IO进程线程Day2

用fwrite 和 fseek功能，将一张bmp格式的图片更改成 德国国旗

#include <myhead.h>
int main(int argc, const char *argv[])
{
    FILE *fp=fopen("./ceshi.bmp","r+");
    if(NULL==fp){
        perror("open error");
        return -1;
    }
    //读取图片大小
    fseek(fp,2,SEEK_SET);
    int bmp_size=0;
    fread(&bmp_size,4,1,fp);
    printf("图片大小:%d\n",bmp_size);
    //读取图片宽度
    fseek(fp,18,SEEK_SET);
    int bmp_w;
    fread(&bmp_w,4,1,fp);
    printf("图片宽度:%d\n",bmp_w);

    //读取图片高度
    int bmp_h;
    fread(&bmp_h,4,1,fp);
    printf("图片宽度:%d\n",bmp_h);

    //定义一个像素点的大小
    unsigned char bgr1[3]={0,255,255};
    unsigned char bgr2[3]={0,0,255};
    unsigned char bgr3[3]={0,0,0};
    fseek(fp,54,SEEK_SET);
    int num=bmp_w*bmp_h;
    int count=0;
    for(int i=0;i<bmp_w;i++){
        for(int j=0;j<bmp_h;j++){
            count++;
            if(count<=num/3){
                fwrite(bgr1,3,1,fp);              
            }
            else if(count>num/3&&count<=num*2/3){
                fwrite(bgr2,3,1,fp);
            }
            else if(count>num*2/3&&count<=num){
                fwrite(bgr3,3,1,fp);
            }
        }
    }
    fclose(fp);
    return 0;
}