本文从简单到复杂，展示如何使用libevent。网上的许多例子都是只有服务器端的，本文里面客户端和服务器端都有，以飨读者。

        关于libevent编程时的一些疑问可以阅读《libevent编程疑难解答》。假如读者还想了解libevent的具体实现，可以阅读《libevent源码分析》系统文章。

        不说这么多了，直接上代码。

初等：

客户端代码：

#include<sys/types.h>  
#include<sys/socket.h>  
#include<netinet/in.h>  
#include<arpa/inet.h>  
#include<errno.h>  
#include<unistd.h>  
  
#include<stdio.h>  
#include<string.h>  
#include<stdlib.h>  
  
#include<event.h>  
#include<event2/util.h>  
  
  
  
  
int tcp_connect_server(const char* server_ip, int port);  
  
  
void cmd_msg_cb(int fd, short events, void* arg);  
void socket_read_cb(int fd, short events, void *arg);  
  
int main(int argc, char** argv)  
{  
    if( argc < 3 )  
    {  
        printf("please input 2 parameter\n");  
        return -1;  
    }  
  
  
    //两个参数依次是服务器端的IP地址、端口号  
    int sockfd = tcp_connect_server(argv[1], atoi(argv[2]));  
    if( sockfd == -1)  
    {  
        perror("tcp_connect error ");  
        return -1;  
    }  
  
    printf("connect to server successful\n");  
  
    struct event_base* base = event_base_new();  
  
    struct event *ev_sockfd = event_new(base, sockfd,  
                                        EV_READ | EV_PERSIST,  
                                        socket_read_cb, NULL);  
    event_add(ev_sockfd, NULL);  
  
    //监听终端输入事件  
    struct event* ev_cmd = event_new(base, STDIN_FILENO,  
                                      EV_READ | EV_PERSIST, cmd_msg_cb,  
                                      (void*)&sockfd);  
  
  
    event_add(ev_cmd, NULL);  
  
    event_base_dispatch(base);  
  
    printf("finished \n");  
    return 0;  
}  
  
  
  
  
  
  
void cmd_msg_cb(int fd, short events, void* arg)  
{  
    char msg[1024];  
  
    int ret = read(fd, msg, sizeof(msg));  
    if( ret <= 0 )  
    {  
        perror("read fail ");  
        exit(1);  
    }  
  
    int sockfd = *((int*)arg);  
  
    //把终端的消息发送给服务器端  
    //为了简单起见，不考虑写一半数据的情况  
    write(sockfd, msg, ret);  
}  
  
  
void socket_read_cb(int fd, short events, void *arg)  
{  
    char msg[1024];  
  
    //为了简单起见，不考虑读一半数据的情况  
    int len = read(fd, msg, sizeof(msg)-1);  
    if( len <= 0 )  
    {  
        perror("read fail ");  
        exit(1);  
    }  
  
    msg[len] = '\0';  
  
    printf("recv %s from server\n", msg);  
}  
  
  
  
typedef struct sockaddr SA;  
int tcp_connect_server(const char* server_ip, int port)  
{  
    int sockfd, status, save_errno;  
    struct sockaddr_in server_addr;  
  
    memset(&server_addr, 0, sizeof(server_addr) );  
  
    server_addr.sin_family = AF_INET;  
    server_addr.sin_port = htons(port);  
    status = inet_aton(server_ip, &server_addr.sin_addr);  
  
    if( status == 0 ) //the server_ip is not valid value  
    {  
        errno = EINVAL;  
        return -1;  
    }  
  
    sockfd = ::socket(PF_INET, SOCK_STREAM, 0);  
    if( sockfd == -1 )  
        return sockfd;  
  
  
    status = ::connect(sockfd, (SA*)&server_addr, sizeof(server_addr) );  
  
    if( status == -1 )  
    {  
        save_errno = errno;  
        ::close(sockfd);  
        errno = save_errno; //the close may be error  
        return -1;  
    }  
  
    evutil_make_socket_nonblocking(sockfd);  
  
    return sockfd;  
}  

服务器端代码：

#include<stdio.h>  
#include<string.h>  
#include<errno.h>  
  
#include<unistd.h>  
#include<event.h>  
  
  
  
void accept_cb(int fd, short events, void* arg);  
void socket_read_cb(int fd, short events, void *arg);  
  
int tcp_server_init(int port, int listen_num);  
  
int main(int argc, char** argv)  
{  
  
    int listener = tcp_server_init(9999, 10);  
    if( listener == -1 )  
    {  
        perror(" tcp_server_init error ");  
        return -1;  
    }  
  
    struct event_base* base = event_base_new();  
  
