Multiple CMakeLists

Question

Suppose I have a directory structure as follows:

/main.cpp
/CMakeLists.txt
/foo/foo.cpp
/foo/CMakeLists.txt

where my /CMakeLists.txt<

Answer 1

Does it search for a second CMakeLists.txt file in foo

Yes, it does

and add the contents to the first?

No it doesn't. It performs a number of configuring actions such as finding libraries etc and a generates separate Makefile and/or other build-time artifacts.

And specifically in this example, will the variable ${OpenNI_LIB} be recognised in the first, given that it is defined in the second?

no, unless such a construction

find_library(OpenNI REQUIRED) # this sets variables for OpenNI
                              # in the context of foo/CMakeLists.txt
set(OpenNI_LIB ${OpenNI_LIB} PARENT_SCOPE) # this copies ${OpenNI_LIB}
                              # into the context of /CMakeLists.txt

is used in foo/CMakeLists.txt

By default variables defined in a subdirectory's CMakeLists.txt are also defined in the subdirectory's subdirectories, that is if foo/ in turn contained bar/ with its own CMakeLists.txt, then within bar/'s CMakeLists.txt ${OpenNI_LIB} would be set.

P.S. message(STATUS "Some message with ${VAR}") in doubtful places of CMakeLists.txt is your friend. Just look into cmake output.