brk()和sbrk()的简单练习

 

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
struct User{
 char name[20];
 int telnum;
};
static struct User* UserList;
struct User* Now;
 void
showUser(struct User u)
{
 printf("姓名:%s --- 号码:%d\n",u.name,u.telnum);
}
 struct User
addUser()
{
 Now = sbrk(0);
 Now = sbrk(sizeof(struct User));
 printf("输入添加用户名\n");
 scanf("%s",Now->name);
 printf("输入号码\n");
 scanf("%d",&(Now->telnum));
 printf("添加成功\n");
 return *Now;
}

struct User*
find(const char* name)
{
 struct User* p = UserList;
 struct User* end = sbrk(0);
 for(;p!=end;p++)
 {
  if(!strcmp(name,p->name)) {
   printf("已找到\n"
     "姓名:%s --- 号码:%d\n",p->name,p->telnum);
   return p;
  }
 }
 printf("未找到\n");
 return NULL;
}
void
selectByName()
{
 printf("输入要查找的姓名\n");
 char name[20];
 scanf("%s",name);
 find(name);
 return ;
}
 void
delUser()
{
 printf("输入要删除的姓名:\n");
 char name[20];
 scanf("%s",name);
 struct User *p = find(name);
 if(p==NULL){
  return;
 }else{
  //*p = (struct User)NULL;
  p->name[0] = '\0';
  printf("删除成功\n");
  return;
 }
}
 void
saveFile()
{
 umask(0022);
 int fd = open("USER.DAT",O_RDWR|O_CREAT|O_TRUNC,0666);
 if(fd==-1){
  perror("FILE NO EXCT");
  return;
 }
 struct User* p = UserList;
 struct User* end = sbrk(0);
 for(;p!=end;p++)
 {
  if(p->name[0]!='\0')
   pwrite(fd,p,sizeof(struct User),lseek(fd,0,SEEK_END));
 }
 printf("文件储存完成\n");
 close(fd);
 return;
}
 void
showAll()
{
 struct User* p = UserList;
 struct User* end = sbrk(0);
 for(;p!=end;p++)
 {
  if(p->name[0]!='\0')
   showUser(*p);
 }
 return;
}
void
loadFromFile()
{
 char file[50];
 printf("输入文件路径\n");
 scanf("%s",file);
 int fd = open(file,O_RDONLY);
 if(fd==-1){
  printf("file error\n");
  loadFromFile();
 }
 off_t beg = lseek(fd,0,SEEK_SET);
 off_t end = lseek(fd,0,SEEK_END);
 off_t size = end - beg;
 lseek(fd,0,SEEK_SET);
 read(fd,UserList,size);

 printf("load success!!!\n");
 return ;
}
 int
main()
{
 UserList = sbrk(0);
 Now = sbrk(0);
 int fd = open("USER.DAT",O_RDONLY);
 if(fd==-1){
  printf("file error\n");
  return -1;
 }
 lseek(fd,0,SEEK_SET);
 read(fd,(struct User*)UserList,end-beg);
 close(fd);
 printf("*************************************************\n"
   "通讯录小程序\n"
   "*************************************************\n"
   "[1]显示所有记录\n"
   "[2]添加记录\n"
   "[3]查找记录\n"
   "[4]删除记录\n"
   "[5]文件保存\n"
   "[6]导入文件记录\n"
   "[0]退出\n");
 while(1)
 {
  printf("请选择\n");
  int num = 0;
  scanf("%d",&num);
  switch(num){
   case 1:showAll();break;
   case 2:addUser();break;
   case 3:selectByName();break;
   case 4:delUser();break;
   case 5:saveFile();break;
   case 6:printf("导入文件记录\n");break;
   case 0:saveFile();brk(UserList);exit(0);
  }
 }
}