Why do we need to define _GNU_SOURCE macro before using POLLRDHUP event flag in poll() function?

c sockets opensuse
Don't You Worry Child picture Don't You Worry Child · Aug 13, 2013 · Viewed 7k times · Source

I am using poll() function in my program, I read this link that to use POLLRDHUP flag you have to define _GNU_SOURCE before all header file inclusion. I needed this flag so that polling the socket can tell me whether the client has hung up or not, so that I can terminate the corresponding thread.

By the way I am writing a C program for an 'echo' server which can handle multiple clients concurrently, and I am using GCC 4.1.2 on OpenSuse Linux Enterprise Server 10.3 (x86_64).

Answer

user4815162342 picture user4815162342 · Aug 13, 2013

POLLRDHUP is a non-standard extension (it is missing from POSIX). To prevent polluting the namespace, non-standard extensions are not visible unless you explicitly request them by defining _GNU_SOURCE.

More details on _GNU_SOURCE can be found in previous StackOverflow answers such as this one.

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