[CMake] Best way to handle application data path for local run vs. installation

[Bill Somerville]

On 30/11/2015 02:10, Dmitry Marakasov wrote:
> Hi!
>
> This question bugs me for a long time so I though maybe someone has
> a solution. I have a project which includes an application and some
> data for it. An application needs to know path to its data files, so
> I pass it via compiler definition: ADD_DEFINITIONS(-DDATADIR="...")
>
> The problem is that this path is different based on whether I want to
> run the application from build directory:
>
> ADD_DEFINITIONS(-DDATADIR="${PROJECT_SOURCE_DIR}/data")
>
> or want to install it systemwide:
>
> ADD_DEFINITIONS(-DDATADIR="${CMAKE_INSTALL_PREFIX}/share/myapp")
>
> I want my project to both run from build directory and to be
> installable systemwide, without the need to rebuild or specify extra
> options.
>
> - I don't want to make an applications search for its data relative
>    to executable path
>    - There's no cross-platform way to get an executable path
>    - This will break when executable is moved or hardlinked
> - I don't want to try both paths, as this is error prone, as installed
>    executable may pick data files from repository or vice versa
> - I don't want to make user specify additional cmake flags like
>    -DSYSTEMWIDE_INSTALLATION or -DRUN_LOCALLY.
> - I don't want to use any wrapper scripts
> - I don't want to build two executables
>
> The best solution would be for cmake to fix path in executable file
> right after installation, something similar to what cmake does with
> rpaths. Or there could be a cross-platform way for executable to know
> whether it was installed which I've missed.
>
> Any ideas?
>
How about reading the path from a configuration file. The default when 
there is no configuration file can be a relative path in the build tree. 
Use an 'install(CODE ...)' command to write a configuration file to be 
shipped with the executable that contains the path to use when 
installed. Application reads configuration file if it is there and uses 
contents to determine the path to the data.

Regards
Bill.