Re: Conditional dependencies

Is this a good time to mention that GCC 3.4 can do precompiled headers?  
You simply compile the .h files in to header.h.gch and then  the 
compiler reads those, if they exist.

I haven't put together any a-a-p code to build them yet,  it seems like 
an additional path for the dependencies.

Ian

Bram Moolenaar wrote:

>Lars Ivar Igesund wrote:
>
>  
>
>>It struck me once that the dependencies found by ddepcheck wasn't 
>>necessarily correct at all times. This is due to the possibility to 
>>conditionally include/exclude parts of the source code using compiler 
>>switches. Correct dependencies for any given compilation run would 
>>therefore need ddepcheck to also look at these switches. I have 
>>implemented this (looks hairy at the moment) on my local copy of 
>>ddepcheck, but there is another problem that might, well, be a problem.
>>
>>If the switches are changed, changing the dependencies, but not the 
>>source code itself, can this be handled by A-A-P? I suppose dependency 
>>checking of C/C++ where includes are conditionally included/excluded by 
>>define might have the same problem.
>>    
>>
>
>There are two ways to do the dependency checking:
>1. Without looking at conditionals.  Thus more files are found than what
>   is actually used.
>2. Taking conditionals into account.  Then the list of files is
>   accurate, but may change when the circumstances change.
>
>In the first case there are no tricks, no need to check the dependencies
>again when you change conditionals.
>
>In the second case, the build signature should include the
>circumstances.  For C these are the preprocessor symbols.  This should
>already happen, since Aap uses a signature for the build commands.
>
>When an included file changes that may define different symbols, it's
>more complicated.  Example:
>
>	file.c:
>		#include "defines.h"
>		#include "includes.h"
>	
>	defines.h:
>		#define ONE
>		// #define TWO
>	
>	includes.h:
>		#ifdef ONE
>		# include "one.h"
>		#endif
>		#ifdef TWO
>		# include "two.h"
>		#endif
>
>Depending on whether ONE and/or TWO are defined in defines.h, the
>dependency of includes.h changes.  But you can't see that when just
>looking at includes.h.
>
>As it is when using gcc it will work correctly.  It just verified that.
>You always edit a file that's already one of the dependencies, thus Aap
>will run the dependency checker.
>
>Perhaps there are situations where a change isn't noticed?
>
>  
>


-- 


*Ian S. Nelson
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