在解析C /读取位图文件 [英] Parse/Read Bitmap file in C
问题描述
我试图做一个程序从一个位图文件（.BMP，Windows的文件格式，8位）读取数据。现在我卡上的图像数据读取之前的头。
I'm trying to make a program to read data from a bitmap file (.bmp, Windows file format, 8bit). Right now I'm stuck on reading the headers before the image data.
我用的是规格为BMP，我发现这里的 ，以使这些结构来保存文件头，信息头和图像数据BMP的：
I used the specifications for bmp that I found here to make these structs to hold the file header, info header, and image data of the bmp:
typedef struct {
unsigned char fileMarker1;
unsigned char fileMarker2;
unsigned int bfSize;
uint16_t unused1;
uint16_t unused2;
unsigned int imageDataOffset;
} FILEHEADER;
typedef struct {
unsigned int biSize;
int width;
int height;
uint16_t planes;
uint16_t bitPix;
unsigned int biCompression;
unsigned int biSizeImage;
int biXPelsPerMeter;
int biYPelsPerMeter;
unsigned int biClrUsed;
unsigned int biClrImportant;
} INFOHEADER;
typedef struct {
unsigned char b;
unsigned char g;
unsigned char r;
} IMAGE;
我实在看不出什么毛病，这些（除非我对规范源是错的，但我在其他地方看了看，在我看来，OK）。
I can't really see anything wrong with these (unless my source for the specification is wrong, but I've looked elsewhere and it seems to me ok).
我用下面的code，以测试它被正确解析：
I'm using the following code to test that it gets parsed correctly:
int main(void) {
FILEHEADER fh;
INFOHEADER ih;
FILE *img = fopen("img.bmp", "rb");
fread(&fh, sizeof(unsigned char), sizeof(FILEHEADER), img);
fread(&ih, sizeof(unsigned char), sizeof(INFOHEADER), img);
printf("fM1 = %c, fM2 = %c, bfS = %u, un1 = %hu, un2 = %hu, iDO = %u\n", fh.fileMarker1, fh.fileMarker2, fh.bfSize, fh.unused1, fh.unused2, fh.imageDataOffset);
printf("w = %d, h = %d\n", ih.width, ih.height);
return 0;
}
不幸的是，当我运行此我得到一个错误的结果：
Unfortunately when I run this I get a wrong result:
User$ ./images
fM1 = B, fM2 = M, bfS = 0, un1 = 0, un2 = 118, iDO = 2621440
w = 3276800, h = 65536
根据该链接，unused1和2应该总是0。此外，宽度和高度是完全错误（这是一个16×16的图像）。
According to that link, unused1 and 2 should be always 0. Also, the width and height are completely wrong (it's a 16x16 image).
似乎有某种对齐问题与结构回事。有没有人有这样的经验吗？ （我不希望使用任何图像/位图图库，我要做到这一切我自己）。
it seems that there is some sort of alignment issue going on with the structures. Does anyone have any experience with this? (I don't want to use any image/bitmap libraries, I want to do all this myself).
感谢您的帮助！
推荐答案
是啊，我忘了收拾的结构。这解决的事情。哎呀：
Yup I forgot to pack the structs. This fixes things. Oops:
typedef struct __attribute__((__packed__)) {
unsigned char fileMarker1;
unsigned char fileMarker2;
unsigned int bfSize;
uint16_t unused1;
uint16_t unused2;
unsigned int imageDataOffset;
} FILEHEADER;
typedef struct __attribute__((__packed__)) {
unsigned int biSize;
int width;
int height;
uint16_t planes;
uint16_t bitPix;
unsigned int biCompression;
unsigned int biSizeImage;
int biXPelsPerMeter;
int biYPelsPerMeter;
unsigned int biClrUsed;
unsigned int biClrImportant;
} INFOHEADER;
typedef struct __attribute__((__packed__)) {
unsigned char b;
unsigned char g;
unsigned char r;
} IMAGE;
这篇关于在解析C /读取位图文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
