Re: Legacy applications and headers

[Markus Hitter]

Am 19.03.2004 um 16:40 schrieb David Ayers:

> Marcus Müller wrote:
>
> > I found out that GDL2 often uses constructs like the following in its 
> > headers:
> > #ifndef NeXT_Foundation_LIBRARY
> > #include <Foundation/NSArray.h>
...

To verify, I just created an empty "Foundation Tool" in Xcode (Mac OS X 
10.3.3) and NeXT_Foundation_LIBRARY indeed appears to be undefined, 
right after the #import of Foundation/Foundation.h. Tried the same in 
ProjectBuilder on OS X 10.1.5 and it isn't defined either.

To investigate further, I added an #import <Foundation/NSArray.h> and 
#include <Foundation/NSArray.h> to both. Still, everything works fine. 
No errors no warnings ...

> > (For completeness' sake, in the example above, without the manual 
> > definition of NeXT_Foundation_LIBRARY the build will fail on MacOSX 
> > due to redefinitions of NSArray and the like.)

... so I'm not sure how this happens. You always should be able to 
include/import a header as often as you like.

Might be some trouble with the precompiled header mechanism. See Scott 
Tookers posting on  Oct 27 2003 on Apple's Xcode Users list:

> It sounds like the problem you are running into is that we are not 
> detecting when we need to rebuild the precomp header (which we have 
> made improvements on for the next release).
 - this might apply here or not, I don't know. -


> I believe the test was intended to insure ... that we only wanted to 
> use the precompiled headers for Apple's Foundation

It's quite possible this didn't work all the time ...

> Maybe there is another marker we could use?

since you get 95 % of the compilation speed increase by using the 
precompiled header at all we could drop the entire test. Some redundant 
#include's don't matter[1].

If you want to keep the test, since even non-Apple gcc will use 
precompiled headers soon, there should be some platform independent 
test.


Cheers,
Markus




[1] The reason is simple: Usually, headers begin with something like:

#ifndef __FOUNDATION_NSARRAY_H__
#define __FOUNDATION_NSARRAY_H__
...

Since this flag is defined in the precompiled header already, the 
entire file contents is dropped. Left is the exercise to scan the file 
for the corresponding #endif.

See my posting on Jan 1 2003 on GNUstep Discuss for verification.