NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/std/c/753

Internet Message Format | 1996-08-06 | 1.9 KB

Path: teal.csn.net!not-for-mail
From: [e-mail] (Thad Smith)
Newsgroups: comp.std.c
Subject: Re: valueless return statement in non-void function
Date: 16 Apr 1996 21:41:21 -0600
Organization: T3 Systems
Message-ID: </[e-mail]>
References: <[e-mail]>
Reply-To: [e-mail]
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In article <[e-mail]>,
walter briscoe <[e-mail]> wrote:
>I recently had trouble moving some K&R code to ISO C.
>
>Specifically, a function without a return statement was used to return a
>value with an implicit return at the } terminating the function.
>
>Section 6.6.6.4 of ANSI/ISO 9899-1990 contains the Semantic restriction
>> If a return statement without an expression is executed, and the value
>> of the function call is used by the caller, the behavior is undefined.
>
>It goes on to say:
>> Reaching the } that terminates the function is equivalent to executing
>> a return statement without an expression.
>
>I am surprised/irritated that the undefined behavior is in the caller
>rather than the called function.

It must be so for compatibility with K&R, as you note.

>The obvious objection to such a statement is that it conflicts with
>prior art.  I would answer that by making the implicit type of
>declarations void rather than int.  That would allow less unreasonable
>prior art to port without complaint.

I haven't worked with much K&R code, so don't know how valid that is.
I suspect that there is lots of legacy code with an implicit int
return type that actually returns values.  My early impression of C
was that much code was designed to be parsimonious.

The following proposal would be somewhat better: if the return type is
explicitly typed, the return statement must provide a value.
Someone will surely trot out some existing working code that violates
this, however.

In the meantime, use a good lint.

Thad