Why does CMake fail to link my static library? - c++

Question

I am trying to link a static library which I have compiled from the assimp source to my executable CMake project so that it does not have to compile assimp as often since it's such a large library.
I compiled it using CMake with the following commands:
git clone https://github.com/assimp/assimp/
cd assimp
mkdir build
cd build
cmake -DBUILD_SHARED_LIBS=OFF ../CMakeLists.txt
cmake --build .
My project structure looks like this:
.
OpenGL
├── OpenGL
│ ├── res
│ ├── src
│ | └── (my .cpp and .h files)
│ └── CMakeLists.txt
├── libraries
│ └── glfw, glew, imgui...
└── CMakeLists.txt
I now copy assimp/include and assimp/build/bin/Debug/config.h to OpenGL/libraries/assimp/include,
then assimp/build/lib/Debug to OpenGL/libraries/assimp/lib
My CMakeLists.txt(s) look like this:
cmake_minimum_required(VERSION 3.8)
project(OpenGL LANGUAGES CXX C)
set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_FIND_DEBUG_MODE)
if (NOT MSVC)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -msse4.1")
endif()
if (CMAKE_BUILD_TYPE STREQUAL Debug)
add_definitions(-DDEBUG) # preprocessor macro
else()
if (MSVC)
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /SUBSYSTEM:WINDOWS /ENTRY:mainCRTStartup") # if running on release mode remove the cmd prompt on windows
endif()
endif()
add_subdirectory(OpenGL)
add_subdirectory(libraries/glfw)
add_subdirectory(libraries/glew)
add_subdirectory(libraries/nativefiledialog)
target_include_directories(${PROJECT_NAME} PRIVATE
${CMAKE_CURRENT_SOURCE_DIR}/libraries/glfw/include
${CMAKE_CURRENT_SOURCE_DIR}/libraries/glew/include
OpenGL/src
libraries
libraries/stb
libraries/assimp/include
libraries/nativefiledialog/src/include
)
and
cmake_minimum_required(VERSION 3.8)
file(GLOB_RECURSE OpenGL_sources *.cpp ../libraries/imgui/*.cpp ../libraries/stb/*.cpp)
add_executable(${PROJECT_NAME} ${OpenGL_sources} "src/engine/input/Key.cpp" "src/engine/input/Buttons.h" "src/engine/input/Button.h" "src/engine/input/Button.cpp" "src/engine/input/MouseButton.h" "src/engine/input/MouseButton.cpp" "src/engine/rendering/objects/Model.h" "src/engine/rendering/objects/Model.cpp")
target_link_libraries(${PROJECT_NAME} PUBLIC
glfw
libglew_static
${CMAKE_SOURCE_DIR}/libraries/assimp/lib/assimp-vc143-mtd.lib
nativefiledialog
)
or
cmake_minimum_required(VERSION 3.8)
add_library( assimp STATIC IMPORTED )
set_property( TARGET assimp PROPERTY IMPORTED_LOCATION ${CMAKE_SOURCE_DIR}/libraries/assimp/lib/assimp-vc143-mtd.lib)
file(GLOB_RECURSE OpenGL_sources *.cpp ../libraries/imgui/*.cpp ../libraries/stb/*.cpp)
add_executable(${PROJECT_NAME} ${OpenGL_sources} "src/engine/input/Key.cpp" "src/engine/input/Buttons.h" "src/engine/input/Button.h" "src/engine/input/Button.cpp" "src/engine/input/MouseButton.h" "src/engine/input/MouseButton.cpp" "src/engine/rendering/objects/Model.h" "src/engine/rendering/objects/Model.cpp")
target_link_libraries(${PROJECT_NAME} PUBLIC
glfw
libglew_static
assimp
nativefiledialog
)
(Both configurations give the same error)
Running cmake .. from OpenGL/build successfully completes which I think means that CMake was able to find the assimp library.
Now when I run cmake --build . I am greeted with the following error.
assimp-vc143-mtd.lib(AssbinLoader.obj) : error LNK2019: unresolved external symbol uncompress referenced in function "public: virtual void __cdecl Assimp::AssbinImporter::InternReadFile(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,struct aiScene *,class Assimp::IOSystem *)" (?InternReadFile#AssbinImporter#Assimp##UEAAXAEBV?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std##PEAUaiScene##PEAVIOSystem#2##Z) [F:\dev\cpp\OpenGL\build\OpenGL\OpenGL.vcxproj]
assimp-vc143-mtd.lib(Compression.obj) : error LNK2019: unresolved external symbol inflate referenced in function "public: unsigned __int64 __cdecl Assimp::Compression::decompress(void const *,unsigned __int64,class std::vector<char,class std::allocator<char> > &)" (?decompress#Compression#Assimp##QEAA_KPEBX_KAEAV?$vector#DV?$allocator#D#std###std###Z) [F:\dev\cpp\OpenGL\build\OpenGL\OpenGL.vcxproj]
etc...
I believe this means that the function bodies were not found which should be compiled within the .lib.
How do I successfully link the library?

Answer 1

These functions (uncompress and inflate) belong to the ZLIB library. Although assimp CMake links ZLIB in order to use it - which is enough to build assimp by itself, you have to link ZLIB directly to your executable as well in order to use it in your executable context.