这似乎是一个琐碎的问题，因为CMake是一种脚本语言，通常的答案是：严格按照顺序进行。但我遇到了几种情况，在这些情况下，CMake解析某些文件的顺序很重要。所以我想知道：
当我运行例如
- 是否有可用的文档描述文件（包括内部CMake文件）解析的顺序？
- 文件顺序是否取决于CMake版本或某些CMake选项/设置/环境，包括所选生成器或主机环境？
迄今为止，我遇到过以下情况，其中上述信息很重要：
- 在识别编译器之前解析工具链文件，因此您必须首先/在工具链文件中填充某些CMake变量：使用特定链接器进行CMake交叉编译不会将参数传递给armlink
- 工具链文件被多次解析，因此来自工具链文件的打印消息显示多次：CMake工具链包含多个文件
- 变量监视可以从已解析您的主
CMakeLists.txt文件之外的范围调用：在“配置”步骤完成之前作为最后一步在CMake中执行命令或宏
也许你知道更多。
为了找到答案，我尝试了以下方法：我设置了一个简单的主要CMakeLists.txt，如下所示，并运行cmake --trace …来分析解析顺序。
cmake_minimum_required(VERSION 2.8)
include(BeforeProjectCmd.cmake)
project(ParserTest CXX)
add_subdirectory(LibTarget1)
add_subdirectory(LibTarget2)
add_executable(ExeTarget Test.cpp)
variable_watch(CMAKE_BACKWARDS_COMPATIBILITY)
当我运行例如
cmake --debug-output --trace -G"Visual Studio 12 2013" -DCMAKE_TOOLCHAIN_FILE:FILE_PATH=Toolchain.txt时，我得到了一个很长的跟踪信息，我试图总结一下：# Begin try to read
CMakeCache.txt
${CMAKE_BINARY_DIR}/CMakeCache.txt
PreLoad.cmake
${CMAKE_BINARY_DIR}/PreLoad.cmake
# End try to read
┌ CMakeLists.txt(1): cmake_minimum_required(VERSION 2.8 )
│ CMakeLists.txt(3): include(BeforeProjectCmd.cmake )
│
├─ BeforeProjectCmd.cmake
│
│ CMakeLists.txt(5): project(ParserTest CXX )
├┬ share/cmake-3.2/Modules/CMakeDetermineSystem.cmake
││
│└─ Toolchain.txt
│
├┬ ${CMAKE_PLATFORM_INFO_DIR}/CMakeSystem.cmake
││
│└─ Toolchain.txt
│
├─ share/cmake-3.2/Modules/CMakeSystemSpecificInitialize.cmake
├┬ share/cmake-3.2/Modules/CMakeDetermineCXXCompiler.cmake
│├┬ share/cmake-3.2/Modules/CMakeDetermineCompiler.cmake
││├ share/cmake-3.2/Modules/Platform/Windows-CXX.cmake
…
││├ share/cmake-3.2/Modules/CMakeDetermineCompilerId.cmake
││├─ share/cmake-3.2/Modules/CMakeCompilerIdDetection.cmake
…
││├ share/cmake-3.2/Modules/Compiler/MSVC-DetermineCompiler.cmake
…
│├ ${CMAKE_BINARY_DIR}/${CMAKE_FILES_DIRECTORY}/3.2.2/CMakeCXXCompiler.cmake
│├ share/cmake-3.2/Modules/CMakeSystemSpecificInformation.cmake
│├┬ share/cmake-3.2/Modules/CMakeGenericSystem.cmake
││├ share/cmake-3.2/Modules/Platform/Windows.cmake
││└─ share/cmake-3.2/Modules/Platform/WindowsPaths.cmake
│├ share/cmake-3.2/Modules/CMakeCXXInformation.cmake
│├┬ share/cmake-3.2/Modules/Compiler/MSVC-CXX.cmake
││├ share/cmake-3.2/Modules/Platform/Windows-MSVC-CXX.cmake
││├┬ share/cmake-3.2/Modules/Platform/Windows-MSVC.cmake
│││└─ share/cmake-3.2/Modules/CMakeRCInformation.cmake
││└ share/cmake-3.2/Modules/CMakeCommonLanguageInclude.cmake
│├ share/cmake-3.2/Modules/CMakeTestCXXCompiler.cmake
│├┬ share/cmake-3.2/Modules/CMakeTestCompilerCommon.cmake
││├ share/cmake-3.2/Modules/CMakeDetermineCompilerABI.cmake
││├ share/cmake-3.2/Modules/CMakeDetermineCompileFeatures.cmake
││├ share/cmake-3.2/Modules/Internal/FeatureTesting.cmake
││└ share/cmake-3.2/Modules/Compiler/MSVC-CXX-FeatureTests.cmake
│└ ${CMAKE_BINARY_DIR}/${CMAKE_FILES_DIRECTORY}/3.2.2/CMakeCXXCompiler.cmake
│
│ CMakeLists.txt(7): add_subdirectory(LibTarget1 )
│
├─ LibTarget1/CMakeLists.txt
│
│ CMakeLists.txt(8): add_subdirectory(LibTarget2 )
│
├─ LibTarget2/CMakeLists.txt
│
│ CMakeLists.txt(10): add_executable(ExeTarget Test.cpp )
│ CMakeLists.txt(12): variable_watch(CMAKE_BACKWARDS_COMPATIBILITY )
│
│ CMake Debug Log in CMakeLists.txt:
│ Variable "CMAKE_BACKWARDS_COMPATIBILITY" was accessed using UNKNOWN_READ_ACCESS with value "".
-- Configuring done
-- Generating ${CMAKE_BINARY_DIR}
-- Generating ${CMAKE_BINARY_DIR}/LibTarget1
-- Generating ${CMAKE_BINARY_DIR}/LibTarget2
-- Generating done
# Writes
${CMAKE_BINARY_DIR}/CMakeCache.txt
看到上面的输出，我得出了以下结论（我希望这些结论是正确的并且有些通用）：
CMakeCache.txt文件只在配置启动时读取一次，并在生成完成后写入。它仅保留“全局变量”缓存的状态。project()命令触发了大部分 CMake 的检测魔法（包括从Toolchain.txt文件中读取）。- 工具链文件被读取两次。一次是在检测到编译系统之前，另一次是在生成的
CMakeSystem.cmake中。 variable_watch()钩子可以随时触发，因此调用最佳“执行命令”的范围未定义。