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我在服务器端使用 C 为聊天客户端编写了以下代码。但是，在 while 循环中，我需要检查客户端是否已退出程序，即与客户端的连接是否丢失。请告诉我如何编写这样的代码。

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <time.h>
int main()
{
int sock, connected, bytes_recieved , true = 1, pid;  
char send_data [1024] , recv_data[1024];     
struct sockaddr_in server_addr,client_addr;    
int sin_size;
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
    perror("Socket");
    exit(1);
}
if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&true,sizeof(int)) == -1)
{
    perror("Setsockopt");
    exit(1);
}
server_addr.sin_family = AF_INET;         
server_addr.sin_port = htons(3128);     
server_addr.sin_addr.s_addr = INADDR_ANY; 
bzero(&(server_addr.sin_zero),8); 
if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
{
    perror("Unable to bind");
    exit(1);
}
if (listen(sock, 5) == -1)
{
    perror("Listen");
    exit(1);
}
printf("\nTCPServer Waiting for client on port 3128");
fflush(stdout);
FILE *log;
log = fopen("time.log", "a");
time_t t;
while(1)
{  
    sin_size = sizeof(struct sockaddr_in);
    connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size);
    printf("\n I got a connection from (%s , %d)", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
    fflush(stdout);           
    int pid=fork();
    while(1)
    {       
        if(pid == 0)
        {
            usleep(1000000);
            time(&t);
            send(connected, ctime(&t),30, 0);
        }
        else
        {
            bytes_recieved = recv(connected,recv_data,1024,0);
            recv_data[bytes_recieved] = '\0';
            fputs(recv_data, log);
            fputs("Time: ", log);
            time(&t);
            fputs(ctime(&t), log);
        }
        fflush(log);
    }   
    }   
fclose(log);
close(sock);
return 0;
}

请帮忙。

现在我修改了这样的代码：

while(1)
{       
    if(pid == 0)
    {
        usleep(1000000); 
        time(&t);
        send(connected, ctime(&t),30, 0);
    }
    else
    {
        bytes_recieved = recv(connected,recv_data,1024,0);
        recv_data[bytes_recieved] = '\0';
        fputs(recv_data, log);
        fputs("Time: ", log);
        time(&t);
        fputs(ctime(&t), log);
    }
    fflush(stdout);
    fflush(log);
    fclose(log);
    if(bytes_recieved == 0 || bytes_recieved == -1)
    {
        close(sock); goto connct;}
    }   
}
close(sock);
return 0;

