ANSI C prototypes

[Stephen Clamage]

ptf at cs.bham.ac.uk (Paul Flinders <FlindersPT>) writes:

>given the file foo.c which contains code for a module within a program, 
>foo.h which defines prototypes for routines in foo.c and bar.c which
>includes foo.h I tend to include foo.h in foo.c so that the compiler
>will tell me if I have been foolish enough to change a routines
>parameters without changing foo.c (the code in foo.c is not yet cast
>in stone so changes are a posibility). This works fine _except_ for
>varargs functions eg.

>in foo.h:
>	extern void ddprintf(const char *fmt, ...);

>BUT in foo.c:

>	void ddprintf(va_alist)
>	va_dcl;

>this causes problems.

As well it should.  What you show is not ANSI C, despite the Subject line
of your posting.  It is the BSD C approach to variadic functions, which is
not quite the same as the ANSI approach.  In ANSI C,
	void ddprintf(const char *fmt, ...);
and
	void ddprintf(va_alist);
are not at all the same.  It sounds like you are using <varargs.h> with
an ANSI compiler, instead of using <stdarg.h>.

If you use the ANSI C <stdarg.h> header, the function delcaration in foo.h
and the function defintion in foo.c become identical.  But you need to
decide if the function is to take a variable *list* of arguments, or *one*
argument of type va_list.  The two notions are not the same.  Refer to the
discussions of <stdarg.h>, printf() and vprint() in any good ANSI C text,
or in the Standard, for more details.
-- 

Steve Clamage, TauMetric Corp, steve at taumet.com