The book was useful, if you ignored Schildt's annotations, and just used it to get the text of the standard (or most of it).
Review of the above book by Clive Feather:
https://www.lysator.liu.se/c/schildt.html
Of Schildt's C: The Complete Reference, by Peter Seebach:
https://www.seebs.net/c/c_tcn4e.html