<stdarg.h> (requires <stdio.h>?)

[Mark H. Colburn]

In article <10447 at bloom-beacon.MIT.EDU> scs at adam.pika.mit.edu (Steve Summit) writes:
>The following fails to compile under Microsoft C version 5.1:
>
>	#include <stdarg.h>
>
>	warning(fmt)
>	char *fmt;
>	{
>	va_list arg_ptr;
>	va_start(arg_ptr, fmt);
>	verror("warning", fmt, arg_ptr, 0);
>	va_end(arg_ptr);
>	}
>

If you are going to be strictly pANS your delclaration for 
warning should be:

	warning(char *fmt, ...)
	{
		...
	}

There is no way to express variable arguments given the old
style declaration syntax (at least not portably).

Also, the pANS says that anything which is going to be called
with variable arguments must have a function prototype in
effect at the time of it being called.  So somewhere before 
calling warning(), you wold need to declare...

Function prototypes are generally a good thing, however, they
are not very portable.  I do something like the following in 
my code:


	/* function prototypes */
	#ifdef __STDC__
	int	warning(char *, ...);
	#endif


	#ifdef __STDC__

	warning(char *fmt, ...)

	#else

	warning(fmt)
	char *fmt;

	#endif
	{
	}

It takes up a lot more space, but it allows the code to adapt
to the environment.  It is not all that hard to read once you
get used to it either...

>because the va_end implementation sets arg_ptr to NULL, which
>is nowhere defined.  This strikes me as a bug.  

Va_end should not cause a problem by setting arg_ptr to NULL.
I assume that you mean va_start()?  This may well be because
there is no prototype in scope and/or that there are no 
elipses in your function declaration.

>section of Microsoft's documentation for the va routines shows
><stdio.h> being #included (which would, of course, take care of
>the problem), but I don't think I should have to.  What sayeth
>the pANS?  I know it guarantees you can #include standard header
>files multiple times (a desirable property), but does it ever say
>you have to #include one before you can #include another?  (This
>would not be desirable.)

No, it should not matter what order you include the header files
anymore.  That is the reason for the ability to include headers
multiple times.  If a header file needs definitions which are
in another header, it should include that header.

However, as mentioned before, if you are calling a routine which
uses variable arguments, a prototype must be in scope.  You must
make sure that you include the prototype for any variable
argument functions you call.  Most of these are in stdio or
stdlib.

-- 
Mark H. Colburn                  "Look into a child's eye;
Minnetech Consulting, Inc.        there's no hate and there's no lie;
mark at jhereg.mn.org                there's no black and there's no white."