framebuffer 变量定义 问题点

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>

int main () {
    int fp=0;
    struct fb_var_screeninfo vinfo;
    struct fb_fix_screeninfo finfo;
    long screensize=0;
    unsigned int *fbp = 0;   short 型 和 int 型的区别 ，容易出问题
    int x = 0, y = 0;
    long location = 0;
    fp = open ("/dev/fb0",O_RDWR);

    if (fp < 0){
        printf("Error : Can not open framebuffer device/n");
        exit(1);
    }

    if (ioctl(fp,FBIOGET_FSCREENINFO,&finfo)){
        printf("Error reading fixed information/n");
        exit(2);
    }
   
    if (ioctl(fp,FBIOGET_VSCREENINFO,&vinfo)){
        printf("Error reading variable information/n");
        exit(3);
    }

        screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
    /*这就是把fp所指的文件中从开始到screensize大小的内容给映射出来，得到一个指向这块空间的指针*/
    fbp =(unsigned int *) mmap (0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fp,0);
      if ((int )fbp == -1)
        {
              printf ("Error: failed to map framebuffer device to memory./n");
              exit (4);
        }
      return 0;
}