What's the shape of CMake library when using find_library() - c++

Question

What is the file structure of CMake library?
For example, here is my library located in library folder:
library
\mylib1.so
\mylib2.so
The headers are in other dir out of library.
Can I use find_library(mylib1 PATHS library) to find my library and use target_include_directories() or include_directories() to include my headers? For my testing, it's failed. So what's the right structure?
Do I need put the header files (.h or .hpp) into library/include folder and put .so in lib folder or put them all into the library folder?
I didn't find any explain in CMake documents. I also find other commands in CMake documents but they are lack of something in details that I don't understand. So I'd like to known how do I find the documents like this.

Answer 1

find_library is used to find a file, but it doesn't create identify provide any information about include directories or other information required by the linking target.
To be able to use your lib after installing it's best to make use of find_package.
You could place files like into a install directory MyLibrary like this:
MyLibrary/lib/MyLib-0.1.1/MyLibraryConfig.cmake
MyLibrary/lib/MyLib-0.1.1/MyLibraryConfigVersion.cmake
MyLibrary/lib/MyLib-0.1.1/libmylibrary.so
MyLibrary/include/MyLib-0.1.1/include/...
MyLibraryConfigVersion.cmake
This file is used to check, if the version of the library is compatible with the build configuration of the project using find_package. Additionaly it provides cmake with information about the version of the library:
set(PACKAGE_VERSION 0.1.1)
if(NOT UNIX # must be the same target platform
OR NOT CMAKE_SIZEOF_VOID_P EQUAL 8 # assuming the installed lib is 64 bit
OR PACKAGE_VERSION VERSION_LESS PACKAGE_FIND_VERSION)
set(PACKAGE_VERSION_COMPATIBLE FALSE) # inform find_package this is not a suitable version of the lib
else()
set(PACKAGE_VERSION_COMPATIBLE TRUE)
if(PACKAGE_FIND_VERSION STREQUAL PACKAGE_VERSION)
set(PACKAGE_VERSION_EXACT TRUE)
endif()
endif()
MyLibraryConfig.cmake
This file is used to actually create the imported lib to use by the project calling find_package; It's only included, if the version file considers the configuration suitable.
if (NOT TARGET MyLibrary) # avoid issues with using find_package(MyLibrary) multiple times
add_library(MyLibrary IMPORTED)
# provide the necessary info about the target
set_target_properties(MyLibrary PROPERTIES
IMPORTED_LOCATION "${CMAKE_CURRENT_LIST_DIR}/libmylibrary.so" # specify absolute library file location using the directory containing this cmake file
)
target_include_directories(MyLibrary INTERFACE "${CMAKE_CURRENT_LIST_DIR}/../../include/MyLib-0.1.1/include")
endif()
This allows you to "tell" cmake about the location of the install dir and use find_package like this:
list(APPEND CMAKE_PREFIX_PATH /path/to/MyLibrary) # this could be passed via -D option during configuration instead
find_package(MyLibrary REQUIRED)
Note that there are alternative paths where to put the cmake configuration files, see the documentation of find_package. Furthermore there is cmake functionality that can take over generating some, if not all of the cmake configuration files for you automatically on installation, see
install()
The CMakePackageConfigHelpers cmake module