    //添加监听客户端请求连接事件  
    struct event* ev_listen = event_new(base, listener, EV_READ | EV_PERSIST,  
                                        accept_cb, base);  
    event_add(ev_listen, NULL);  
  
  
    event_base_dispatch(base);  
  
    return 0;  
}  
  
  
  
void accept_cb(int fd, short events, void* arg)  
{  
    evutil_socket_t sockfd;  
  
    struct sockaddr_in client;  
    socklen_t len = sizeof(client);  
  
    sockfd = ::accept(fd, (struct sockaddr*)&client, &len );  
    evutil_make_socket_nonblocking(sockfd);  
  
    printf("accept a client %d\n", sockfd);  
  
    struct event_base* base = (event_base*)arg;  
  
    //仅仅是为了动态创建一个event结构体  
    struct event *ev = event_new(NULL, -1, 0, NULL, NULL);  
    //将动态创建的结构体作为event的回调参数  
    event_assign(ev, base, sockfd, EV_READ | EV_PERSIST,  
                 socket_read_cb, (void*)ev);  
  
    event_add(ev, NULL);  
}  
  
  
void socket_read_cb(int fd, short events, void *arg)  
{  
    char msg[4096];  
    struct event *ev = (struct event*)arg;  
    int len = read(fd, msg, sizeof(msg) - 1);  
  
  
  
    if( len <= 0 )  
    {  
        printf("some error happen when read\n");  
        event_free(ev);  
        close(fd);  
        return ;  
    }  
  
    msg[len] = '\0';  
    printf("recv the client msg: %s", msg);  
  
    char reply_msg[4096] = "I have recvieced the msg: ";  
    strcat(reply_msg + strlen(reply_msg), msg);  
  
    write(fd, reply_msg, strlen(reply_msg) );  
}  
  
  
  
typedef struct sockaddr SA;  
int tcp_server_init(int port, int listen_num)  
{  
    int errno_save;  
    evutil_socket_t listener;  
  
    listener = ::socket(AF_INET, SOCK_STREAM, 0);  
    if( listener == -1 )  
        return -1;  
  
    //允许多次绑定同一个地址。要用在socket和bind之间  
    evutil_make_listen_socket_reuseable(listener);  
  
    struct sockaddr_in sin;  
    sin.sin_family = AF_INET;  
    sin.sin_addr.s_addr = 0;  
    sin.sin_port = htons(port);  
  
    if( ::bind(listener, (SA*)&sin, sizeof(sin)) < 0 )  
        goto error;  
  
    if( ::listen(listener, listen_num) < 0)  
        goto error;  
  
  
    //跨平台统一接口，将套接字设置为非阻塞状态  
    evutil_make_socket_nonblocking(listener);  
  
    return listener;  
  
    error:  
        errno_save = errno;  
        evutil_closesocket(listener);  
        errno = errno_save;  
  
        return -1;  
}  

中等：

客户端代码：

#include<sys/types.h>  
#include<sys/socket.h>  
#include<netinet/in.h>  
#include<arpa/inet.h>  
#include<errno.h>  
#include<unistd.h>  
  
#include<stdio.h>  
#include<string.h>  
#include<stdlib.h>  
  
#include<event.h>  
#include<event2/bufferevent.h>  
#include<event2/buffer.h>  
#include<event2/util.h>  
  
  
  
  
int tcp_connect_server(const char* server_ip, int port);  
  
  
void cmd_msg_cb(int fd, short events, void* arg);  
void server_msg_cb(struct bufferevent* bev, void* arg);  
void event_cb(struct bufferevent *bev, short event, void *arg);  
  
int main(int argc, char** argv)  
{  
    if( argc < 3 )  
    {  
        printf("please input 2 parameter\n");  
        return -1;  
    }  
  
  
    //两个参数依次是服务器端的IP地址、端口号  
    int sockfd = tcp_connect_server(argv[1], atoi(argv[2]));  
    if( sockfd == -1)  
    {  
        perror("tcp_connect error ");  
        return -1;  
    }  
  
    printf("connect to server successful\n");  
  
    struct event_base* base = event_base_new();  
  
    struct bufferevent* bev = bufferevent_socket_new(base, sockfd,  
                                                     BEV_OPT_CLOSE_ON_FREE);  
  
