[CMake] Question about variables, cache, and scope

[Robert Dailey]

Yes, this works perfectly.

It's a bit disappointing that cache variables are, for all intents and
purposes, read-only in functions. The property approach is a bit more
verbose but it functions! I think 'set' needs a new override specifically
for cases like this. Something similar to "PARENT_SCOPE", but something like
"CACHE_SCOPE", that forces CMake to first check for the existance of a cache
variable with that name, and it would take precedence over any identically
named variable in function scope.

On another note, you'd think this would work too but it doesn't:

set( project_count ${new_count} CACHE INTERNAL FORCE )

Thanks!

---------
Robert Dailey


On Mon, Oct 10, 2011 at 2:01 PM, Glenn Coombs <glenn.coombs at gmail.com>wrote:

> Calling a function pushs a new variable scope.  All variables visible in
> the callers scope are copied into the new scope but changes by default only
> affect the callee scope.  You could try using the PARENT_SCOPE option to the
> set command but I'm not sure that will achieve what you want as it only gets
> you to the next scope whereas you really want a global variable.
>
> You can use properties instead of variables as those are explicitly
> scoped.  So something like this:
>
> set_property(GLOBAL PROPERTY project_count "0")
>
> function( define_project ... )
>    get_property(old_count GLOBAL PROPERTY project_count)
>    math( EXPR new_count "${old_count}+1" )
>    set_property(GLOBAL PROPERTY project_count "${new_count}"
> endfunction()
>
> will probably work.
>
> --
> Glenn
>
>
> On 10 October 2011 17:11, Robert Dailey <rcdailey at gmail.com> wrote:
>
>> I have a function that I define in my top-most CMakeLists.txt file (on
>> Windows using CMake version 2.8.6) called define_project() that calls
>> add_executable, sets up compile defintions, etc etc.
>>
>> For each time define_project() is called *anywhere* in the directory
>> hierarchy, I need to increment a global "project_count" variable to keep
>> track of how many projects were created and print that at the very end of
>> the root CMakeLists.txt file.
>>
>> So far my attempts at this have been unsuccessful. I tried creating a
>> cache variable in the root script:
>>
>> set( project_count 0 CACHE INTERNAL "" )
>>
>> Then inside of my function, I do this:
>>
>> function( define_project ... )
>>    math( EXPR count "${project_count}+1" )
>>    set( project_count ${count} )
>> endfunction()
>>
>> However, 'project_count' is always 0 each time that the function is
>> executed.
>>
>> How can I make this work?
>>
>> ---------
>> Robert Dailey
>>
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