Subj : Re: Old C-program
To   : borland.public.cpp.borlandcpp
From : Vladimir Grigoriev
Date : Tue Oct 11 2005 05:08 pm

Also it is interesting to note that in the same source module I found the
following code
if ((bentry = (BENTRY *)GetEntryBlock() ) != NULL)
Why does a programmer in one case use (char *) pointer and in another case
use (BENTRY *) pointer when compares with NULL? It is strange...

Vladimir Grigoriev

"Vladimir Grigoriev" <vlad.moscow@mail.ru> wrote in message
news:434ba00f$1@newsgroups.borland.com...
> Thank Ed
> But another question arises.
> If  benrty is equal to NULL why below the checking the following statement
> is present
> bentry->key = key ?
> It is executed for any bentry (NULL or not NULL).
> Maybe it is simply a bug?
>
> Vladimir Grigoriev
>
>
> "Ed Mulroy" <dont_email_me@bitbuc.ket> wrote in message
> news:434b9d74$1@newsgroups.borland.com...
> > Before the 1986 provisional C standard many compilers used C as taught
in
> > version 1 of the K&R book.  It used this for NULL,
> >     #define NULL ((char *)0)
> >
> > The pre-1986 compilers normally did little type checking.  Later
compilers
> > are more strict.
> >
> > The cast in this line:
> >     if ((char *) bentry == NULL )
> > is used to allow comparing the pointer to NULL when the pointer is not a
> > char* type but NULL is a char* type.
> >
> > Compilers which conform to ANSI C, C as used since 1986 use
> >     #define NULL 0
> > and with them it is valid for any pointer type to be compared to zero.
> >
> > .  Ed
> >
> > > Vladimir Grigoriev wrote in message
> > > news:434b8037@newsgroups.borland.com...
> > >
> > > I get an old-style C program and cannot understand some code.
> > > Here it is.
> > >
> > > typedef struct BlockEntry
> > > {
> > >      struct BlockEntry * next;
> > >      char  name[4];
> > >      unsigned long key;
> > >      int lock;
> > > } BEntry;
> > >
> > >
> > > int SomeFunction( bentry )
> > > BEntry * bentry;
> > > {
> > >        unsigned long key;
> > >
> > >        if ((char *) bentry == NULL )
> > >           key = ONE_CONSTANT;
> > >        else
> > >           key = ANOTHER_CONSTANT;
> > >
> > > /* some code that I have skipped */
> > >
> > >       bentry->key = key;
> > >
> > >       return 0;
> > > }
> > >
> > > I cannot understand the following code
> > > if ((char *) bentry == NULL )
> > > What did a programmer want to say?
> > > Is the value of (char *)bentry is different form the value of bentry?
> >
> >
>
>

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