#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>

static bool stop = false;
static void handle_term( int sig )
{
    stop = true;
}

int main( int argc, char* argv[] )
{
    signal( SIGTERM, handle_term );

    if( argc <= 3 )
    {
        printf( "usage: %s ip_address port_number backlog\n", basename( argv[0] ) );
        return 1;
    }
    const char* ip = argv[1];
    int port = atoi( argv[2] );
    int backlog = atoi( argv[3] );

    // 1.创建socket
    // int domanin: 协议族： PF_UNIX: UNIX本地域协议族 PF_INET: TCP/IPv4协议族 PF_INET6: TCP/IPv6协议族
    // int type: SOCK_STREAM(流服务)：TCP SOCK_UGRAM(数据报):UDP
    int sock = socket( PF_INET, SOCK_STREAM, 0 );
    assert( sock >= 0 );

    // 2.确定socket地址
    struct sockaddr_in address;
    bzero( &address, sizeof( address ) );
    // 地址族：AF_UNIX: UNIX本地域协议族 AF_INET: TCP/IPv4协议族 AF_INET6: TCP/IPv6协议族
    address.sin_family = AF_INET;
    inet_pton( AF_INET, ip, &address.sin_addr );
    // 转换为网络字节序：大段
    address.sin_port = htons( port );

    // 3.命名socket
    int ret = bind( sock, ( struct sockaddr* )&address, sizeof( address ) );
    assert( ret != -1 );

    // 4.监听socket
    ret = listen( sock, backlog );
    assert( ret != -1 );

    while ( ! stop )
    {
        sleep( 1 );
    }

    close( sock );
    return 0;
}

执行

./5-3testlisten 10.120.225.64 12345 5 # 监听12345 backlog使用5
telnet 10.120.225.64 12345 & 
netstat -nt | grep 12345

结果

netstat -nt | grep 12345
tcp        0      0 10.120.225.64:12345     10.143.44.169:63208     SYN_RECV    
tcp        0      0 10.120.225.64:12345     10.120.225.64:52750     SYN_RECV    
tcp        0      0 10.120.225.64:52750     10.120.225.64:12345     ESTABLISHED 
tcp        0      0 10.120.225.64:12345     10.120.225.64:52746     ESTABLISHED 
tcp        0      0 10.120.225.64:52746     10.120.225.64:12345     ESTABLISHED 
tcp        0      0 10.120.225.64:52748     10.120.225.64:12345     ESTABLISHED   
tcp        0      0 10.120.225.64:52745     10.120.225.64:12345     ESTABLISHED 
tcp        0      0 10.120.225.64:12345     10.120.225.64:52745     ESTABLISHED