I am writing a UDP respond server. It works well, when i want to declare a new variable in the main function. No matter what type of the variable is, the sendto() method will arise an error "Address Family not supported by protocol". It is a running error.

What's wired is that i haven't used that variable. I thought it might be an error from stack or somewhere, so i restart the Linux. However, it still exists. And if i delete that line of declaration, the error goes. It really confused me.

Could anybody offer some help or advice? Thanks
My Linux: Ubuntu 8.10 Desktop, kernel 2.6.27

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Can you produce a minimal example which displays this behaviour?

Hey guys, i've fixed it up. The error is raised by the recvfrom() function. The last parameter len must be assigned a number before using it. I thought it could be assigned when the server receives the messages, which proves to be wrong.