我最近将我的 C++ 项目的构建系统切换到了 CMake。我正在尝试使用 ExternalProject_Add 函数下载所需的库（目前有 3 个，GLM 和 TINYOBJ 是静态的，GLFW 可以是静态的或动态的），然后在我的项目中链接到它们。我希望能够以最小的努力链接这些库（可能还有其他库），以便我可以在多个平台上构建。或者，如果其他人来参与该项目，他们不必太担心安装正确的库。
但是，在构建时（在带有 MinGW 的 Windows 10 上）我不断收到这些错误：
[100%] Linking CXX executable app\OpenGLTest.exe
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0xd): undefined reference to `FPSCounter::getElapsedTime()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x2b): undefined reference to `FPSCounter::reset()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x54): undefined reference to `FPSCounter::setLastTick()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x5e): undefined reference to `FPSCounter::addFrame()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x12d): undefined reference to `GLCamera::getCameraZoom()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x149): undefined reference to `GLCamera::setCameraZoom(float)'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x1de): undefined reference to `GLCamera::getCameraPosition()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x747): undefined reference to `GLCamera::setCameraTarget(glm::tvec3<float, (glm::precision)0>)'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x771): undefined reference to `GLCamera::setCameraPosition(glm::tvec3<float, (glm::precision)0>)'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0x968): undefined reference to `GLRenderer_Deferred::GLRenderer_Deferred()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0xb98): undefined reference to `FPSCounter::FPSCounter()'
CMakeFiles\OpenGLTest.dir/objects.a(Main.cpp.obj):Main.cpp:(.text+0xba2): undefined reference to `FPSCounter::FPSCounter()'
collect2.exe: error: ld returned 1 exit status
CMakeFiles\OpenGLTest.dir\build.make:98: recipe for target 'app/OpenGLTest.exe' failed
mingw32-make[2]: *** [app/OpenGLTest.exe] Error 1
CMakeFiles\Makefile2:66: recipe for target 'CMakeFiles/OpenGLTest.dir/all' failed
mingw32-make[1]: *** [CMakeFiles/OpenGLTest.dir/all] Error 2
Makefile:126: recipe for target 'all' failed
mingw32-make: *** [all] Error 2
我的目录结构如下所示：
|-Project
|-BUILD (all the CMake output files are here)
| |-app (this is where the .exe is output to)
| |-downloads (dependencies are downloaded here)
| |-deps
|-OpenGL (this is the source directory)
|-deps-CMakeLists.txt
|-CMakeLists.txt
|-src
|-Main.cpp
|-**Other source files and headers of the "undefined reference" errors are in this directory**
|-RenderSystem
|-More Source files
这是我的 CMakeLists.txt：
cmake_minimum_required(VERSION 3.2)
project(OpenGLTest)
set(CMAKE_CXX_FLAGS "-std=c++11")
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/app)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(EX_PROJ_SOURCE_DIR ${CMAKE_BINARY_DIR}/downloads/deps/Source)
set(EX_PROJ_BUILD_DIR ${CMAKE_BINARY_DIR}/downloads/deps/Build)
# Include OpenGL
find_package(OpenGL REQUIRED)