    //监听终端输入事件  
    struct event* ev_cmd = event_new(base, STDIN_FILENO,  
                                      EV_READ | EV_PERSIST, cmd_msg_cb,  
                                      (void*)bev);  
    event_add(ev_cmd, NULL);  
  
    //当socket关闭时会用到回调参数  
    bufferevent_setcb(bev, server_msg_cb, NULL, event_cb, (void*)ev_cmd);  
    bufferevent_enable(bev, EV_READ | EV_PERSIST);  
  
  
    event_base_dispatch(base);  
  
    printf("finished \n");  
    return 0;  
}  
  
  
  
  
  
  
void cmd_msg_cb(int fd, short events, void* arg)  
{  
    char msg[1024];  
  
    int ret = read(fd, msg, sizeof(msg));  
    if( ret < 0 )  
    {  
        perror("read fail ");  
        exit(1);  
    }  
  
    struct bufferevent* bev = (struct bufferevent*)arg;  
  
    //把终端的消息发送给服务器端  
    bufferevent_write(bev, msg, ret);  
}  
  
  
void server_msg_cb(struct bufferevent* bev, void* arg)  
{  
    char msg[1024];  
  
    size_t len = bufferevent_read(bev, msg, sizeof(msg));  
    msg[len] = '\0';  
  
    printf("recv %s from server\n", msg);  
}  
  
  
void event_cb(struct bufferevent *bev, short event, void *arg)  
{  
  
    if (event & BEV_EVENT_EOF)  
        printf("connection closed\n");  
    else if (event & BEV_EVENT_ERROR)  
        printf("some other error\n");  
  
    //这将自动close套接字和free读写缓冲区  
    bufferevent_free(bev);  
  
    struct event *ev = (struct event*)arg;  
    //因为socket已经没有，所以这个event也没有存在的必要了  
    event_free(ev);  
}  
  
  
typedef struct sockaddr SA;  
int tcp_connect_server(const char* server_ip, int port)  
{  
    int sockfd, status, save_errno;  
    struct sockaddr_in server_addr;  
  
    memset(&server_addr, 0, sizeof(server_addr) );  
  
    server_addr.sin_family = AF_INET;  
    server_addr.sin_port = htons(port);  
    status = inet_aton(server_ip, &server_addr.sin_addr);  
  
    if( status == 0 ) //the server_ip is not valid value  
    {  
        errno = EINVAL;  
        return -1;  
    }  
  
    sockfd = ::socket(PF_INET, SOCK_STREAM, 0);  
    if( sockfd == -1 )  
        return sockfd;  
  
  
    status = ::connect(sockfd, (SA*)&server_addr, sizeof(server_addr) );  
  
    if( status == -1 )  
    {  
        save_errno = errno;  
        ::close(sockfd);  
        errno = save_errno; //the close may be error  
        return -1;  
    }  
  
    evutil_make_socket_nonblocking(sockfd);  
  
    return sockfd;  
}  

服务器端代码：

#include<stdio.h>  
#include<string.h>  
#include<errno.h>  
  
#include<event.h>  
#include<event2/bufferevent.h>  
  
  
  
void accept_cb(int fd, short events, void* arg);  
void socket_read_cb(bufferevent* bev, void* arg);  
void event_cb(struct bufferevent *bev, short event, void *arg);  
int tcp_server_init(int port, int listen_num);  
  
int main(int argc, char** argv)  
{  
  
    int listener = tcp_server_init(9999, 10);  
    if( listener == -1 )  
    {  
        perror(" tcp_server_init error ");  
        return -1;  
    }  
  
    struct event_base* base = event_base_new();  
  
    //添加监听客户端请求连接事件  
    struct event* ev_listen = event_new(base, listener, EV_READ | EV_PERSIST,  
                                        accept_cb, base);  
    event_add(ev_listen, NULL);  
  
  
    event_base_dispatch(base);  
    event_base_free(base);  
  
  
    return 0;  
}  
  
  
  
void accept_cb(int fd, short events, void* arg)  
{  
    evutil_socket_t sockfd;  
  
    struct sockaddr_in client;  
    socklen_t len = sizeof(client);  
  
    sockfd = ::accept(fd, (struct sockaddr*)&client, &len );  
    evutil_make_socket_nonblocking(sockfd);  
  
    printf("accept a client %d\n", sockfd);  
  
    struct event_base* base = (event_base*)arg;  
  
    bufferevent* bev = bufferevent_socket_new(base, sockfd, BEV_OPT_CLOSE_ON_FREE);  
    bufferevent_setcb(bev, socket_read_cb, NULL, event_cb, arg);  
  
    bufferevent_enable(bev, EV_READ | EV_PERSIST);  
}  
  
  
  
void socket_read_cb(bufferevent* bev, void* arg)  
{  
    char msg[4096];  
  
    size_t len = bufferevent_read(bev, msg, sizeof(msg));  
  
    msg[len] = '\0';  
    printf("recv the client msg: %s", msg);  
  
  
    char reply_msg[4096] = "I have recvieced the msg: ";  
  
    strcat(reply_msg + strlen(reply_msg), msg);  
    bufferevent_write(bev, reply_msg, strlen(reply_msg));  
}  
  
  
  
void event_cb(struct bufferevent *bev, short event, void *arg)  
{  
  
    if (event & BEV_EVENT_EOF)  
        printf("connection closed\n");  
    else if (event & BEV_EVENT_ERROR)  
        printf("some other error\n");  
  
    //这将自动close套接字和free读写缓冲区  
    bufferevent_free(bev);  
}  
  
  
typedef struct sockaddr SA;  
int tcp_server_init(int port, int listen_num)  
{  
    int errno_save;  
    evutil_socket_t listener;  
  
    listener = ::socket(AF_INET, SOCK_STREAM, 0);  
    if( listener == -1 )  
        return -1;  
  
    //允许多次绑定同一个地址。要用在socket和bind之间  
    evutil_make_listen_socket_reuseable(listener);  
  
    struct sockaddr_in sin;  
    sin.sin_family = AF_INET;  
    sin.sin_addr.s_addr = 0;  
    sin.sin_port = htons(port);  
  
    if( ::bind(listener, (SA*)&sin, sizeof(sin)) < 0 )  
        goto error;  
  
    if( ::listen(listener, listen_num) < 0)  
        goto error;  
  
  
    //跨平台统一接口，将套接字设置为非阻塞状态  
    evutil_make_socket_nonblocking(listener);  
  
    return listener;  
  
    error:  
        errno_save = errno;  
        evutil_closesocket(listener);  
        errno = errno_save;  
  
        return -1;  
}  

高等：

客户端代码：

#include<sys/types.h>  
#include<sys/socket.h>  
#include<netinet/in.h>  
#include<arpa/inet.h>  
#include<errno.h>  
#include<unistd.h>  
  
#include<stdio.h>  
#include<string.h>  
#include<stdlib.h>  
  
#include<event.h>  
#include<event2/bufferevent.h>  
#include<event2/buffer.h>  
#include<event2/util.h>  
  
  
  
  
int tcp_connect_server(const char* server_ip, int port);  
  
  
void cmd_msg_cb(int fd, short events, void* arg);  
void server_msg_cb(struct bufferevent* bev, void* arg);  
void event_cb(struct bufferevent *bev, short event, void *arg);  
  
int main(int argc, char** argv)  
{  
    if( argc < 3 )  
    {  
        //两个参数依次是服务器端的IP地址、端口号  
        printf("please input 2 parameter\n");  
        return -1;  
    }  
  
    struct event_base *base = event_base_new();  
  
    struct bufferevent* bev = bufferevent_socket_new(base, -1,  
                                                     BEV_OPT_CLOSE_ON_FREE);  
  
    //监听终端输入事件  
    struct event* ev_cmd = event_new(base, STDIN_FILENO,  
                                     EV_READ | EV_PERSIST,  
                                     cmd_msg_cb, (void*)bev);  
  
  
    event_add(ev_cmd, NULL);  
  
    struct sockaddr_in server_addr;  
  
    memset(&server_addr, 0, sizeof(server_addr) );  
  
    server_addr.sin_family = AF_INET;  
    server_addr.sin_port = htons(atoi(argv[2]));  
    inet_aton(argv[1], &server_addr.sin_addr);  
  
    bufferevent_socket_connect(bev, (struct sockaddr *)&server_addr,  
                               sizeof(server_addr));  
  
  
    bufferevent_setcb(bev, server_msg_cb, NULL, event_cb, (void*)ev_cmd);  
    bufferevent_enable(bev, EV_READ | EV_PERSIST);  
  
