Re: Use command line defines vs defining in header files.

Re: Use command line defines vs defining in header files.

[rlau]

Now, let get back to the my question.
Anyone please.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Can anyone give me a strong argument as whether defining constants for
conditional compiling as compiler argument vs.
   defining thems in header files?

for examples:



test.h
#ifdef COMPILER_OPT1
:
#else
:
#endif

#ifdef COMPILER_OPT2
:
#else
:
#endif
-------------------------------------------

So, if I would be defining COMPILER_OPT1 as compiler argument, I would do
something like gcc -d COMPILER_OPT1 test.cpp.

If I would defining COMPILER_OPT1 in header files, I would define it in
test.h before #ifdef COMPILER_OPT1.

Re: Use command line defines vs defining in header files.

[Gerald Pfeifer]

On Mon, 28 Aug 2000, Matt Minnis wrote:
> On a similar note, why is #ifdef XXX used more than #if XXX?

If you #define SOMETHING, #ifdef SOMETHING evaluates to true, but
#if SOMETHING causes an error.

Gerald
-- 
Gerald "Jerry" pfeifer@dbai.tuwien.ac.at http://www.dbai.tuwien.ac.at/~pfeifer/

Re: Use command line defines vs defining in header files.

[Michael Meissner]

On Mon, Aug 28, 2000 at 03:31:46PM -0500, Matt Minnis wrote:
> On a similar note, why is #ifdef XXX used more than #if XXX?
> 
> Is there a technical reason or just that's the way it has been done?

The two are not the same thing.

	#if name

tests if name != 0 (with undefined names being 0, though I believe some pre-ISO
C compilers would give an error or a warning if name was not defined), while

	#ifdef name

would be positive even if name was defined as either the empty string, or 0.
In addition, if name is not defined as an integer constant expression (for
example, it contains a call or a structure member reference), the plain #if
would barf on it.

	#if defined(name)

is indeed equivalent to #ifdef name, but it is clunkier.

-- 
Michael Meissner, Red Hat, Inc.
PMB 198, 174 Littleton Road #3, Westford, Massachusetts 01886, USA
Work:	  meissner@redhat.com		phone: +1 978-486-9304
Non-work: meissner@spectacle-pond.org	fax:   +1 978-692-4482

Re: Use command line defines vs defining in header files.

[Matt Minnis]

On a similar note, why is #ifdef XXX used more than #if XXX?

Is there a technical reason or just that's the way it has been done?

Thanks,

Matt Minnis

At 03:23 PM 8/28/2000, Jan Dvorak wrote:
>On Mon, Aug 28, 2000 at 03:11:32PM -0500, rlau@csc.com wrote:
> >
> > Can anyone give me a strong argument as whether defining constants for
> > conditional compiling as compiler argument vs.
> >    defining thems in header files?
> >
> > for examples:
> >
>
>Not all compilers supports -D, and you can get to line length limit on 
>some systems (255 on dos ?). -D is useful when you have to specifi one or 
>more really dependent argumenst (such as -DHAVE_CONFIG_H in autoconf does), and
>you get better readibility of code to search for #define than search 
>through all the (generated) Makefile.
>
>Jan Dvorak <johnydog@go.cz>

Cthulhu for President. Why settle for a lesser evil?

=========================================================
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Re: Use command line defines vs defining in header files.

[Jan Dvorak]

On Mon, Aug 28, 2000 at 03:11:32PM -0500, rlau@csc.com wrote:
> 
> Can anyone give me a strong argument as whether defining constants for
> conditional compiling as compiler argument vs.
>    defining thems in header files?
> 
> for examples:
> 

Not all compilers supports -D, and you can get to line length limit on some systems (255 on dos ?). -D is useful when you have to specifi one or more really dependent argumenst (such as -DHAVE_CONFIG_H in autoconf does), and
you get better readibility of code to search for #define than search through all the (generated) Makefile.

Jan Dvorak <johnydog@go.cz>

Use command line defines vs defining in header files.

[rlau]

Can anyone give me a strong argument as whether defining constants for
conditional compiling as compiler argument vs.
   defining thems in header files?

for examples:



test.h
#ifdef COMPILER_OPT1
:
#else
:
#endif

#ifdef COMPILER_OPT2
:
#else
:
#endif
-------------------------------------------

So, if I would be defining COMPILER_OPT1 as compiler argument, I would do
something like gcc -d COMPILER_OPT1 test.cpp.

If I would defining COMPILER_OPT1 in header files, I would define it in
test.h before #ifdef COMPILER_OPT1.