<html><head></head><body><div>Dear CMake users,</div><div><br></div><div>Maybe my question is trivial for most, but still I do not find an answer on my own!</div><div><br></div><div>If you have a project and some sub-project (or module or whatever the jargon is) that are both managed with CMake, they should be in separate directories (directory trees), and each of them have a CMakeLists.txt in the root directory, where the sub-project is "included" into the main project with an ADD_DIRECTORY() etc. So far so clear.</div><div><br></div><div>But then I learned that it is good practice to ensure that the sub-project would also be "buildable" with cmake separately. My problem is about how to pass options from the main to the sub project in such a way that this is working properly, i.e.:</div><div><br></div><div>- if the sub project is part of the main project it would simply take over the option from the main project level</div><div>- but if the sub project is being built standalone, the option is not defined and should be set e.g. in cmake-gui</div><div><br></div><div>If I write now in the sub project</div><div><br></div><div>IF(THAT_OPTION)</div><div> ...</div><div><br></div><div>this will be true if THAT_OPTION was set to ON in the main project. So far so good. But the expression is now so "clever" that it cannot distinguish between THAT_OPTION being set to OFF in the main project, or THAT_OPTION not being defined at all - like in a standalone build!</div><div><br></div><div>One way would be to have an additional option or variable BUILDING_MAINPROJECT which is set to ON or TRUE in the main project and can be checked. However, I have so far not seen any CMakeLists.txt with such a code, so ... what are the experts doing in such a case?</div><div><br></div><div>Thanks and regards,</div><div>Cornelis</div><div></div></body></html>