| First attach a file read and write operation: (Today, the head is dizzy, fast into a pig brain ^_^)
Write functions,
#include <unistd.h>
ssize_t write (int fd,const void *buf,size_t nbytes));
Return value: Successfully returns the number of bytes written to the file, failure returns-1
The Write function writes nbytes byte data to the Filedes file, and the data source is BUF.
ssize_t read (int fd,const void *buf,size_t nbytes);
Return value: Successfully returns the number of bytes written, and 0 encounters EOF. Failure return-1
The read function reads Nbytes byte data from the Filedes file and stores it in BUF.
#include <fcntl.h>
int open (const char *pathname,int oflag,mode_t mode)
Return file handle
The first parameter is the pathname of the file to be opened/created, and Oflag is used to specify the open/create mode of the file, which can be logically constituted by the following constants.
O_rdonly Read Only mode Ycwlinux Federation
O_wronly only write mode Ycwlinux Federation
O_RDWR reading and writing mode Ycwlinux Alliance
When you open/create a file, you must use at least one of the three above to match the following:
O_append writes each write to the end of the file Ycwlinux Federation
O_creat This file is created if the specified file does not exist Ycwlinux Federation
O_EXCL If the file you want to create already exists, return-1 and modify the value of errno Ycwlinux Federation
O_trunc if the file exists and is opened in write/read-only mode, empty the entire contents of the File Ycwlinux Federation
O_noctty if the path name points to a terminal device, do not use it as a control terminal. Ycwlinux Alliance
O_nonblock if the path name points to a fifo/block file/character file, then the file is opened and subsequent I/oycwlinux Federation
Set to Non-blocking (nonblocking mode)
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#define N 10
typedef struct NODE
{
Char name[20];
struct node *next;
}stud; To write a linked list to a file
Stud * Create (int n)
{
Stud *p,*h,*s;
int i;
H=null; Often forget to define here, causing the following to execute segment fault!!
for (i=0;i<n;i++)
{
if ((s= (Stud *) malloc (sizeof (stud))) ==null)
{
printf ("malloc space failed!\n");
Exit (0);
}
if (h==null)
H=s;
Else
p->next=s;
printf ("Please enter Name:");
scanf ("%s", s->name);
P=s;
}
s->next=null;
return h;
} void print (STUD * head)
{
while (head)
{
printf ("name:%s\n", head->name);
head=head->next; } } Read a list from a file
Stud * Read_userman ()
{
int FD,USERSIZE,RC;
Stud *P1,*P2;
Stud temp;
Static stud head;
Usersize=sizeof (stud);
Fd=open ("/tmp/user.txt", o_creat| O_RDONLY);
if (fd<0)
Return
Rc=read (fd,&temp,usersize);
p1=&head;
while (rc>0)
{
p1->next= (Stud *) malloc (usersize);
memcpy (p1->next,&temp,usersize);
p1=p1->next;
p1->next=null;
memset (&temp,0,usersize);
Rc=read (fd,&temp,usersize);
}
Close (FD);
if (P1==&head)
return NULL;
return head.next;
} int main ()
{
Stud *head;
Head=create (N);
Print (head);
Write_username (head);
Head=read_userman ();
Print (head);
return 0;
} When the linked list is read frequently, it can cause program errors. The following procedure for a delete n data, the original approach to delete a write file, delete a write file, frequent operation, will cause the process of death. So the procedure is to delete n data once, all in memory, until all the data is deleted, then write back to the file. This will not cause the death of the process. int Delete_sslclient_userman_memonry ()
{
struct Sslclient_userman First_userman,*userman,*pre_userman;
FILE *FP;
Char usernum[10];
int id;
Userman=read_sslclient_userman_conf ();
First_userman.next=userman;
pre_userman=&first_userman; Fp=fopen ("/tmp/user.txt", "R");
while (1)
{
if (fgets (USERNUM,10,FP) ==null)
break;
Id=atoi (usernum);
while (userman->user_num!=id) && (userman->next!= NULL) {
pre_userman=userman;
userman=userman->next
}
if (userman->next==null)
{
pre_userman->next=null;
& nbsp; write_sslclient_userman_conf (First_userman.next);
return 1;
}
Else
{
pre_userman->next=userman->next;
}
Userman=first_userman.next;
}
Write_sslclient_userman_conf (first_userman.next);
return 0;
} |
