Is there something like the official C documentation? [closed]
You can obtain a PDF copy of the C99 standard (ISO/IEC 9899:1999) from ANSI (and other fine standards organizations) for your private use for a modest fee - I believe it was 18 USD when I bought mine. Having that available is invaluable to me. But if you find a copy in public, then it is contraband.
You can find final committee drafts and current working documents of the C (C0x) Standard Committee at the JTC1, SC22, WG14 web site at the Open Standards Organization. (That's Joint Technical Committee 1, Sub-Committee 22, Working Group 14, I believe).
There is also a hardback book 'The C Standard: Incorporating Technical Corrigendum 1' (also including the Rationale) available for a slightly less modest 85 USD or thereabouts.
One of the best books about C is 'C: A Reference Manual' in its fifth edition. However, you asked for 'ultimate official source of standard C knowledge', and the only 'official' such source is the C standard, plus its corrigenda.
See also the material at http://www.coding-guidelines.com/ and http://c0x.coding-guidelines.com/.
The official C99 standard is available for purchase from your national standards body; however, in practice everyone reads the draft with post-1999 corrections/amendments included, which you can download for free:
There is this online website devdocs
They have multiple API documentations which are well organized. It is free and open-source.
For c doc click this link http://devdocs.io/c/