Reply To: STL File not valid
Your initial post in this thread indicated that you get a runtime exception upon executing your program. i.e. the problem in this case is not the build system.
On the topic of build systems: OpenLB uses a plain Makefile for building both the library and any applications / examples and we can not support any custom setup on your side, especially considering that we do not know how exactly you configured your CMakeLists.txt file. Any IDE that supports CMake should have no problem coping with plain Makefiles.
On the topic of your initial problem: Sthavishtha already replied that the problem seems to be where you place the STL file / from which working directory you execute the program. I agree with this assessment. Did you try to switch to the cylinder3d example directory in a terminal and manually execute the executable from there?