为什么 CMake COMPILER_DEFINITIONS 不传播到子目录？

Question

根据set_directory_properties 文档，目录上设置的属性应该传播到子目录：

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设置当前目录和子目录的属性。

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根据支持的属性文档，COMPILE_DEFINITIONS 是目录支持的属性。

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鉴于此，为什么目录的 COMPILE_DEFINITIONS 不传播到以下示例中的子目录？

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示例项目文件结构

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- CMakeLists.txt\n- sub\n   -CMakeLists.txt\n   -main.cpp\n

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文件内容

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根 CMakeLists.txt：

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cmake_minimum_required(VERSION 2.8.11)\nproject(cmake_sandbox)\nadd_subdirectory(sub)\nset_directory_properties(PROPERTIES COMPILE_DEFINITIONS SHOW_MESSAGE=1)\n

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子 CMakeLists.txt：

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add_executable(hello main.cpp)\n

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主要.cpp：

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#include <iostream>\nusing namespace std;\n\nint main()\n{\n    #define A_LOCAL_MESSAGE\n    #ifdef A_LOCAL_MESSAGE\n    #pragma message("A local message!")\n    #else\n    #pragma message("No local message!")\n    #endif\n\n    #ifdef SHOW_MESSAGE\n    #pragma message("A message!")\n    #else\n    #pragma message("No message!")\n    #endif\n    cout << "Hello, World!\\n";\n    return 0;\n}\n

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测试

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$ cmake --version\ncmake version 3.10.2\n\nCMake suite maintained and supported by Kitware (kitware.com/cmake).\n$ rm -rf build && mkdir build && cd build && cmake .. && make -j && sub/hello\n-- The C compiler identification is GNU 7.4.0\n-- The CXX compiler identification is GNU 7.4.0\n-- Check for working C compiler: /usr/bin/cc\n-- Check for working C compiler: /usr/bin/cc -- works\n-- Detecting C compiler ABI info\n-- Detecting C compiler ABI info - done\n-- Detecting C compile features\n-- Detecting C compile features - done\n-- Check for working CXX compiler: /usr/bin/c++\n-- Check for working CXX compiler: /usr/bin/c++ -- works\n-- Detecting CXX compiler ABI info\n-- Detecting CXX compiler ABI info - done\n-- Detecting CXX compile features\n-- Detecting CXX compile features - done\n-- Configuring done\n-- Generating done\n-- Build files have been written to: /home/caleb/src/cmake-sandbox/build\nScanning dependencies of target hello\n[ 50%] Building CXX object sub/CMakeFiles/hello.dir/main.cpp.o\n/home/caleb/src/cmake-sandbox/sub/main.cpp: In function \xe2\x80\x98int main()\xe2\x80\x99:\n/home/caleb/src/cmake-sandbox/sub/main.cpp:8:36: note: #pragma message: A local message!\n  #pragma message("A local message!")\n                                    ^\n/home/caleb/src/cmake-sandbox/sub/main.cpp:16:31: note: #pragma message: No message!\n  #pragma message("No message!")\n                               ^\n[100%] Linking CXX executable hello\n[100%] Built target hello\nHello, World!\n

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如果在根级别设置的 COMPILE_DEFINITION 已按预期传播，则第二个编译指示输出将更改为“一条消息！” 案件。为什么这没有发生？

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Answer 1

add_subdirectory使 CMake 进入子目录并处理其中的 CMakeLists.txt 文件，然后再处理后面的指令add_subdirectory。

如果您希望采用这些设置，则需要在递归到子目录之前设置它们。

set_directory_properties(PROPERTIES COMPILE_DEFINITIONS SHOW_MESSAGE=1)
add_subdirectory(sub)