C Language Reference, and identifier lengths

Hey folks, new to the forum, if not the language or compiler ;). I have a couple related questions.

1. Is there any C language reference (other than referring to ANSI standards and gnu and Microsoft compatibility)?

2. Are the limits on significant initial characters in an internal identifier or a macro name, or in an external name, the same as ANSI? Or are they relaxed? Microsoft (Visual Studio) has long supported 247 for internal and internal names. gcc supports all characters as signficant.

Thanks!
Kevin