listen

listen（等待连接）

相关函数：socket，bind，accept，connect

表头文件：#include <sys/socket.h>

定义函数：int listen(int s, int backlog);

函数说明：listen()用来等待参数s的socket连线。参数backlog指定同时能处理的最大连接要求，如果连接数目达此上限则client端将收到ECONNREFUSED的错误。Listen()并未开始接收连线，只是设置socket为listen模式，真正接收client端连线的是accept()。通常listen()会在socket()，bind()之后调用，接着才调用accept()。

返回值：成功则返回0，失败返回-1，错误原因存于errno

附加说明：listen()只适用SOCK_STREAM或SOCK_SEQPACKET的socket类型。如果socket为AF_INET则参数backlog最大值可设至128。

错误代码：EBADF 参数sockfd非合法socket处理代码 EACCESS 权限不足 EOPNOTSUPP 指定的socket并未支援listen模式。

范例：

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#define PORT 1234 #define MAXSOCKFD 10
main()
{
    int sockfd, newsockfd, is_connected[MAXSOCKFD], fd;
    struct sockaddr_in addr;
    int addr_len = sizeof(
    struct sockaddr_in); fd_set readfds; char buffer[256]; char msg[] = "Welcome to server!"; if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        perror("socket");
        exit(1);
    }
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(PORT);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(sockfd, &addr, sizeof(addr)) < 0)
{
    perror("connect");
    exit(1);
}
if (listen(sockfd, 3) < 0)
{
    perror("listen");
    exit(1);
}
for (fd = 0; fd < MAXSOCKFD; fd++) is_connected[fd] = 0; while (1)
{
    FD_ZERO(&readfds);
    FD_SET(sockfd, &readfds);
    for (fd = 0; fd < MAXSOCKFD; fd++) if (is_connected[fd]) FD_SET(fd, &readfds); if (!select(MAXSOCKFD, &readfds, NULL, NULL, NULL)) continue; for (fd = 0; fd < MAXSOCKFD; fd++) if (FD_ISSET(fd, &readfds))
    {
        if (sockfd == fd)
        {
            if ((newsockfd = accept(sockfd, &addr, &addr_len)) < 0) perror("accept");
            write(newsockfd, msg, sizeof(msg));
            is_connected[newsockfd] = 1;
            printf("cnnect from %s\n", inet_ntoa(addr.sin_addr));
        }
    else
    {
        bzero(buffer, sizeof(buffer));
        if (read(fd, buffer, sizeof(buffer)) <= 0)
        {
            printf("connect closed.\n");
            is_connected[fd] = 0;
            close(fd);
        }
    else printf("%s", buffer);
}
}
}
}

执行： $

./listen

connect

from

127.0.0.1

hi

I

am

client

connected

closed.