C Builtin Functions

[Jerry Schwarz]

> I'm surprised that with all this discussion on built-ins, nobody has pointed
> out how the C standard specifies that it should work.  My copy of the standard
> is pretty old and has been stolen, so perhaps it was removed in a later
> specification?
> 

It was about the 3rd item posted in the discussion.  But here it is
again (Februray 1986 draft)

        D.1.2 Headers

        ... All external identifiers declared in any of the headers
        [i.e. as specified in the standard] are reserved, whether or
        not the associated header is included. All external
        identifiers and macro names that begin with an underscore are
        also reserved.  If the program redefines a reserved external
        identifier, even with a semantically equivalent form the
        behavior is implementation defined. ...

        D.1.3 Use of library functions

        ... Any function declared in a header may be implemented as a
        macro defined in the header, so a library function should not
        be declared explicitly if its header is included. ... The use
        of #undef to remove any macro definition will also ensure
        that  an actual function is referenced.

To me this seems perfectly reasonable.  Note in particular that a
vendor is required to tell you what will happen if you try to redefine
one of the reserved identifiers.  

Jerry Schwarz 
Bell Labs, MH  
ulysses!jss