🚀 go-pugleaf

crow@coos.dartmouth.edu (Preston F. Crow) wrote:

> Christopher R Volpe <volpe@ash.crd.ge.com> writes:
> 
> >comp.std.c answer: The compiler is allowed to know the semantics of
> >printf, and should know that the printf function will not modify
> >flag_pt, despite the fact that other user-defined functions could.
> 
> No, the compiler can't assume anything about printf(), as the user
> could have stupidly defined his own function of the same name,
> overriding the expected behaviour of the version in libc.
> 
> In some of my Mach programming, I've done just that.  [Well, with
> different functions, where the normal version had problems, but
> still...]
> 
> Never expect a compiler to be smart, but always be prepared for it to
> outsmart you.

NO.  The compiler may assume that you have not replaced printf() with
another function.  Replacing a standard library function results in
undefined behavior -- the compiler may do anything.  See ISO 7.1.3.

Just because some compiler allowed you to do this, does not mean it is
legal.

Michael M Rubenstein