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#include <sys/select.h>
int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
参数:
- nfds:监控的文件描述符集里最大文件描述符加1,因为此参数会告诉内核检测前多少个文件文件描述符
- readfs:监控有读数据到达文件描述符集合,传入传出参数
- writefds:监控写数据到达文件描述符集合,传入传出参数
- exceptfds:监控异常发生到达文件描述符集合,如带外数据到达异常,传入传出参数
- timeout:定时阻塞监控时间。
#include <sys/select.h>
void FD_CLR(int fd, fd_set *set); //把文件描述符集里fd位清0
int FD_ISSET(int fd, fd_set *set); //测试文件描述符集里fd是否置1
void FD_SET(int fd, fd_set *set); //把文件描述符集合里fd位置1
void FD_ZERO(fd_set *set); //把文件描述符集合里所有位清0
二、select函数用法图解
三、实验一
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
void perr_exit(const char *s)
{
perror(s);
exit(-1);
}
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr)
{
int n;
again:
if ((n = accept(fd, sa, salenptr)) < 0)
{
//ECONNABORTED 发生在重传(一定次数)失败后,强制关闭套接字
//EINTR 进程被信号中断
if ((errno == ECONNABORTED) || (errno == EINTR))
{
goto again;
}
else
{
perr_exit("accept error");
}
}
return n;
}
int Bind(int fd, const struct sockaddr *sa, socklen_t salen)
{
int n;
if ((n = bind(fd, sa, salen)) < 0)
{
perr_exit("bind error");
}
return n;
}
int Connect(int fd, const struct sockaddr *sa, socklen_t salen)
{
int n;
n = connect(fd, sa, salen);
if (n < 0)
{
perr_exit("connect error");
}
return n;
}
int Listen(int fd, int backlog)
{
int n;
if ((n = listen(fd, backlog)) < 0)
{
perr_exit("listen error");
}
return n;
}
int Socket(int family, int type, int protocol)
{
int n;
if ((n = socket(family, type, protocol)) < 0)
{
perr_exit("socket error");
}
return n;
}
ssize_t Read(int fd, void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ( (n = read(fd, ptr, nbytes)) == -1)
{
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
ssize_t Write(int fd, const void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ((n = write(fd, ptr, nbytes)) == -1)
{
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
int Close(int fd)
{
int n;
if ((n = close(fd)) == -1)
perr_exit("close error");
return n;
}
/*参三: 应该读取的字节数*/
//socket 4096 readn(cfd, buf, 4096) nleft = 4096-1500
ssize_t Readn(int fd, void *vptr, size_t n)
{
size_t nleft; //usigned int 剩余未读取的字节数
ssize_t nread; //int 实际读到的字节数
char *ptr;
ptr = vptr;
nleft = n; //n 未读取字节数
while (nleft > 0)
{
if ((nread = read(fd, ptr, nleft)) < 0)
{
if (errno == EINTR) //在读取到数据以前调用被信号所中断
{
nread = 0;
}
else
{
return -1;
}
}
else if (nread == 0)
{
break;
}
nleft -= nread; //nleft = nleft - nread
ptr += nread;
}
return n - nleft;
}
ssize_t Writen(int fd, const void *vptr, size_t n)
{
size_t nleft;
ssize_t nwritten;
const char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0)
{
if ( (nwritten = write(fd, ptr, nleft)) <= 0)
{
if (nwritten < 0 && errno == EINTR)
nwritten = 0;
else
return -1;
}
nleft -= nwritten;
ptr += nwritten;
}
return n;
}
static ssize_t my_read(int fd, char *ptr)
{
static int read_cnt;
static char *read_ptr;
static char read_buf[100];
if (read_cnt <= 0) {
again:
if ( (read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) //"hello\n"
{
if (errno == EINTR)
goto again;
return -1;
}
else if (read_cnt == 0)
return 0;
read_ptr = read_buf;
}
read_cnt--;
*ptr = *read_ptr++;
return 1;
}
/*readline --- fgets*/
