int yes = 1;
setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &yes, sizeof(yes));

#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<netinet/tcp.h>
#include<sys/socket.h>
#include<sys/wait.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<sys/time.h>int main(int argc, char **argv)
{struct sockaddr_in s_addr;int sock;int addr_len;int len;char buff[128];int yes;//UDP 创建socketif((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1){perror("socket");exit(EXIT_FAILURE);}else{printf("create socket.\n\r");}//设置socket为可发送广播消息yes = 1;setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &yes, sizeof(yes));s_addr.sin_family = AF_INET;s_addr.sin_port = htons(7838);if(argv[1]){s_addr.sin_addr.s_addr = inet_addr(argv[1]); //参数1 广播地址
    }    else{printf("input sever ip!\n");exit(0);}addr_len = sizeof(s_addr);strcpy(buff, "hello message");//发送消息len = sendto(sock, buff, strlen(buff), 0, (struct sockaddr *)&s_addr, addr_len);if(len < 0){printf("\n\rsend error.\n\r");exit(EXIT_FAILURE);}printf("send success.\n\r");return 0;
}

#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<netinet/tcp.h>
#include<sys/socket.h>
#include<sys/wait.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<sys/time.h>int main(int argc, char **argv)
{struct sockaddr_in s_addr;struct sockaddr_in c_addr;int sock;socklen_t addr_len;int len;char buff[128];//创建socket UDPif((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1){perror("socket");exit(EXIT_FAILURE);}else{printf("create socket.\n\r");}memset(&s_addr, 0, sizeof(struct sockaddr_in));s_addr.sin_family = AF_INET;s_addr.sin_port = htons(7838);s_addr.sin_addr.s_addr = INADDR_ANY;//绑定IP地址if((bind(sock, (struct sockaddr *)&s_addr, sizeof(s_addr))) == -1){perror("bind");exit(EXIT_FAILURE);}else{printf("bind address to socket.\n\r");}addr_len = sizeof(c_addr);while(1){//阻塞方式接收数据len = recvfrom(sock, buff, sizeof(buff) - 1, 0, (struct sockaddr *)&c_addr, &addr_len);if(len < 0){perror("recvfrom");exit(EXIT_FAILURE);}buff[len] = '\0';printf("recive come from %s:%d message:%s\n\r", inet_ntoa(c_addr.sin_addr), ntohs(c_addr.sin_port), buff);}return 0;
}