Any full-blown framework for C?

I'm starting to learn the C language, and I'm used to having a lot of classes at my disp开发者_如何学Pythonosal in the .NET Framework. Is there any sort of framework like that for C? I'd prefer if it were cross-platform. Thanks.

How about X11? It's a windowing system and the set of API combined. It's huge, by the way. And it's cross-platform.

Or, how about GTK+? It's a C-based GUI library, again cross-platform. And it's huge.

For non-GUI things, how about POSIX? It's a set of common C functions, usable across wide range of operating systems (i.e. basically all.).

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