用read函数完成图片文件拷贝

#include<stdio.h>
#include<head.h>
int main(int argc, const char *argv[])
{//umask(0);//将文件权限掩码改为0，使得其他用户可写int fd = open("/home/ubuntu/图片/2.jpg",O_RDONLY,0777);//打开图片if(fd<0){   ERR_MSG("open");return -1; }   printf("打开成功\n");int ff = open("1.jpg",O_WRONLY|O_CREAT|O_TRUNC,0777);//创建图片if(ff<0){   ERR_MSG("open");return -1; }   printf("打开成功\n");char a[20]="";ssize_t res;while(1){   res=read(fd,a,sizeof(a)-1);if(0==res)break;if(write(ff,a,res)<0){ERR_MSG("write");return -1; }}   printf("拷贝完成\n");if(close(fd)<0){   ERR_MSG("close");return -1;                                                                                  }   printf("关闭成功\n");if(close(ff)<0){   ERR_MSG("close");return -1; }   printf("关闭成功\n");return 0;
} 

用read实现计算文件大小

#include<stdio.h>
#include<head.h>
int main(int argc, const char *argv[])
{int ff = open("1.jpg",O_RDONLY);if(ff<0){   ERR_MSG("open");return -1; }   printf("打开成功\n");off_t size=lseek(ff,0,SEEK_END);printf("图片大小为:%ld\n",size);char a;long count=0;                                                                                                                lseek(ff,0,SEEK_SET);while(read(ff,&a,1)>0){   count++;}   printf("图片大小为:%ld\n",count);if(close(ff)<0){   ERR_MSG("close");return -1; }   printf("关闭成功\n");return 0;
} 

 将文件权限提取修改成循环方式

#include<stdio.h>
#include<head.h>
void get_filePermission(mode_t m)
{int a[9]={0400,0200,0100,0040,0020,0010,0004,0002,0001};char b[9]={'r','w','x','r','w','x','r','w','x'};for(int i=0;i<9;i++){   if((m&a[i])==0)putchar('-');elseputchar(b[i]);}   
}
int main(int argc, const char *argv[])
{struct stat buf;if(stat("./time.c",&buf)<0){   ERR_MSG("stat");return -1; }   printf("mode: 0%o\n",buf.st_mode);get_filePermission(buf.st_mode);printf("\n");printf("link: %ld\n",buf.st_nlink);printf("uid: %d\n",buf.st_uid);printf("gid: %d\n",buf.st_gid);printf("size: %ld\n",buf.st_size);printf("time: %ld\n",buf.st_ctime);return 0;
}