内存

#include<unistd.h>
int brk(void* addr); 
void* sbrk(intptr_t increment);

int err = brk(old);
/**或者brk(p);效果与sbrk(-MAX*MAX);是一样的，但brk()更方便与清晰明了。**/
if(-1 == err){
    perror("brk");
    exit(EXIT_FAILURE);
}

#incldue<sys/mman.h>
void * mmap(void * addr, size_t length,int prot,int flags,int fd,off_t offset);

int munmap(void * addr, size_t length);
// addr为mmap函数返回接收的地址，length为请求分配的长度。

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
main(){
    int fd;
    void *start;
    struct stat sb;
    fd = open("/etc/passwd", O_RDONLY); /*打开/etc/passwd */
    fstat(fd, &sb); /* 取得文件大小 */
    start = mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
    if(start == MAP_FAILED) /* 判断是否映射成功 */
        return;
    printf("%s", start); 
    munmap(start, sb.st_size); /* 解除映射 */
    closed(fd);
}

#include <unistd.h>  
#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;
    char* fbp = 0;
    int x = 0, y = 0;
    long location = 0;
    fp = open("/dev/fb0", O_RDWR);
    sleep(10);
    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 = (char*)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);
    }
    /*这是你想画的点的位置坐标,(0，0)点在屏幕左上角*/
    x = 100;
    y = 100;

    for (x = 100; x < 200; x++)
    {
        for (y = 100; y < 200; y++)
        {
            location = x * (vinfo.bits_per_pixel / 8) + y * finfo.line_length;
            *(fbp + location) = 0;  /* 蓝色的色深 */  /*直接赋值来改变屏幕上某点的颜色*/
            *(fbp + location + 1) = 0; /* 绿色的色深*/
            *(fbp + location + 2) = 200; /* 红色的色深*/
            *(fbp + location + 3) = 0;  /* 是否透明*/
        }
    }

    munmap(fbp, screensize); /*解除映射*/
    close(fp);    /*关闭文件*/
    return 0;
}