转换工具将jpg格式转换为bmp格式

### 代码样例 ###
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <windows.h>
#define BYTE unsigned char

int main(int argc, char **argv)
{
    if(argc != 3){
        fprintf(stderr, "Usage : ./jpg2bmp.exe inputfile outputfile\n");
        return -1;
    }

    // 打开输入文件
    FILE *fp = fopen(argv[1], "rb");
    if(fp == NULL){
        fprintf(stderr, "fopen %s error\n", argv[1]);
        return -1;
    }

    // 读取文件头
    BYTE head[54];
    if(fread(head, sizeof(BYTE), 54, fp) != 54){
        fprintf(stderr, "read %s error\n", argv[1]);
        fclose(fp);
        return -1;
    }

    // 判断是否是BMP格式
    if(head[0] != 'B' || head[1] != 'M'){
        fprintf(stderr, "%s is not BMP format\n", argv[1]);
        fclose(fp);
        return -1;
    }

    // 获取图像尺寸
    int width = *(int *)(&head[18]);
    int height = *(int *)(&head[22]);

    // 创建位图图像数据数组
    BYTE *data = (BYTE *)malloc(sizeof(BYTE) * width * height * 3);
    if(data == NULL){
        fprintf(stderr,"malloc data error\n");
        fclose(fp);
        return -1;
    }

    // 读取图像像素点数据
    int ret = fread(data, sizeof(BYTE), width * height * 3, fp);
    if(ret != width * height * 3){
        fprintf(stderr,"read %s pixel data error\n", argv[1]);
        fclose(fp);
        free(data);
        return -1;
    }

    fclose(fp);

    // 创建输出文件
    FILE *ofp = fopen(argv[2], "wb");
    if(ofp == NULL){
        fprintf(stderr, "fopen %s error\n", argv[2]);
        free(data);
        return -1;
    }

    // 写入BMP文件头
    if(fwrite(head, sizeof(BYTE), 54, ofp) != 54){
        fprintf(stderr, "write %s bmp header error\n", argv[2]);
        fclose(ofp);
        free(data);
        return -1;
    }

    // 写入图像数据
    if(fwrite(data, sizeof(BYTE), width * height * 3, ofp) != width * height * 3){
        fprintf(stderr, "write %s pixel data error\n", argv[2]);
        fclose(ofp);
        free(data);
        return -1;
    }

    fclose(ofp);
    free(data);
    return 0;
}