Path: utzoo!attcan!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!rutgers!rochester!kodak!ektools!randolph
From: randolph@ektools.UUCP (Gary L. Randolph)
Newsgroups: comp.lang.c
Subject: Re: Lvalues and casts
Message-ID: <1912@ektools.UUCP>
Date: 24 May 89 18:32:37 GMT
References: <847@tub.UUCP> <1989May23.225818.9602@utzoo.uucp>
Sender: randolph@ektools (Gary L. Randolph)
Reply-To: randolph@ektools.UUCP (Gary L. Randolph)
Organization: Eastman Kodak, Dept. 47, Rochester NY
Lines: 38

In article <1989May23.225818.9602@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>In article <847@tub.UUCP> net@tub.UUCP (Oliver Laumann) writes:
>>	(int *)cp = ip;
>>
>>The PCC, however, says "illegal lvalue in assignment".  Is this legal
>>C, i.e. is the result of a cast really an lvalue?
>
>No.  Many compilers have accepted it, historically, but it has never
>been legal C and it is not legal ANSI C.

It is my understanding that all of the answers (similar to this one)
are correct, but I have an extension to the original question.  I have
used casts on the LHS of assignment, but without actually assigning to 
the cast.  Example:

func(data, semaphore)
char* data;
char semaphore;
{
if (semaphore=='a')
    *(int *)data = 22;
else if (semaphore=='b')
    *(float *)data = 64;
    .
    .
    .
}

Now the user of func() has supplied a pointer to some type, not 
necessarily a char. semaphore is used to determine the type of 
pointer func() actually received.  The location pointed to by
data is then modified as it is a legal lvalue.  I believe this to
be a typical use of the abused generic pointer, char*.  I would,
of course, use void* if I were using a dpANSI compiler.  It is my
understanding that using casts on the LHS of assignment in this
way is fully portable.  Right???

                         Gary