[clarry]

Well, OP asked for source of truth. Nothing comes as close as the standard itself.

Honestly, I think any programmer writing C today should have it around for reference. And yeah you kinda need to read it too, or you won't be able to refer much.

That said, no need to read it cover to cover. There's stuff one can earmark as being there but ignore until it's actually needed (for example: the grammar and all the library functions).

And speaking of tedu, I would recommend to the OP that they get in the habit of checking out the OpenBSD man pages for libc functions.

[kevindong]

> Well, OP asked for source of truth. Nothing comes as close as the standard itself.

An unfortunate reality is that standards are not always strictly followed (whether intentionally or not). C is almost certainly better about following the standards than other pieces of tech (notably web browsers), but I doubt the C compilers are perfectly compliant if you look hard enough.

[sramsay]

I actually have very few $200 PDFs lying around.

Do you really go purchase the standard documents from ISO? Or does your employer? I'd love to have the actual standard "around for reference," but 700-page technical documents from ISO are not cheap.

[clarry]

The next best thing is the latest draft standards, which are available online for free (and I always have them on my laptop, PC, and personal server). Differences between them and final official standard are not important. Search for N1256, N1570. Or grab them here. http://www.open-std.org/jtc1/sc22/wg14/www/standards

(There are more readable html versions floating about)