//传出参数 vptr
ssize_t Readline(int fd, void *vptr, size_t maxlen)
{
ssize_t n, rc;
char c, *ptr;
ptr = vptr;
for (n = 1; n < maxlen; n++)
{
if ((rc = my_read(fd, &c)) == 1) //ptr[] = hello\n
{
*ptr++ = c;
if (c == '\n')
break;
}
else if (rc == 0)
{
*ptr = 0;
return n-1;
}
else
return -1;
}
*ptr = 0;
return n;
}
#ifndef __WRAP_H_
#define __WRAP_H_
void perr_exit(const char *s);
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr);
int Bind(int fd, const struct sockaddr *sa, socklen_t salen);
int Connect(int fd, const struct sockaddr *sa, socklen_t salen);
int Listen(int fd, int backlog);
int Socket(int family, int type, int protocol);
ssize_t Read(int fd, void *ptr, size_t nbytes);
ssize_t Write(int fd, const void *ptr, size_t nbytes);
int Close(int fd);
ssize_t Readn(int fd, void *vptr, size_t n);
ssize_t Writen(int fd, const void *vptr, size_t n);
ssize_t my_read(int fd, char *ptr);
ssize_t Readline(int fd, void *vptr, size_t maxlen);
#endif
- 服务端server.c
//server.c
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <sys/wait.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/select.h>
#include "wrap.h"
#define SERV_PROT 6666
int main(int argc, char *argv[])
{
int i, j, n, nread;
int maxfd = 0;
int listenfd, connfd;
char buf[BUFSIZ];
struct sockaddr_in clie_addr, serv_addr;
socklen_t clie_addr_len;
listenfd = Socket(AF_INET, SOCK_STREAM, 0);
int opt = 1;
setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(SERV_PROT);
Bind(listen, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
Listen(listenfd, 128);
fd_set rset, allset;
maxfd = listenfd;
FD_ZERO(&allset);
FD_SET(listenfd, &allset);
while (1)
{
rset = allset;
nread = select(maxfd + 1, &rset, NULL, NULL, NULL); //每次循环都从新设置select监控信号集
if(nread < 0)
perr_exit("select error");
if (FD_ISSET(listenfd, &rset)) //说明有新的客户端连接请求
{
clie_addr_len = sizeof(clie_addr);
connfd = Accept(listenfd, (struct sockaddr *)&clie_addr, &clie_addr_len);
FD_SET(connfd, &allset); //向监控文件描述符集合allset添加新的文件描述符connfd
if (maxfd < connfd)
maxfd = connfd;
if (0 == --nread) //说明select只返回一个,并且listenfd,后续执行无须执行
continue;
}
for (i = listenfd + 1; i <= maxfd; i++)
{
if (FD_ISSET(i, &rset))
{
if ((n = Read(i, buf, sizeof(buf))) == 0) //当client关闭链接时, 服务端也关闭对应链接
{
Close(i);
FD_CLR(i, &allset); //解除select对此文件描述符的监控
}
else if(n == -1)
perr_exit("read error");
for (j = 0; j < n; ++j)
buf[j] = toupper(buf[j]);
Write(i, buf, n);
}
}
}
Close(listenfd);
return 0;
}
- 客户端:clent.c
#include <arpa/inet.h>
#include "wrap.h"
#define SERV_IP "192.168.245.139"
#define SERV_PORT 6666
int main(void)
{
int sfd, len;
struct sockaddr_in serv_addr;
char buf[BUFSIZ];
sfd = Socket(AF_INET, SOCK_STREAM, 0);
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
inet_pton(AF_INET, SERV_IP, &serv_addr.sin_addr.s_addr);
serv_addr.sin_port = htons(SERV_PORT);
Connect(sfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
while (1)
{
fgets(buf, sizeof(buf), stdin);
int r = Write(sfd, buf, strlen(buf));
printf("Write r ======== %d\n", r);
len = Read(sfd, buf, sizeof(buf));
printf("Read len ========= %d\n", len);
Write(STDOUT_FILENO, buf, len);
}
Close(sfd);
return 0;
}
- 公共头文件集程序:wrap.h、wrap.c
输出结果:
客户端:
服务端: