UDP客户端，也就是首先主动发送数据的一方。

UDP服务器，也就是首先等待接收数据的一方。

涉及的函数

ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags,
                        struct sockaddr *src_addr, socklen_t *addrlen);

ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,
                      const struct sockaddr *dest_addr, socklen_t addrlen);

 udp客户端测试

测试代码 

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>
#include <signal.h>
#include <fcntl.h>
#include <time.h>

#define _DEBUG_INFO
#ifdef _DEBUG_INFO
#define DEBUG_INFO(format, ...) printf("%s:%s:%d -- "format"\n" \
,__FILE__,__func__,__LINE__ \
, ##__VA_ARGS__)
#else
#define DEBUG_INFO(format, ...)
#endif

int main(int argc, char *argv[])
{
    int client_socket;
    client_socket = socket(AF_INET,SOCK_DGRAM,0);
    DEBUG_INFO("client_socket = %d",client_socket);

    struct sockaddr_in server_addr;
    server_addr.sin_port = htons(6600);
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr("192.168.0.5");
    char buf[100];
    snprintf(buf,sizeof(buf),"time=%d",time(NULL));

    DEBUG_INFO("server_addr %s:%d on socket %d\n",
                           inet_ntoa(server_addr.sin_addr),
                           htons(server_addr.sin_port),
                           client_socket);

    int send_len = sendto(client_socket,buf,strlen(buf),0,&server_addr,sizeof(server_addr));
    memset(buf,0,sizeof(buf));
    DEBUG_INFO("sendto %s:%d \n",
                           inet_ntoa(server_addr.sin_addr),
                           htons(server_addr.sin_port));
    int read_len = recvfrom(client_socket,buf,sizeof(buf),0,&server_addr,sizeof(server_addr));
    DEBUG_INFO("recvfrom %s:%d  -- %s\n",
                           inet_ntoa(server_addr.sin_addr),
                           htons(server_addr.sin_port),
                           buf);
    
    sleep(5);
    return 0;
}

UDP接收端(服务器)

执行代码：

实验解析 

UDP服务端 

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>
#include <signal.h>
#include <fcntl.h>

// #define _DEBUG_INFO
#ifdef _DEBUG_INFO
#define DEBUG_INFO(format, ...) printf("%s:%s:%d -- "format"\n" \
,__FILE__,__func__,__LINE__ \
, ##__VA_ARGS__)
#else
#define DEBUG_INFO(format, ...)
#endif

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>
#include <signal.h>
#include <fcntl.h>
#include <time.h>

#define _DEBUG_INFO
#ifdef _DEBUG_INFO
#define DEBUG_INFO(format, ...) printf("%s:%s:%d -- "format"\n" \
,__FILE__,__func__,__LINE__ \
, ##__VA_ARGS__)
#else
#define DEBUG_INFO(format, ...)
#endif

int main(int argc, char *argv[])
{
    int server_socket;
    int res = 0;
    int on = 1;
    server_socket = socket(AF_INET,SOCK_DGRAM,0);
    DEBUG_INFO("server_socket = %d",server_socket);

    if(setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR,&on,sizeof(on)) < 0){
        perror("setsockopt");
        exit(-1);
    }

    struct sockaddr_in server_addr;
    server_addr.sin_port = htons(6600);
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = inet_addr("192.168.0.11");

    res = bind(server_socket,(const struct sockaddr *)&server_addr,sizeof(server_addr));
    if(res == -1){
        perror("bind");
        return -1;
    }
    int len = 0;
    char buf[100];
    socklen_t addrlen;
    struct sockaddr_in client_server;
    while(1){
        memset(buf,0,sizeof(buf));
        memcpy(&client_server,&server_addr,sizeof(client_server));
        addrlen = sizeof(client_server);
        recvfrom(server_socket,buf,sizeof(buf),0,&client_server,&addrlen);
        DEBUG_INFO("buf = %s",buf);
        DEBUG_INFO("recfrom %s:%d  -- %s\n",
                           inet_ntoa(client_server.sin_addr),
                           htons(client_server.sin_port),
                           buf);
        addrlen = sizeof(client_server);
        sendto(server_socket,buf,strlen(buf),0,&client_server,addrlen);
    }
    
    sleep(5);
    return 0;
}

修改客户端中的IP地址为192.168.0.11，也就是虚拟机的IP地址

 实验解析：

小结