Mail Archives: djgpp/1998/03/25/10:27:36
Vik Heyndrickx <Vik DOT Heyndrickx AT rug DOT ac DOT be> wrote:
> Salvador Eduardo Tropea (SET) wrote:
> > But perhaps we must investigate if the __null have some advantage and:
> >
> > 1) Define NULL conditionally (no redefinition)
> > 2) If not defined:
> > a) Test the gcc version, if 2.8.0 define with __null
> > b) if prior define with 0.
>
> Conditional redefinition is dangerous since this way NULL might get two
> values that do not compare equal, even when compiled with the same
> compiler version.
> An unconditional #define is best (i.e. preceded with #undef) as it only
> disadvantages programs which are at fault.
>
> Checking whether gcc's version is 2.8.0, won't help a bit:
> for instance the libc library can have been defined using gcc-2.7.2.1
> and hence NULL would be 0. A program compiled with 2.8.0 would then
> define NULL as __null. Like DJ mentionned, a library function like fopen
> can return NULL (=0) and it must be possible that a program compares it
> with NULL (=__null).
You are talking without testing first. You are wrong, __null and 0 are
equivalent, you CAN mix code using __null with code using 0.
In fact the whole RHIDE and my whole editor works 100% fine using the
conditional definition of NULL, that means: MY code uses __null (compiled with
gcc 2.8.0) and the libc uses 0 (compiled with gcc 2.7.2).
The fact is that __null is a C++ symbol and is equivalent to 0. As I explain in
the other mail I didn't have the time to figure out what's the advantage of
__null.
SET
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