CMake Config uses absolute paths.

[izonfreak]

Out of the box it is not possible to import cjson using find_package cmake command If you have not build the library yourself. This is due to the CMakeLists.txt file using CMAKE_INSTALL_FULL_* variables from GNUInstallDirs module which according to the documentation should not be used on install() commands.

In any case the fix is simple, just replace CMAKE_INSTALL_FULL_* variables with their relative counterparts (i.e., CMAKE_INSTALL_LIBDIR, CMAKE_INSTALL_BINDIR, etc.)

If you want a little bit more detail. What happens is that if you use the FULL variables in install commands. The cmake config files will use the FULL path as the installation prefix instead of calculating the path at runtime base on the file location. You can see this in the cjson.cmake file (more or less line 48) and in cjson_utils.cmake where when using the FULL variant the code looks like this:

# The installation prefix configured by this project.
set(_IMPORT_PREFIX "/<my-person-install>/cjson/cjson-1.7.19/")

While when using the relative paths it looks like this:

# Compute the installation prefix relative to this file.
get_filename_component(_IMPORT_PREFIX "${CMAKE_CURRENT_LIST_FILE}" PATH)
get_filename_component(_IMPORT_PREFIX "${_IMPORT_PREFIX}" PATH)
get_filename_component(_IMPORT_PREFIX "${_IMPORT_PREFIX}" PATH)
get_filename_component(_IMPORT_PREFIX "${_IMPORT_PREFIX}" PATH)
if(_IMPORT_PREFIX STREQUAL "/")
  set(_IMPORT_PREFIX "")
endif()

You can also see it on the cjson-<BUILD_TYPE>.cmake Where the IMPORTED_LOCATION_<BUILD_TYPE> will be the FULL path and if using the relative path variables it will just use the calculated _IMPORT_PREFIX instead.

If you want I can make a pull request with this simple fix. 😅

PS. This does not affect CJSON_INCLUDE_DIRS and CJSON_INCLUDE_DIR variables. Those still have the full path.