Dear group,
I'm new to CMake and read all related tutorials that I could find and
the Mastering CMake book (I didn't get very far) and watched Daniel
Pfeifer's talk. Unfortunately, I'm afraid that I still cannot figure out
a couple of apparently simple things, especially in today's "best
practices" style.
Please consider:
find_package(JPEG REQUIRED)
At first, this didn't work for me under Ubuntu Linux, because I didn't
have the libjpeg-dev package installed. The error message was:
CMake Error at
/usr/share/cmake-3.9/Modules/FindPackageHandleStandardArgs.cmake:137
(message):
Could NOT find JPEG (missing: JPEG_LIBRARY JPEG_INCLUDE_DIR)
Call Stack (most recent call first):
/usr/share/cmake-3.9/Modules/FindPackageHandleStandardArgs.cmake:377
(_FPHSA_FAILURE_MESSAGE)
/usr/share/cmake-3.9/Modules/FindJPEG.cmake:30
(FIND_PACKAGE_HANDLE_STANDARD_ARGS)
Libs/CMakeLists.txt:5 (find_package)
Well, I provoked this intentionally for learning and testing, but if I
hadn't been prepared, from the error message alone I would not have
known how to proceed. `sudo apt install libjepg-dev` fixed the problem.
Now I'm under Windows, Visual Studio Community 2017. Same error message,
and obviously no solution as easy as `sudo apt ...`.
It's quite clear that I have to add the libjpeg source code as a
subfolder to my project and compile it as part of the main project. But,
starting with the above `find_package(JPEG REQUIRED)`, how is this
properly done?
Generalizing my question:
I started with `find_package(JPEG REQUIRED)` as shown above in order to
the find the JPEG library that comes preinstalled with the system.
How do I deal with the following scenarios?
- libjpeg is theoretically available, but just not installed in the
system (that is, `sudo apt install libjpeg-dev` would help)?
- libjpeg is available in the system, but the version is too new or
too old?
- libjpeg is not available in the system at all (e.g. Windows)?
- As a fallback, in the case that any of the above checks is
negative, it seems that there is no alternative but to ship and compile
a copy of libjpeg along with my project: How is this properly expressed
in my project's CMakeLists.txt? Daniel mentioned something about the
behavior of `find_package()` in his talk, but I'm afraid that I still
cannot come up with a proper solution.
Best regards,
Carsten
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