brk()和sbrk()的简单练习

最新推荐文章于 2024-08-21 14:46:06 发布

原创最新推荐文章于 2024-08-21 14:46:06 发布 · 606 阅读

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本文介绍了一个简单的通讯录小程序的功能实现，包括添加、查找、删除联系人及文件保存与导入功能。

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#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);
}
}
}

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