if (OPENGL_FOUND)
include_directories(${OPENGL_INCLUDE_DIR})
endif()
# Include GLEW
find_package(GLEW REQUIRED)
if (GLEW_FOUND)
include_directories(${GLEW_INCLUDE_DIRS})
endif()
set(GLFW_LIB_DIR ${EX_PROJ_BUILD_DIR}/GLFW_EX/src)
link_directories(${GLFW_LIB_DIR})
# Download and unpack gtest at configure time
configure_file(deps-CMakeLists.txt downloads/CMakeLists.txt)
execute_process(COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" . WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/downloads)
execute_process(COMMAND ${CMAKE_COMMAND} --build . WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/downloads)
# Add gtest directly to our build
add_subdirectory(${EX_PROJ_SOURCE_DIR}/GLM_EX
${EX_PROJ_BUILD_DIR}/GLM_EX
EXCLUDE_FROM_ALL )
add_subdirectory(${EX_PROJ_SOURCE_DIR}/GLFW_EX
${EX_PROJ_BUILD_DIR}/GLFW_EX
EXCLUDE_FROM_ALL )
add_subdirectory(${EX_PROJ_SOURCE_DIR}/TINYOBJ_EX
${EX_PROJ_BUILD_DIR}/TINYOBJ_EX
EXCLUDE_FROM_ALL )
# Add the gtest include directory, since gtest
# doesn't add that dependency to its gtest target
include_directories(${EX_PROJ_SOURCE_DIR}/GLM_EX/glm
${EX_PROJ_SOURCE_DIR}/GLFW_EX/include
${EX_PROJ_SOURCE_DIR}/TINYOBJ)
# add the executable
add_executable(OpenGLTest src/Main.cpp)
target_link_libraries(OpenGLTest tinyobjloader glm glfw3 ${GLEW_LIBRARIES} ${OPENGL_LIBRARIES})
add_custom_command(TARGET OpenGLTest POST_BUILD # Adds a post-build event to MyTest
COMMAND ${CMAKE_COMMAND} -E copy_if_different # which executes "cmake - E copy_if_different..."
"${GLFW_LIB_DIR}/glfw3.dll" # <--this is in-file
$<TARGET_FILE_DIR:OpenGLTest>) # <--this is out-file path
这是 deps-CMakeLists.txt 文件：
cmake_minimum_required(VERSION 3.2)
project(deps-download LANGUAGES NONE)
include(ExternalProject)
set_directory_properties(PROPERTIES EP_BASE "./deps")
# Include GLFW
ExternalProject_Add (
GLFW_EX
GIT_REPOSITORY "https://github.com/glfw/glfw.git"
GIT_TAG "master"
CMAKE_ARGS -DGLFW_BUILD_EXAMPLES=OFF
-DGLFW_BUILD_TESTS=OFF
-DGLFW_BUILD_DOCS=OFF
-DGLFW_INSTALL=OFF
-DBUILD_SHARED_LIBS=ON
UPDATE_COMMAND ""
INSTALL_COMMAND ""
TEST_COMMAND "")
# Include GLM
ExternalProject_Add (
GLM_EX
GIT_REPOSITORY "https://github.com/g-truc/glm.git"
GIT_TAG "master"
UPDATE_COMMAND ""
BUILD_COMMAND ""
INSTALL_COMMAND ""
TEST_COMMAND "")
# Include TINYOBJ
ExternalProject_Add (
TINYOBJ_EX
GIT_REPOSITORY "https://github.com/syoyo/tinyobjloader.git"
GIT_TAG "master"
UPDATE_COMMAND ""
BUILD_COMMAND ""
INSTALL_COMMAND ""
TEST_COMMAND "")
add_dependencies(GLFW_EX GLM_EX TINYOBJ_EX)
我的“main”与错误中引用的所有文件一起位于“src”目录中的 Main.cpp 中作为“未定义的引用”。我已经为所有库添加了包含目录（就在 ExternalProject_Add 命令之后），并尝试链接为 GLFW 构建的动态库，但它似乎仍然不起作用。
为了正确构建它，我缺少什么？任何帮助，将不胜感激。
更新：
正如克雷格斯科特所建议的那样，我已经改变了一些东西并将ExternalProject_Add命令移动到另一个文件，该文件在我的构建的配置阶段执行。我已确保所有外部库都已链接。我什至在不同的测试项目中分别测试了每个库，以确保 CMake 文件正常工作。
我得到的所有“未定义引用”都来自我编写的文件，并且在我的源代码树中。他们如何/为什么不被包括在内？
注意：我也尝试过包含“src”目录，但似乎没有做任何事情。