cppreference.com is by far the best resource for the language and the standard library. It is also well organized and easy to navigate. "errors creep in" is a well-taken complaint about life in general, not cppreference.
I implemented a printf format checker for D, which checks that the argument types are compatible with the format specifiers. (This is really a nice feature, I should have done it long ago.)
To be successful, it had to correctly deal with every nuance of the printf spec. cppreference got a couple of these incorrect wrt to modifiers. Not something a routine user would notice, but a pedantic one would. (Sorry, I don't remember exactly what the mistakes were.)
I still use cppreference because it is so dang convenient. But I don't rely on it when perfection is required.
It's really too bad that copyright forces everyone writing a manual to rewrite & rephrase things. I wish the C++ Standard was online.
One online reference I dearly like is https://www.felixcloutier.com/x86/index.html which has saved me so much time. But it was created by scanning the actual reference manuals, so barring scanning errors, it is exactly correct. I gave up using reformulations of the CPU instruction set long ago, they had too many mistakes.
You might be interested in the EXEgesis project, which is also a machine interpretation of x86 documentation, but which includes several patches for unfixed errata therein.
