Question

我试图使用 strutct 来绘制 BitMap 文件的地图页头。编辑器似乎正在对齐 4 byte (32bit), 但我需要 2Byte 。我试图通过以下的遵守指令来更改它。

#pragma pack(2)

和

__attribute__ ((aligned(xx)));

those two doesn t seem to have any effect. Is there another way to do this? I m using XCode 4.3 on Mac OS X Lion. I Tested both Apple LLVM 和 Apple GCC compliers.

这里是斯特鲁茨类型定义

typedef struct {
    int16_t bfType; 
    int32_t bfSize;
    int16_t bfReserved1;
    int16_t bfReserved2;
    int32_t bfOffBits;
    int32_t biSize;
    int32_t biWidth;
    int32_t biHeight;
    int16_t biPlanes;
    int16_t biBitCount;
    int32_t biComression;
    int32_t biSizeImage;
    int32_t biXPelsPerMeter;
    int32_t biYPelsPerMeter;
    int32_t biClrUsed;
    int32_t biClrImportant;
} THeader;

Answer 1

记住,背面的长袍可能在别的地方被翻了?

#include <inttypes.h>
#include <stddef.h>

#pragma pack(push,2)

typedef struct {
int16_t bfType; 
int32_t bfSize;
int16_t bfReserved1;
int16_t bfReserved2;
int32_t bfOffBits;
int32_t biSize;
int32_t biWidth;
int32_t biHeight;
int16_t biPlanes;
int16_t biBitCount;
int32_t biComression;
int32_t biSizeImage;
int32_t biXPelsPerMeter;
int32_t biYPelsPerMeter;
int32_t biClrUsed;
int32_t biClrImportant;
} THeader;

#pragma pack(pop)

#include <stdio.h>

int main(void)
{
printf("%lu
", offsetof(THeader, bfType));
printf("%lu
", offsetof(THeader, bfSize));
printf("%lu
", offsetof(THeader, bfReserved1));
printf("%lu
", offsetof(THeader, bfReserved2));
return 0;
}


$ clang -o pack pack.c
$ ./pack
0
2
6
8

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