From: Hans-Bernhard Broeker <broeker AT acp3bf DOT physik DOT rwth-aachen DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: use NULL in c++
Date: 29 Feb 2000 17:48:19 GMT
Organization: Aachen University of Technology (RWTH)
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To: djgpp AT delorie DOT com
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Florian X <dos DOT fire AT aon DOT at> wrote:

> If I use NULL in c++, the compiler prints me this error:

You forgot to show us *how* you use NULL, in your program. That's an
important detail you're hiding from us.

> dc.cc:167: ANSI C++ forbids implicit conversion from `void *' in argument
> passing

The error message says it all, I think. Unlike C, C++ does not allow
to use a 'void *' expression (like NULL) where a pointer to some
specific type is requested. In C, you can do that, as the 'void *'
will automatically be casted to the right type. That's the 'implicit
conversion' the error message speaks of. In C++, you have to write
down the cast, in the source code. The typical example:

	some_type *p = malloc(number*sizeof(some_type));

does not work in C++, although it is perfectly valid C. In C++, you
have to write the following, instead:

	some_type *p = (some_type*) malloc(number*sizeof(some_type));

(Or use one of the specialized cast operators offered by C++, like
'static_cast')
-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.