C builtin functions?

[Doug Gwyn]

In article <1224 at ulysses.UUCP> jss at ulysses.UUCP (Jerry Schwarz) writes:
>There may have been a recent change of heart, but the Feb 86 draft
>stated (D.1.2):
>
>        All external identifiers declared in any of the  headers
>        [enumerated in the standard] are reserved, whether or not
>        the associated header is included. ... If the program
>        redefines a reserved external identifier, even with a
>        sematicaly equivalent form, the behavoir is implementation
>        defined.
>
>In other words, the compiler can rely on the standard defined meaning
>of any of these functions, e.g. compiling a call to strcpy with an
>appropriate block move instruction.

But it also says somewhere (I left my copy at home) that one can
#undef the function name and be assured that &function_name works,
i.e. there must be an external function definition even if the
compiler normally takes shortcuts.