C語言socket UDP廣播的收發

要在嵌入式系統里實現廣播收發功能，server.c實現廣播形式指定端口發送廣播信息，client.c綁定指定端口，並阻塞接受廣播內容然后打印，程序非常簡單，不過有一點需要注意，那就是setsockopt()函數的使用。使用不當很可能會出問題。通過SO_REUSEADDR選項可以實現端口號的重用，SO_BROADCAST選項表示要發送的是廣播信息，optval參數要給合理的初始值（這里是1），否則很可能會發送失敗.

發送廣播的程序server.c：

#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;//這個值一定要設置，否則可能導致sendto()失敗
	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;
}

接收廣播的程序client.c：

#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;
	// 必須綁定，否則無法監聽
	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;
}

編譯在linux里編譯調試，window編譯會提示找不到對應頭文件目錄，