Checking whether Network IF can access Internet in C Linux?

I'm writing a simple library for checki开发者_运维知识库ng the internet access status of network interfaces by C on Linux.

• Checking the status for all network interfaces (configured or not configured)

Would you please give me where i can refer ( such as documents, example code ...) or any hints?

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The simplest method is probably to check for the existence of a default route through that interface. You could call out to /bin/ip route to do this.