[CMake] What is the correct way to manage a possibly user-defined directory?

[Cedric Doucet]

Hi Petr! 

Thank you very much! 
Now, I understand when an option should be used! :) 

I tried 
set(FOO_DIR "" CACHE PATH "Provide path to FOO library here") 
and it works fine with the user interface! 

Cheers, 

Cédric 

----- Mail original -----

> De: "Petr Kmoch" <petr.kmoch at gmail.com>
> À: "Cedric Doucet" <cedric.doucet at inria.fr>
> Cc: cmake at cmake.org
> Envoyé: Lundi 18 Mai 2015 12:04:21
> Objet: Re: [CMake] What is the correct way to manage a possibly user-defined
> directory?

> Hi Cedric.

> if(EXISTS) does not automatically dereference its argument. So your current
> code is testing for the existence of a directory literally named "FOO_DIR".
> You want to dereference the variable:

> if(NOT EXISTS ${FOO_DIR})

> Second, option() is intended for on/off options only (a checkbox). If you
> want to provide a path selector, use set(... CACHE) instead:

> set(FOO_DIR "" CACHE PATH "Provide path to FOO library here")

> This will create a path selector widget in CMake UI, with "Provide path to
> FOO library here" serving as its tooltip/documentation.

> Petr

> On Mon, May 18, 2015 at 11:48 AM, Cedric Doucet < cedric.doucet at inria.fr >
> wrote:

> > Hello,
> 

> > I would like to let users choose between providing third party libraries or
> > let CMake download them.
> 
> > To do that, I try to write a simple code like this to manage a third party
> > library FOO of an executable MY_EXEC:
> 
> > =================================================
> 
> > IF(NOT EXISTS FOO_DIR)
> 
> > MESSAGE(STATUS "FOO LIBRARY WILL BE DOWNLOADED AND INSTALLED")
> 
> > # download and install FOO, define FOO_DIR
> 
> > ENDIF()
> 
> > INCLUDE_DIRECTORIES(MY_EXEC ${FOO_DIR}/include)
> 
> > TARGET_LINK_LIBRARIES(MY_EXEC ${FOO_DIR}/include)
> 
> > =================================================
> 
> > To do that, I think the user should have the possibility to define FOO_DIR
> > with an option.
> 
> > So, I put the line
> 
> > OPTION(FOO_DIR)
> 
> > before the code below.
> 

> > However, it doesn't seem to work because FOO_DIR does not seem to be
> > defined.
> 
> > The message "FOO LIBRARY WILL BE DOWNLOADED AND INSTALLED" always appears,
> 
> > - even if I type "cmake -D FOO_DIR=path", where path is a user-defined path
> > to FOO library,
> 
> > - even if I put a default value to FOO_DIR with OPTION(FOO_DIR path), where
> > path is a hard-coded path to FOO.
> 

> > Where does I make a mistake here?
> 
> > What is the correct way to manage FOO_DIR when it can be defined by a user?
> 

> > Note: the next step is to define FOO_DIR in a FindFoo.cmake file and use
> > find_package(Foo), but it's not my goal yet.
> 

> > Thank you very much for your help!
> 

> > Cédric
> 

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