[CMake] How to define datafiles?

[Michael Hertling]

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