C语言socket UDP广播的发送和接收示例

server.c通过UDP广播的形式向网段的指定端口发送广播信息
client.c绑定到指定端口，并阻塞接收广播内容然后打印出来
程序非常简单，不过有一点需要注意，那就是setsockopt()函数的使用。使用不当很可能会出问题。通过SO_REUSEADDR选项可以实现端口号的重用，SO_BROADCAST选项表示要发送的是广播信息，optval参数要给合理的初始值（这里是1），否则很可能会发送失败
(sendto() permission denied)
发送广播的程序：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/wait.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<errno.h>
int main(){
char msg[128] = "I am broadCast message from server!";
int brdcFd;
if((brdcFd = socket(PF_INET, SOCK_DGRAM, 0)) == -1){
printf("socket fail\n");
return -1;
}
int optval = 1;//这个值一定要设置，否则可能导致sendto()失败
setsockopt(brdcFd, SOL_SOCKET, SO_BROADCAST | SO_REUSEADDR, &optval, sizeof(int));
struct sockaddr_in theirAddr;
memset(&theirAddr, 0, sizeof(struct sockaddr_in));
theirAddr.sin_family = AF_INET;
theirAddr.sin_addr.s_addr = inet_addr("255.255.255.255");
theirAddr.sin_port = htons(4001);
int sendBytes;
if((sendBytes = sendto(brdcFd, msg, strlen(msg), 0,
(struct sockaddr *)&theirAddr, sizeof(struct sockaddr))) == -1){
printf("sendto fail, errno=%d\n", errno);
return -1;
}
printf("msg=%s, msgLen=%d, sendBytes=%d\n", msg, strlen(msg), sendBytes);
close(brdcFd);
return 0;
}

接收程序：

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<netdb.h>
#include<sys/socket.h>
#include<sys/wait.h>
#include<arpa/inet.h>
int main(){
int sockListen;
if((sockListen = socket(AF_INET, SOCK_DGRAM, 0)) == -1){
printf("socket fail\n");
return -1;
}
int set = 1;
setsockopt(sockListen, SOL_SOCKET, SO_REUSEADDR, &set, sizeof(int));
struct sockaddr_in recvAddr;
memset(&recvAddr, 0, sizeof(struct sockaddr_in));
recvAddr.sin_family = AF_INET;
recvAddr.sin_port = htons(4001);
recvAddr.sin_addr.s_addr = INADDR_ANY;
// 必须绑定，否则无法监听
if(bind(sockListen, (struct sockaddr *)&recvAddr, sizeof(struct sockaddr)) == -1){
printf("bind fail\n");
return -1;
}
int recvbytes;
char recvbuf[128];
int addrLen = sizeof(struct sockaddr_in);
if((recvbytes = recvfrom(sockListen, recvbuf, 128, 0,
(struct sockaddr *)&recvAddr, &addrLen)) != -1){
recvbuf[recvbytes] = '\0';
printf("receive a broadCast messgse:%s\n", recvbuf);
}else{
printf("recvfrom fail\n");
}
close(sockListen);
return 0;
}