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POUDP Socket broadcast and ifaddrstruct
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10179583
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0
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2
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0
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2012-04-16T18:31:03.717
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2012-04-16T19:07:55.550
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1336989
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1
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318
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I have a problem with the client side of an application I have to develop. The first phase I have to implement is a "scan" of the network, searching for other users. I decided to use UDP sockets, and they work properly. If I use the broadcast ip address (getnamebyhost("192.168.1.255")) it works fine. The problem is that the application have to work on different networks, and I don't know the ip address (192.168 or 10.0 or else). I have to learn the address, so I found on the net to use getifaddr(). Here's the code: <pre><code>#include <stdio.h> #include <sys/types.h> #include <ifaddrs.h> #include <netinet/in.h> #include <string.h> #include <arpa/inet.h> #include <string.h> int FindMyIp(); int IsConnected(); char *myIpAddr, *myMask, *myBroad; int main (int argc, const char * argv[]) { int checkConnection=0; checkConnection = IsConnected(); while (checkConnection == 0) { printf("Checking again..\n"); checkConnection = IsConnected(); sleep(2); } checkConnection=0; printf("\nConnected to a new network..\n"); while (checkConnection == 0) { checkConnection = FindMyIp(); if (checkConnection==0) { sleep(2); } } printf("My IP is %s\n", myIpAddr); printf("My Mask is %s\n", myMask); printf("The Broadcast IP is %s\n", myBroad); return 0; } int IsConnected() { if (system("ping -c 1 www.google.com")){ return 0; } else { return 1; } } int FindMyIp() { struct ifaddrs * ifAddrStruct=NULL; struct ifaddrs * ifa=NULL; void * tmpAddrPtr=NULL; printf("Acquiring interface information.. "); getifaddrs(&ifAddrStruct); printf("Checking for wanted interface..\n"); int i=0, connected=0; ifa = ifAddrStruct; while (i!=1) { if ((ifa ->ifa_addr->sa_family==AF_INET)&&(ifa->ifa_name[0]=='e')&&(ifa->ifa_name[1]=='n')&&(ifa->ifa_name[2]=='1')) { i=1; connected=1; } else { if (ifa->ifa_next == NULL) { printf("error"); return connected; } ifa = ifa->ifa_next; } } char addressBuffer1[INET_ADDRSTRLEN]; char addressBuffer2[INET_ADDRSTRLEN]; char addressBuffer3[INET_ADDRSTRLEN]; tmpAddrPtr=&((struct sockaddr_in *)ifa->ifa_addr)->sin_addr; inet_ntop(AF_INET, tmpAddrPtr, addressBuffer1, INET_ADDRSTRLEN); myIpAddr = addressBuffer1; tmpAddrPtr=&((struct sockaddr_in *)ifa->ifa_netmask)->sin_addr; inet_ntop(AF_INET, tmpAddrPtr, addressBuffer2, INET_ADDRSTRLEN); myMask = addressBuffer2; tmpAddrPtr=&((struct sockaddr_in *)ifa->ifa_broadaddr)->sin_addr; inet_ntop(AF_INET, tmpAddrPtr, addressBuffer3, INET_ADDRSTRLEN); myBroad = addressBuffer3; return connected; } </code></pre> So in myBroad I should have saved the broadcast ip address, and it's, I can print it with printf, but when I pass it to the socket by: struct hostent *hptr = gethostbyname(myBroad); it won't work! Where's the error? Thanks
Tags
<c><sockets><udp><gethostbyname>
Title
UDP Socket broadcast and ifaddrstruct
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1. USphcaze
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