[CMake] How to define datafiles?

[Michael Wild]

On 04/26/2011 03:09 PM, Michael Hertling wrote:
> On 04/26/2011 06:20 AM, Michael Wild wrote:
>> On 04/25/2011 05:03 PM, Michael Hertling wrote:
>>> On 04/25/2011 01:53 PM, Michael Wild wrote:
>>>> On 04/25/2011 12:48 PM, Michael Hertling wrote:
>>>>> On 04/24/2011 04:56 PM, Campbell Barton wrote:
>>>>>> 2011/4/23 YangXi <jiandingzhe at msn.com>:
>>>>>>> In my program, I have several pictures and plain-text data
>>>>>>> files. Usually in a unix system, they should be placed on
>>>>>>> /usr/share/my_program/some_place. How could I define those
>>>>>>> files in CMakeLists, and make their location known by the
>>>>>>> program? Thanks!
>>>>>>
>>>>>> first define the prefix in CMake so you can use it in your C
>>>>>> program. add_definitions(-DPREFIX="${CMAKE_INSTALL_PREFIX}")
>>>>>>
>>>>>> the C program can then add the rest of the path
>>>>>> "share/my_program/some_place"
>>>>>>
>>>>>> You'll also want to install this file so its copied on "make
>>>>>> install"
>>>>>
>>>>> Alternatively, you might use configurable headers or even
>>>>> configurable sources and have CMake write the afore-noted paths
>>>>> to them when your project is configured. Suppose you have a
>>>>> config.h.in template in CMAKE_CURRENT_SOURCE_DIR with the line:
>>>>>
>>>>> #define DATDIR @DATDIR@
>>>>>
>>>>> Now, your CMakeLists.txt might contain
>>>>>
>>>>> SET(DATDIR "${CMAKE_INSTALL_PREFIX}/share/..." CACHE PATH "...") 
>>>>> CONFIGURE_FILE(config.h.in config.h @ONLY) 
>>>>> SET_SOURCE_FILES_PROPERTIES(${CMAKE_CURRENT_BINARY_DIR}/config.h 
>>>>> PROPERTIES GENERATED TRUE)
>>>>>
>>>>> to turn the ${CMAKE_CURRENT_SOURCE_DIR}/config.h.in template into
>>>>> the ${CMAKE_CURRENT_BINARY_DIR}/config.h header with the DATDIR
>>>>> definition set to "${CMAKE_INSTALL_PREFIX}/share/..." or whatever
>>>>> you've possibly assigned to DATDIR on CMake's command line or
>>>>> GUI. E.g., an invocation as "cmake -DDATDIR=/var/lib ..." would
>>>>> result in DATDIR being set to /var/lib regardless of the
>>>>> CMAKE_INSTALL_PREFIX variable's value.
>>>>>
>>>>> However, with both methods, your project's binaries will
>>>>> incorporate DATDIR or PREFIX as hard coded paths, so they might
>>>>> not run before the entire package is installed; in particular,
>>>>> they might fail to run from the build tree, e.g. for testing
>>>>> purposes. For this reason, you should consider to provide an
>>>>> additional way for the binaries to learn of the data directory,
>>>>> e.g. by examining an environment variable DATDIR, and use the
>>>>> hard coded paths just as a fallback.
>>>>>
>>>>> Regards,
>>>>>
>>>>> Michael
>>>>
>>>> Or alternatively, hard-code the _relative_ path from the binary to
>>>> the data directory and make sure in the build-tree and the
>>>> install-tree you use the same relative path. Of course, then you
>>>> would need a reliable way of figuring out the applications absolute
>>>> path at runtime, which can be quite tricky on some platforms. Often
>>>> it is a convention that argv[0] contains the applications full
>>>> path, but that is only a convention and the calling program could
>>>> set it to anything. On Linux systems interrogating /proc/* is more
>>>> reliable, other *Nix systems have similar facilities, Mac OS X and
>>>> Windows have dedicated functions. See [1] for a rather
>>>> comprehensive overview. If you are using Qt anyways, you can use 
>>>> QCoreApplication::applicationDirPath() or 
>>>> QCoreApplication::applicationFilePath() [2] to do obtain this 
>>>> information a rather portable way.
>>>>
>>>> HTH
>>>>
>>>> Michael
>>>>
>>>> [1] 
>>>> http://stackoverflow.com/questions/1023306/finding-current-executables-path-without-proc-self-exe/1024937#1024937
>>>>
>>>>
>>>>
>> [2] http://doc.trolltech.com/4.7/qcoreapplication.html#applicationDirPath
>>>
>>> Indeed, a quite interesting approach, but does it work on Windows if
>>> an executable's installation directory resides on a different drive
>>> than its data directory, or in other words: Is there a relative path
>>> which leads from C: to D:, e.g.? At the first try, I haven't been
>>> successful.
>>>
>>> Regards,
>>>
>>> Michael
>>
>> No, that wouldn't work, unless you mount the other partition using
>> volume mount points. But usually the binary and data files are much
>> closer together and share a common directory in %ProgramW6432% or
>> %ProgramFiles(x86)%.
>>
>> Michael
> 
> Yes, that's true, indeed. OTOH, I wouldn't like to inhibit such a
> configuration a priori, and people have the weirdest set-ups and
> requirements. In the end, the incorporation of hard coded paths -
> relative or absolute - is particularly critical w.r.t. a compiled
> package's relocation capability.
> 
> Regards,
> 
> Michael

Either you make it configurable in your CMakeLists.txt, and/or (and IMHO
one should always do this) make the data and configuration paths
configurable via environment variables, and also possibly with command
line switches.

Michael