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From: gary@darth.UUCP
Newsgroups: comp.lang.c
Subject: Re: Problem with Microsoft C V4.0
Message-ID: <191@darth.UUCP>
Date: Tue, 24-Mar-87 22:03:40 EST
Article-I.D.: darth.191
Posted: Tue Mar 24 22:03:40 1987
Date-Received: Sat, 28-Mar-87 05:30:56 EST
References: <5397@brl-adm.ARPA>
Reply-To: gary@darth.UUCP (Gary Wisniewski)
Organization: Darth Software, Allison Park, Pa. 15101
Lines: 59
Summary: Pros and cons of function prototypes

In article <5397@brl-adm.ARPA> Schauble@mit-multics.arpa (Paul Schauble) writes:
>I've recently acquired Microsoft C version 4.0, replacing Lattice
>version 2.15.  In most aspects, it's a considerable improvement, and I
>wouldn't give up Codeview for anything else I've seen.  However, I just
>had something happen that has badly soured me on the compiler.  The
>problem is this
>
>Within one file I have the function declaration
>
>    void bgunlink_transaction_record (bgfile, client, transaction)
>    BGFILE *bgfile;
>    struct tclient_rec *client;
>    struct ttransaction_rec *transaction;
>    {
>    ....
>    }
>
>The type BGFILE and the structures are correctly declared prior to this.
>Later in the file I have the statement
>
>          bgunlink_transaction_record (&bgfile, &client_rec, rec, &transaction);
>
>Note that they don't match in number or types of arguments.  When
>compiling with /W3 for maximum checking, the compiler SAYS NOT A WORD
>ABOUT THIS.
>[...]

It is not always desirable to have the compiler assume that a previously
declared function is prototyped.  For example:

	void wishy_washy_func(code, optional_arg);

If the second argument in this function is optional (that is, present for
some values of "code" and absent for others), the following are perfectly
acceptable:

	wishy_washy_func(OPTION_A);
	wishy_washy_func(OPTION_B, i);

So long as there is logical consistency, no problems occur.  Of course,
this is a contrived example, and there is no way for the compiler to
typecheck uses.  I don't particularly advocate such constructions, but
wonder whether such considerations were in mind when Microsoft implemented
their compiler.

With Lattice, the above is still possible if a prototype such as:

	wishy_washy_func(enum ww_option, ...);

is defined.  This is probably better, since optional arguments are rarer
and often compromise portability.

I would be curious if anyone else can post a case where default prototyping
is undesirable.

Gary J. Wisniewski
uucp: {allegra, bellcore, cadre}!pitt!darth!gary

"Searching for truth is more rewarding than finding it."