在编译时，它运行良好，但在运行时，它给出以下错误输出：

*** glibc detected *** ./server: double free or corruption (!prev): 0x09936008 ***
======= Backtrace: =========
/lib/i686/cmov/libc.so.6(+0x6b381)[0xb7659381]
/lib/i686/cmov/libc.so.6(+0x6cbd8)[0xb765abd8]
/lib/i686/cmov/libc.so.6(cfree+0x6d)[0xb765dcbd]
/lib/i686/cmov/libc.so.6(fclose+0x14a)[0xb764982a]
./server[0x8048c21]
/lib/i686/cmov/libc.so.6(__libc_start_main+0xe6)[0xb7604ca6]
./server[0x8048861]
======= Memory map: ========
08048000-08049000 r-xp 00000000 08:01 133298     /home/harikrishnan/server/server
08049000-0804a000 rw-p 00000000 08:01 133298     /home/harikrishnan/server/server
09936000-09957000 rw-p 00000000 00:00 0          [heap]
b7400000-b7421000 rw-p 00000000 00:00 0 
b7421000-b7500000 ---p 00000000 00:00 0 
b75bf000-b75dc000 r-xp 00000000 08:01 3653635    /lib/libgcc_s.so.1
b75dc000-b75dd000 rw-p 0001c000 08:01 3653635    /lib/libgcc_s.so.1
b75ed000-b75ee000 rw-p 00000000 00:00 0 
b75ee000-b772e000 r-xp 00000000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b772e000-b772f000 ---p 00140000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b772f000-b7731000 r--p 00140000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b7731000-b7732000 rw-p 00142000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b7732000-b7735000 rw-p 00000000 00:00 0 
b7744000-b7747000 rw-p 00000000 00:00 0 
b7747000-b7748000 r-xp 00000000 00:00 0          [vdso]
b7748000-b7763000 r-xp 00000000 08:01 3654097    /lib/ld-2.11.3.so
b7763000-b7764000 r--p 0001b000 08:01 3654097    /lib/ld-2.11.3.so
b7764000-b7765000 rw-p 0001c000 08:01 3654097    /lib/ld-2.11.3.so
bfd94000-bfda9000 rw-p 00000000 00:00 0          [stack]
*** glibc detected *** ./server: double free or corruption (!prev): 0x09936008 ***
======= Backtrace: =========
/lib/i686/cmov/libc.so.6(+0x6b381)[0xb7659381]
/lib/i686/cmov/libc.so.6(+0x6cbd8)[0xb765abd8]
/lib/i686/cmov/libc.so.6(cfree+0x6d)[0xb765dcbd]
/lib/i686/cmov/libc.so.6(fclose+0x14a)[0xb764982a]
./server[0x8048c21]
/lib/i686/cmov/libc.so.6(__libc_start_main+0xe6)[0xb7604ca6]
./server[0x8048861]
======= Memory map: ========
08048000-08049000 r-xp 00000000 08:01 133298     /home/harikrishnan/server/server
08049000-0804a000 rw-p 00000000 08:01 133298     /home/harikrishnan/server/server
09936000-09957000 rw-p 00000000 00:00 0          [heap]
b7400000-b7421000 rw-p 00000000 00:00 0 
b7421000-b7500000 ---p 00000000 00:00 0 
b75bf000-b75dc000 r-xp 00000000 08:01 3653635    /lib/libgcc_s.so.1
b75dc000-b75dd000 rw-p 0001c000 08:01 3653635    /lib/libgcc_s.so.1
b75ed000-b75ee000 rw-p 00000000 00:00 0 
b75ee000-b772e000 r-xp 00000000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b772e000-b772f000 ---p 00140000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b772f000-b7731000 r--p 00140000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b7731000-b7732000 rw-p 00142000 08:01 3670051    /lib/i686/cmov/libc-2.11.3.so
b7732000-b7735000 rw-p 00000000 00:00 0 
b7744000-b7747000 rw-p 00000000 00:00 0 
b7747000-b7748000 r-xp 00000000 00:00 0          [vdso]
b7748000-b7763000 r-xp 00000000 08:01 3654097    /lib/ld-2.11.3.so
b7763000-b7764000 r--p 0001b000 08:01 3654097    /lib/ld-2.11.3.so
b7764000-b7765000 rw-p 0001c000 08:01 3654097    /lib/ld-2.11.3.so
bfd94000-bfda9000 rw-p 00000000 00:00 0          [stack]
Aborted

知道实际问题是什么吗？

4

3 回答 3

3

recv()0客户端关闭连接后将立即返回。-1如果尝试从套接字获取数据时出现任何错误，将返回。

有关更多信息，请参见手册页。

所以将您的代码更改为

   int conn_closed = 0;

   bytes_recieved = recv(connected,recv_data,1024,0);
   switch (bytes_recieved) {
   case 0:
         /* connection closed by client */
         close(connected);
         conn_closed = 1;
         break;
   case -1:
         /* error on socket */
         /* TODO: insert error handling code */
         if (errno == EAGAIN || errno == EINTR) {
            /* safe to retry */
            conn_closed = 0;
         } else {
            close(connected)
            conn_closed = 1;
         }
         break;
   default:
        recv_data[bytes_recieved] = '\0';
        fputs(recv_data, log);
        fputs("Time: ", log);
        time(&t);
        fputs(ctime(&t), log);
        conn_closed = 0;
        break;
   }
   /* break out of the loop if conn_closed */
   if (conn_closed)
       break;

并且不要忘记检查 的返回值send()，以查看发送数据时是否发生错误。

EAGAIN更新：为和添加错误处理代码EINTR。

第二次更新：

为了完整起见，这是您应该添加的发送代码

if (send(connected, ctime(&t),30, 0) == -1)
{
    if (errno == EAGAIN || errno == EINTR) {
       /* retry to send */
    }
    close(connected);
    break;
}
于 2012-05-16T11:15:10.343 回答
0

如果 send 返回 SOCKET_ERROR 表示套接字关闭或连接丢失

所以就这样做

if (send(connected, ctime(&t),30, 0) == SOCKET_ERROR)
 {
   // blablabla
 }
于 2012-05-16T11:15:02.313 回答
0

在你的情况下，一个小建议，而不是给出一个“if”条件来检查连接，而是在“while”中做同样的事情，而不是“while(1)”，给出条件。

于 2012-05-16T13:27:53.703 回答