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I have two projects PROJ in my workspace ws with corresponding third party libraries TPL as shown below. All depend on opencv 4.4.

ws   
├── PROJ1 (opencv 4.4)
|    └── TPL1 (opencv 4.4)  
└── PROJ2 (opencv 4.4)
    └── TPL2 (opencv 4.4)

PROJ1, PROJ2 and TPL1 have following lines in their CMakeLists.txt:

set(OpenCV_DIR $ENV{OPENCV4_DIR})
find_package(OpenCV 4.4 REQUIRED)

Whereas TPL2 only have:

find_package(OpenCV 4.4 REQUIRED)

but does not have

set(OpenCV_DIR $ENV{OPENCV4_DIR})

When I run cmake and make inside PROJ1/build and PROJ2/build they succeessbully get built. However, notice that PROJ2 gets built without TPL2 having set(OpenCV_DIR $ENV{OPENCV4_DIR}) specified in its CMakeLists.txt, but TPL1 needs to have this line for PROJ1 to build successfully. Otherwise it gives following error:

fatal error: opencv/cv.h: No such file or directory
26 | #include <opencv/cv.h>
   |          ^~~~~~~~~~~~~

Why is it so? Is there some CMakeLists.txt config that lets third party apps to inherit paths from CMakeLists.txt in parent directories or something similar?

PS: I do not do make install in any of these PROJs and TPLs.

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  • "Is there some CMakeLists.txt config that lets third party apps to inherit paths from CMakeLists.txt in parent directories or something similar?" - What "paths" you are talking about? Variables like OpenCV_DIR are inherited from the parent's CMakeLists.txt automatically. But those variables should be used by the inner project. E.g. by find_package (and following target_link_libraries), or by target_include_directories, or by some other means. Please, provide more code of your projects (preferably in a form of minimal reproducible example). Currently provided code and error message are vague. Commented Oct 14, 2023 at 16:38
  • Ok I edited question to make it more clear. Both TPL1 and TPL2 CMakeLists.txt have find_package(OpenCV 4.4 REQUIRED) . But, TPL1 needs to specify set(OpenCV_DIR $ENV{OPENCV4_DIR}) in its CMakeLists.txt for it to build successfully, whereas TPL2 gets build successfully without needing to have set(OpenCV_DIR $ENV{OPENCV4_DIR}) in its CMakeLists.txt. Somehow TPL1 is unable to inherit set(OpenCV_DIR $ENV{OPENCV4_DIR}) from its parent's CMakeLists.txt but TPL2 is able to inherit it from its parent's CMakeLists.txt. Why this might be happening? Commented Oct 15, 2023 at 14:52
  • "Why this might be happening?" - Without viewing the code, we could only speculate about possible reasons. It could be that variable OpenCV_DIR is modified by some other code in your project (you could use variable_watch command for debug such situation). Or it could be that TPL2 project is included into PROJ2 via add_subdirectory command, and that command is issued before setting the variable (set(OpenCV_DIR $ENV{OPENCV4_DIR})). Commented Oct 15, 2023 at 15:12
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