[Resolved]Broadcast problem in embedded system

[Ivan1120]

Hi guys:
I wrote a program that will send boradcast packet through QUdpsocket. I transfer this program to my board(Beagleboneblack) and run it. I found if I used this code like following:
@cQUdpSocket->writeDatagram(info,info.length,QHostAddress::Broadcast,30000)@

i would get the error message "Unable to send a message"
If i use this code like following, everything is OK.
@cQUdpSocket->writeDatagram(info,info.length,QHostAddress(169.254.255.255),30000)@

Does anyone know why???

P.S. If i run the same program on the linux PC, above two cases are all could work.

[Ivan1120]

Hi guys:
I add a code and everything is ok. Hope this can help other people. But i still don't know why this can work.
@system("ip route add 255.255.255.255 dev eth0");@