d have to incrememnt two pointers instead of one when processing the coords.

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If you are doing this in windoze w ith VC++ then it pads structures to be aligned on a 32 bit boundry by default. Fool around with the options and see if you can somehow disable padding.


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In MSVC, you can disable padding as follows:

// Byte-align, other values are 2, 4, 8, 16.
#pragma pack(1)
typedef struct
. . .

// Use default padding.

#pragma pack

But usually, you want to leave padding enabled. If a non-naturally sized piece of data is accessed, the processor will do multiple aligned memory accesses to assemble the data.

Edited by - mhkrause on June 26, 2000 10:16:43 PM

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