linux socket怎么检测断开

我想通过recv和send的返回值来判断是否连接异常，但是不成功，下面是我的测试代码，连接成功后如果我断开客户端，那么服务端不会打印错误信息而是等待几秒后直接终止；如果断开服务端，客户端的recv不再阻塞，而且返回值一直是0,请高手指点。

C/C++ code//服务端

#include <stdio.h>

#include <stdlib.h>

#include <errno.h>

#include <string.h>

#include <sys/types.h>

#include <netinet/in.h>

#include <sys/socket.h>

#include <sys/wait.h>

#define MYPORT 3490 /*定义用户连接端口*/

#define BACKLOG 10 /*多少等待连接控制*/

int main(int argc, char *argv[])

{

int sockfd, new_fd/* listen on sock_fd, new connection on new_fd*/

struct sockaddr_in my_addr/* my address information */

struct sockaddr_in their_addr/* connector's address information */

int sin_size

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)

{

perror("socket")

exit(1)

}

int opt = 1

int len = sizeof(opt)

setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &opt, len)

my_addr.sin_family = AF_INET/* host byte order */

my_addr.sin_port = htons(MYPORT)/* short, network byte order */

my_addr.sin_addr.s_addr = INADDR_ANY/* auto-fill with my IP */

bzero(&(my_addr.sin_zero),0)/* zero the rest of the struct */

if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr))== -1)

{

perror("bind")

exit(1)

}

if (listen(sockfd, BACKLOG) == -1) {

perror("listen")

exit(1)

}

while(1) { /* main accept() loop */

sin_size = sizeof(struct sockaddr_in)

printf("while\n")

if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size)) == -1)

{

perror("accept")

continue

}

printf("server: got connection from %s\n", inet_ntoa(their_addr.sin_addr))

while(1)

{

usleep(10000000)

if (send(new_fd, "Hello, world!\n", 14, 0) == -1)

perror("send")

}

close(new_fd)

exit(0)

}

return 0

}

C/C++ code//客户端

#include <stdio.h>

#include <stdlib.h>

#include <errno.h>

#include <string.h>

#include <sys/types.h>

#include <netinet/in.h>

#include <sys/socket.h>

#include <sys/wait.h>

#include <netdb.h>

#define PORT 3490 /* 客户机连接远程主机的端口 */

#define MAXDATASIZE 100 /* 每次可以接收的最大字节 */

int main(int argc, char *argv[])

{

int sockfd, numbytes

char buf[MAXDATASIZE]

struct hostent *he

struct sockaddr_in their_addr/* connector's address information */

if (argc != 2)

{

fprintf(stderr,"usage: client hostname\n")

exit(1)

}

if ((he=gethostbyname(argv[1])) == NULL)

{ /* get the host info */

herror("gethostbyname")

exit(1)

}

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)

{

perror("socket")

exit(1)

}

their_addr.sin_family = AF_INET/* host byte order */

their_addr.sin_port = htons(PORT)/* short, network byte order */

their_addr.sin_addr = *((struct in_addr *)(he->h_addr))

bzero(&(their_addr.sin_zero),0)/* zero the rest of the struct */

if (connect(sockfd, (struct sockaddr *)&their_addr,sizeof(struct sockaddr)) == -1)

{

perror("connect")

exit(1)

}

while(1)

{

printf("receiving......\n")

if ((numbytes=recv(sockfd, buf, MAXDATASIZE, 0)) == -1)

{

perror("recv")

exit(1)

}

buf[numbytes] = '\0'

printf("Received: %s\n",buf)

}

close(sockfd)

return 0

}

另外，在网上看到一种利用TCP协议栈中的KeepAlive探测的方法，下面是我从网上找的用的比较多的一段代码，这里应该只是设置了一些属性参数，但不知具体怎样在通信中检测断开，请高手赐教。

C/C++ code#include

……

////KeepAlive实现

//下面代码要求有ACE,如果没有包含ACE,则请把用到的ACE函数改成linux相应的接口

int keepAlive = 1//设定KeepAlive

int keepIdle = 5//开始首次KeepAlive探测前的TCP空闭时间

int keepInterval = 5//两次KeepAlive探测间的时间间隔

int keepCount = 3//判定断开前的KeepAlive探测次数

if(setsockopt(s,SOL_SOCKET,SO_KEEPALIVE,(void*)&keepAlive,sizeof(keepAlive)) == -1)

{

ACE_DEBUG ((LM_INFO,

ACE_TEXT ("(%P|%t) setsockopt SO_KEEPALIVE error!\n")))

}

if(setsockopt(s,SOL_TCP,TCP_KEEPIDLE,(void *)&keepIdle,sizeof(keepIdle)) == -1)

{

ACE_DEBUG ((LM_INFO,

ACE_TEXT ("(%P|%t) setsockopt TCP_KEEPIDLE error!\n")))

}

if(setsockopt(s,SOL_TCP,TCP_KEEPINTVL,(void *)&keepInterval,sizeof(keepInterval)) == -1)

{

ACE_DEBUG ((LM_INFO,

ACE_TEXT ("(%P|%t) setsockopt TCP_KEEPINTVL error!\n")))

}

if(setsockopt(s,SOL_TCP,TCP_KEEPCNT,(void *)&keepCount,sizeof(keepCount)) == -1)

{

ACE_DEBUG ((LM_INFO,

ACE_TEXT ("(%P|%t)setsockopt TCP_KEEPCNT error!\n")))

}

tcp连接本身就是有状态的...何必要依靠发送数据来确定...

第一,不管服务器还是客户端断开连接,另一端必定会收到socket连接断开的异常

第二,在socket发送数据前,可以检查 socket.isConnected() 来判断连接是否存在

第三,假设服务器没有开启,connect动作就不应该会执行下去,直接就抛错了

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