Windows 7中的UDP广播-是否有效？

Question

I'm trying to write some code under Windows 7 to broadcast across my local network and can't get the following code to work. I come from a Linux background so apologies for style - the full code compiles etc and works and if I use an address of:

unsigned long broadcastAddr = inet_addr("192.168.10.0") | ~(inet_addr("255.255.240.0"));

Then that works fine, I just would really like to use the preferred INADDR_BROADCAST/255.255.255.255 method.

<snip>
SOCKET sockfd;
int broadcast = 1;

WSADATA wsaData;    // Windows socket

// Initialize Winsock
if (WSAStartup(MAKEWORD(2,2), &wsaData) == SOCKET_ERROR) {
    perror("WinSock Error");
    getc(stdin);
    exit(EXIT_FAILURE);
}
if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
    perror("Socket Error");
    getc(stdin);
        exit(1);
}

if ((setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, (char *)&broadcast, sizeof(broadcast))) == SOCKET_ERROR) {
    perror("Setsockopt - SOL_SOCKET");
    getc(stdin);
    exit(1);
}

struct sockaddr_in recvaddr;
recvaddr.sin_family = AF_INET;
recvaddr.sin_port = htons(PORT);
recvaddr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
memset(recvaddr.sin_zero,'\0', sizeof(recvaddr.sin_zero));

int numbytes = 0;
while ((numbytes = sendto(sockfd, greet, strlen(greet) , MSG_DONTROUTE, (struct sockaddr *)&recvaddr, sizeof(struct sockaddr_in))) != -1) {
        printf("Sent a packet %d\n", numbytes);
        Sleep(100);
}

Answer 1

There is a huge bug in Windows 7 for UDP broadcast which makes broadcasting on 255.255.255.255 not work on most windows 7 install: https://serverfault.com/questions/72112/how-to-alter-the-global-broadcast-address-255-255-255-255-behavior-on-windows

Basically it will send the broadcast only on a single network interface, which could be anything, even something like a VM network interface or bluetooth one, which can end up not broadcasting to any device.

Answer 2

Unless my bit maths is out, inet_addr("192.168.10.0") | ~(inet_addr("255.255.240.0")) inet_addr("192.168.10.0") | ~(inet_addr("255.255.240.0")) is the same as inet_addr("192.168.15.255") which is the broadcast address for that subnet.

It looks to me like the most likely possibility is not that the sending code is wrong but that the receiving code is wrong. What address have you bound the receiving socket to? What subnet is it on?