how to get source files for nios gnupro tools kit

Ok, thanks so much! the version is 3.1,but I want the new version gnu tool set.

By the way, Can I run linux operating system on nios I system? I have many questions about nios system.

Now, I don't have operating system and so I can not use fopen(). If I port a operating system on nios which support filesystem, what should I add to the compiler I am using such that the compiler is able to use fopen() function?