c语言写一个旋转bmp图像90度的程序

以下是一个用 C 语言编写的旋转 BMP 图像 90 度的程序：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#pragma pack(2)
typedef struct BITMAPFILEHEADER {
    unsigned short bfType;
    unsigned int bfSize;
    unsigned short bfReserved1;
    unsigned short bfReserved2;
    unsigned int bfOffBits;
} BMPFILEHEADER;

typedef struct BITMAPINFOHEADER {
    unsigned int biSize;
    int biWidth;
    int biHeight;
    unsigned short biPlanes;
    unsigned short biBitCount;
    unsigned int biCompression;
    unsigned int biSizeImage;
    int biXPelsPerMeter;
    int biYPelsPerMeter;
    unsigned int biClrUsed;
    unsigned int biClrImportant;
} BMPINFOHEADER;

typedef struct RGBQUAD {
    unsigned char rgbBlue;
    unsigned char rgbGreen;
    unsigned char rgbRed;
    unsigned char rgbReserved;
} RGBQUAD;

typedef struct BITMAPINFO {
    BMPINFOHEADER bmiHeader;
    RGBQUAD bmiColors[1];
} BMPINFO;

#pragma pack()

int main(int argc, char *argv[]) {
    if (argc != 3) {
        printf("Usage: %s [input_filename] [output_filename]\n", argv[0]);
        return 1;
    }

    char *input_filename = argv[1];
    char *output_filename = argv[2];

    FILE *fp_in = fopen(input_filename, "rb");
    if (fp_in == NULL) {
        printf("Cannot open input file: %s\n", input_filename);
        return 1;
    }

    FILE *fp_out = fopen(output_filename, "wb");
    if (fp_out == NULL) {
        printf("Cannot open output file: %s\n", output_filename);
        return 1;
    }

    BMPFILEHEADER file_header;
    BMPINFOHEADER info_header;

    fread(&file_header, sizeof(BMPFILEHEADER), 1, fp_in);
    fread(&info_header, sizeof(BMPINFOHEADER), 1, fp_in);

    int width = info_header.biWidth;
    int height = info_header.biHeight;

    BMPINFOHEADER new_info_header = info_header;

    new_info_header.biWidth = height;
    new_info_header.biHeight = width;

    fwrite(&file_header, sizeof(BMPFILEHEADER), 1, fp_out);
    fwrite(&new_info_header, sizeof(BMPINFOHEADER), 1, fp_out);

    int padding = (4 - ((width * 3) % 4)) % 4;
    int new_padding = (4 - ((height * 3) % 4)) % 4;

    RGBQUAD *palette = NULL;
    if (new_info_header.biBitCount <= 8) {
        int num_colors = new_info_header.biClrUsed ? new_info_header.biClrUsed : (1 << new_info_header.biBitCount);
        palette = (RGBQUAD *)malloc(num_colors * sizeof(RGBQUAD));
        fread(palette, sizeof(RGBQUAD), num_colors, fp_in);
        fwrite(palette, sizeof(RGBQUAD), num_colors, fp_out);
    }

    int i, j;
    unsigned char pixel[3];
    unsigned char *row = (unsigned char *)malloc((width * 3 + padding) * sizeof(unsigned char));
    unsigned char *new_row = (unsigned char *)malloc((height * 3 + new_padding) * sizeof(unsigned char));

    for (i = 0; i < height; i++) {
        fread(row, sizeof(unsigned char), width * 3 + padding, fp_in);
        for (j = 0; j < width; j++) {
            pixel[0] = row[j * 3];
            pixel[1] = row[j * 3 + 1];
            pixel[2] = row[j * 3 + 2];
            memcpy(&new_row[(height - 1 - i) * 3 + j * 3], pixel, 3);
        }
    }

    fwrite(new_row, sizeof(unsigned char), height * 3 + new_padding, fp_out);

    free(row);
    free(new_row);
    if (palette != NULL) {
        free(palette);
    }

    fclose(fp_in);
    fclose(fp_out);

    return 0;
}

这个程序通过读取 BMP 文件头和信息头，计算出图像的宽度和高度，并生成新的信息头，将旋转后的图像写入新的文件。在旋转过程中，程序按照从左到右、从上到下的顺序读取源文件的像素，将其存储到新文件的相应位置。由于 BMP 文件的像素行必须按照 4 字节对齐，程序还需要计算源文件和新文件的填充字节数，并在读写像素行时跳过这些填充字节。