1. Passing NULL to a c function
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Hi All.
I have a problem with the following wrapper function for Morfit for EU
global function Morfit_engine_load_world( sequence world_file_name, =
sequence world_directory_path, sequence bitmaps_directory_path, atom =
world_mode)
-- int Morfit_engine_load_world(char *world_file_name, char =
*world_directory_path, char *bitmaps_directory_path, =20
-- int =
world_mode)
return =
allocate_string(world_directory_path),
allocate_string(bitmaps_directory_path),
world_mode})
end function
The above function can be called something like this (and works fine) :-
funcval =3D =
SER_DEFINED_BEHAVIOR)
The problem I have is that I need to call it like this :-
Morfit_engine_load_world(NULL,NULL,NULL, EDITOR_MODE); <-- the way you =
could call it in C=20
My question is how can I pass the "NULL" pointers using the wrapper. Am =
I going to have to do a test and have a function call with the =
allocate_string stuff and then another function call for the NULL's?? =
(perhaps test the sequences for an empty sequence or something?). Or is =
there a "NULL" character I can pass.....??=20
This is beyond my C knowledge. Any ideas would be greatly appreciated.
Mark Brown
mabrown at senet.com.au
=20
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<DIV><FONT size=3D2>Hi All.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>I have a problem with the following wrapper function =
for=20
Morfit for EU</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>global function Morfit_engine_load_world( sequence=20
world_file_name, sequence world_directory_path, sequence =
bitmaps_directory_path,=20
atom world_mode)<BR> -- int =
Morfit_engine_load_world(char=20
*world_file_name, char *world_directory_path, char=20
*bitmaps_directory_path, </FONT></DIV>
<DIV><FONT size=3D2> =20
bsp; =20
int world_mode)<BR> return=20
bsp; =20
=20
world_mode})<BR>end function</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>The above function can be called something like this =
(and=20
works fine) :-</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2> funcval =3D=20
SER_DEFINED_BEHAVIOR)</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>The problem I have is that I need to call it like =
this=20
:-</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>Morfit_engine_load_world(NULL,NULL,NULL, =
EDITOR_MODE); =20
<-- the way you could call it in C </FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>My question is how can I pass the "NULL" pointers =
using the=20
wrapper. Am I going to have to do a test and have a function call with =
the=20
allocate_string stuff and then another function call for the NULL's?? =
(perhaps=20
test the sequences for an empty sequence or something?). Or is there a =
"NULL"=20
character I can pass.....?? </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>This is beyond my C knowledge. Any ideas would be =
greatly=20
appreciated.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>Mark Brown</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2><A=20
>
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2. Re: Passing NULL to a c function
- Posted by Mark Brown <mabrown at SENET.COM.AU>
Mar 15, 2000
-
Last edited Mar 16, 2000
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Hi All.
Regarding the NULL pointer problem I've solved it this way.
global function Morfit_engine_load_world( sequence world_file_name, =
sequence world_directory_path, sequence bitmaps_directory_path, atom =
world_mode)
-- int Morfit_engine_load_world(char *world_file_name, char =
*world_directory_path, char *bitmaps_directory_path, int world_mode)
atom world_file_name_ptr,
world_directory_path_ptr,
bitmaps_directory_path_ptr
if length(world_file_name) !=3D 0 then
world_file_name_ptr =3D allocate_string(world_file_name)
else
-- zero length sequence
world_file_name_ptr =3D NULL
end if
if length(world_directory_path) !=3D 0 then
world_directory_path_ptr =3D =
allocate_string(world_directory_path)
else
-- zero length sequence
world_directory_path_ptr =3D NULL
end if
if length(bitmaps_directory_path) !=3D 0 then
bitmaps_directory_path_ptr =3D =
allocate_string(bitmaps_directory_path)
else
-- zero length sequence
bitmaps_directory_path_ptr =3D NULL
end if
return c_func(xMorfit_engine_load_world,{ world_file_name_ptr, =
world_directory_path_ptr, bitmaps_directory_path_ptr, world_mode} )
end function
The above works but if anyone can think of a better/neater way I'd be =
pleased to see it.
Cheers
Mark
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<HTML><HEAD>
<META content=3D"text/html; charset=3Diso-8859-1" =
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<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT size=3D2>Hi All.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>Regarding the NULL pointer problem I've solved it =
this=20
way.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>global function Morfit_engine_load_world( sequence=20
world_file_name, sequence world_directory_path, sequence =
bitmaps_directory_path,=20
atom world_mode)<BR> -- int =
Morfit_engine_load_world(char=20
*world_file_name, char *world_directory_path, char =
*bitmaps_directory_path, int=20
world_mode)<BR> atom=20
world_file_name_ptr,<BR> =
bsp;=20
bitmaps_directory_path_ptr</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2> if length(world_file_name) !=3D 0 =
then<BR> world_file_name_ptr =
=3D=20
else<BR> -- zero length=20
sequence<BR> =
world_file_name_ptr =3D=20
NULL<BR> end if</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2> if length(world_directory_path) =
!=3D 0=20
then<BR> =
world_directory_path_ptr =3D=20
else<BR> -- zero length=20
sequence<BR> =
world_directory_path_ptr=20
=3D NULL<BR> end if</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2> if length(bitmaps_directory_path) =
!=3D 0=20
then<BR> =
bitmaps_directory_path_ptr =3D=20
else<BR> -- zero length=20
bitmaps_directory_path_ptr =3D NULL<BR> end =
if</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2> return =
c_func(xMorfit_engine_load_world,{=20
world_file_name_ptr, world_directory_path_ptr, =
bitmaps_directory_path_ptr,=20
world_mode} )<BR>end function</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>The above works but if anyone can think of a =
better/neater way=20
I'd be pleased to see it.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>Cheers</FONT></DIV>
<DIV> </DIV>
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3. Re: Passing NULL to a c function
- Posted by Mathew Hounsell <mfh03 at UOW.EDU.AU>
Mar 16, 2000
-
Last edited Mar 17, 2000
Hello,
Here is an explanation of : What is NULL?
It is a symbolic constant (atually it's not, but don't worry) to
indicate an impossible pointer.
On most machines, and under most OS'es the first word of a processes
address is part of
reserved memory, therefore a process can never have data there. So address 0 is
an
impossible place to have data.
So C and C++ define an invalid pointer as 0. NULL is just a more
expressive way of
writing it. For example
if( avar != NULL ) {
will make most C/C++ programmers think avar is a pointer. Where as with
if( avar != 0 ) {
avar could be of any type. So I recommend using NULL.
However as NULL is not an official part of C++ Bjarne Stroustop (Spelling?)
recomends you
use 0.
It is defined in the header file <stddef.h>
-------------------------
Sincerely,
Mathew Hounsell
mat.hounsell at excite.com