  
  
    event_base_dispatch(base);  
  
    printf("finished \n");  
    return 0;  
}  
  
  
  
  
  
void cmd_msg_cb(int fd, short events, void* arg)  
{  
    char msg[1024];  
  
    int ret = read(fd, msg, sizeof(msg));  
    if( ret < 0 )  
    {  
        perror("read fail ");  
        exit(1);  
    }  
  
    struct bufferevent* bev = (struct bufferevent*)arg;  
  
    //把终端的消息发送给服务器端  
    bufferevent_write(bev, msg, ret);  
}  
  
  
void server_msg_cb(struct bufferevent* bev, void* arg)  
{  
    char msg[1024];  
  
    size_t len = bufferevent_read(bev, msg, sizeof(msg));  
    msg[len] = '\0';  
  
    printf("recv %s from server\n", msg);  
}  
  
  
void event_cb(struct bufferevent *bev, short event, void *arg)  
{  
  
    if (event & BEV_EVENT_EOF)  
        printf("connection closed\n");  
    else if (event & BEV_EVENT_ERROR)  
        printf("some other error\n");  
    else if( event & BEV_EVENT_CONNECTED)  
    {  
        printf("the client has connected to server\n");  
        return ;  
    }  
  
    //这将自动close套接字和free读写缓冲区  
    bufferevent_free(bev);  
  
    struct event *ev = (struct event*)arg;  
    event_free(ev);  
}  

服务器端代码：

#include<netinet/in.h>    
#include<sys/socket.h>    
#include<unistd.h>    
    
#include<stdio.h>    
#include<string.h>    
    
#include<event.h>    
#include<listener.h>    
#include<bufferevent.h>    
#include<thread.h>    
    
    
void listener_cb(evconnlistener *listener, evutil_socket_t fd,    
                 struct sockaddr *sock, int socklen, void *arg);    
    
void socket_read_cb(bufferevent *bev, void *arg);    
void socket_event_cb(bufferevent *bev, short events, void *arg);    
    
int main()    
{    
    //evthread_use_pthreads();//enable threads    
    
    struct sockaddr_in sin;    
    memset(&sin, 0, sizeof(struct sockaddr_in));    
    sin.sin_family = AF_INET;    
    sin.sin_port = htons(9999);    
    
    event_base *base = event_base_new();    
    evconnlistener *listener    
            = evconnlistener_new_bind(base, listener_cb, base,    
                                      LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE,    
                                      10, (struct sockaddr*)&sin,    
                                      sizeof(struct sockaddr_in));    
    
    event_base_dispatch(base);    
    
    evconnlistener_free(listener);    
    event_base_free(base);    
    
    return 0;    
}    
    
    
//一个新客户端连接上服务器了    
//当此函数被调用时，libevent已经帮我们accept了这个客户端。该客户端的  
//文件描述符为fd  
void listener_cb(evconnlistener *listener, evutil_socket_t fd,    
                 struct sockaddr *sock, int socklen, void *arg)    
{    
    printf("accept a client %d\n", fd);    
    
    event_base *base = (event_base*)arg;    
    
    //为这个客户端分配一个bufferevent    
    bufferevent *bev =  bufferevent_socket_new(base, fd,    
                                               BEV_OPT_CLOSE_ON_FREE);    
    
    bufferevent_setcb(bev, socket_read_cb, NULL, socket_event_cb, NULL);    
    bufferevent_enable(bev, EV_READ | EV_PERSIST);    
}    
    
    
void socket_read_cb(bufferevent *bev, void *arg)    
{    
    char msg[4096];    
    
    size_t len = bufferevent_read(bev, msg, sizeof(msg)-1 );    
    
    msg[len] = '\0';    
    printf("server read the data %s\n", msg);    
    
    char reply[] = "I has read your data";    
    bufferevent_write(bev, reply, strlen(reply) );    
}    
    
    
void socket_event_cb(bufferevent *bev, short events, void *arg)    
{    
    if (events & BEV_EVENT_EOF)    
        printf("connection closed\n");    
    else if (events & BEV_EVENT_ERROR)    
        printf("some other error\n");    
    
    //这将自动close套接字和free读写缓冲区    
    bufferevent_free(bev);    
}