[CMake] Setting a value in a sub-project

[Doug Cuthbertson]

Hi Petr,
Thank you so much. I'll try it when I get in to work this morning.

Doug

On Fri, May 20, 2016 at 5:37 AM, Petr Kmoch <petr.kmoch at gmail.com> wrote:

> Hi Doug,
>
> your syntax for `set()` in Foo is incorrect; you're actually setting a
> non-cache variable OPT1 do the value "ON;FORCE".
>
> You want to set the *cache* variable OPT1, which would be done like this:
>
>   set(OPT1 ON CACHE BOOL "Set to OFF|ON (default is OFF) to control build
> of Bar library" FORCE)
>
> Petr
>
> On 20 May 2016 at 11:24, Doug Cuthbertson <doug.cuthbertson at gmail.com>
> wrote:
>
>>
>> CMake (version 3.5.2) surprised me with how it's passing values to
>> sub-projects, so I was wondering if this is expected behavior. Here's an
>> example of what I mean. Let's say I have a project Foo in a directory of
>> the same name. It contains a third-party library called Bar which has a
>> CMakeLists.txt file that looks like:
>>
>>     cmake_minimum_required(VERSION 2.8.12)
>>
>>     option(OPT1
>>       "Set to OFF|ON (default is OFF) to control build of Bar library"
>> OFF)
>>
>>     if(OPT1)
>>       message("Bar: OPT1 is on")
>>     else(OPT1)
>>       message("Bar: OPT1 is off")
>>     endif(OPT1)
>>
>> I then create CMakeLists.txt for Foo that sets OPT1 to ON and includes
>> Bar:
>>
>>     cmake_minimum_required(VERSION 2.8.12)
>>
>>     set(OPT1 ON FORCE)
>>     if(OPT1)
>>       message("Foo: OPT1 is on")
>>     else(OPT1)
>>       message("Foo: OPT1 is off")
>>     endif(OPT1)
>>     add_subdirectory(Bar)
>>
>> The first time I run cmake the message output is:
>>
>>     Foo: OPT1 is on
>>     Bar: OPT1 is off
>>
>> If I run cmake again, I get:
>>
>>     Foo: OPT1 is on
>>     Bar: OPT1 is on
>>
>> If this is expected behavior, is there any way I can ensure Bar receives
>> the value of OPT1 the first time? It makes a huge difference when the
>> option controls, for example, whether a static or dynamic library will be
>> built.
>>
>> Thanks,
>> Doug
>>
>> --
>>
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