引言#

CMake支持以多種不同方式設置編譯標志：

• 使用target_compile_definitions（）函數
• 使用CMAKE_C_FLAGS和CMAKE_CXX_FLAGS變量。

本教程中的文件如下：

$ tree . ├── CMakeLists.txt ├── main.cpp

• [CMakeLists.txt] - 包含要運行的CMake命令

  cmake_minimum_required(VERSION 3.5)# Set a default C++ compile flag set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DEX2" CACHE STRING "Set C++ Compiler Flags" FORCE)# Set the project name project (compile_flags)# Add an executable add_executable(cmake_examples_compile_flags main.cpp)target_compile_definitions(cmake_examples_compile_flags PRIVATE EX3 )

• [main.cpp] - 具有main的源文件

  #include <iostream>int main(int argc, char *argv[]) {std::cout << "Hello Compile Flags!" << std::endl;// only print if compile flag set #ifdef EX2std::cout << "Hello Compile Flag EX2!" << std::endl; #endif#ifdef EX3std::cout << "Hello Compile Flag EX3!" << std::endl; #endifreturn 0; }

概念#

設置每個目標的C++標志#

在現代CMake中設置C++標志的推薦方式是使用每個目標的標志，這些標志可以通過target_compile_definitions()函數的作用域（或者說接口范圍）遞到其他目標（INTERFACE或PUBLIC）。這將填充庫的INTERFACE_COMPILE_DEFINITIONS，并根據作用域將定義傳遞到鏈接的目標。

target_compile_definitions(cmake_examples_compile_flagsPRIVATE EX3 )

這將導致編譯器在編譯目標時添加定義 -DEX3。

如果目標是庫，并且已經選擇了作用域PUBLIC或者INTERFACE，則該定義也將包含在鏈接該目標的任何可執行文件中。

對于編譯器選項，你還可以使用target_compile_options()函數。

設置默認C++標志#

CMAKE_CXX_FLAGS的默認值為空或包含生成類型的相應標志。

要設置其他默認編譯標志，可以將以下內容添加到頂級CMakeLists.txt。

set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DEX2" CACHE STRING "Set C++ Compiler Flags" FORCE)

與CMAKE_CXX_FLAGS類似的其他選項包括：

• 使用CMAKE_C_FLAGS設置 C 編譯器標志
• 使用CMAKE_LINKER_FLAGS設置鏈接器標志

一旦設置，CMAKE_C_FLAGS和CMAKE_CXX_FLAGS將為該目錄或任何包含的子目錄中的所有目標全局設置編譯器標志/定義。現在不建議將此方法用于一般用途，最好使用target_compile_definitions函數。

設置CMake標志#

與構建類型類似，可以使用以下方法設置全局C++編譯器標志。

• 使用GUI工具，如ccmake/cmake-gui

• 傳遞到cmake

cmake .. -DCMAKE_CXX_FLAGS="-DEX3"

構建示例#

$ mkdir build$ cd build/$ cmake .. -- The C compiler identification is GNU 4.8.4 -- The CXX compiler identification is GNU 4.8.4 -- Check for working C compiler: /usr/bin/cc -- Check for working C compiler: /usr/bin/cc -- works -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working CXX compiler: /usr/bin/c++ -- Check for working CXX compiler: /usr/bin/c++ -- works -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- Configuring done -- Generating done -- Build files have been written to: /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build$ make VERBOSE=1 /usr/bin/cmake -H/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags -B/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build --check-build-system CMakeFiles/Makefile.cmake 0 /usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles/progress.marks make -f CMakeFiles/Makefile2 all make[1]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build' make -f CMakeFiles/cmake_examples_compile_flags.dir/build.make CMakeFiles/cmake_examples_compile_flags.dir/depend make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build' cd /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles/cmake_examples_compile_flags.dir/DependInfo.cmake --color= Dependee "/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles/cmake_examples_compile_flags.dir/DependInfo.cmake" is newer than depender "/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles/cmake_examples_compile_flags.dir/depend.internal". Dependee "/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles/CMakeDirectoryInformation.cmake" is newer than depender "/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles/cmake_examples_compile_flags.dir/depend.internal". Scanning dependencies of target cmake_examples_compile_flags make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build' make -f CMakeFiles/cmake_examples_compile_flags.dir/build.make CMakeFiles/cmake_examples_compile_flags.dir/build make[2]: Entering directory `/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build' /usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles 1 [100%] Building CXX object CMakeFiles/cmake_examples_compile_flags.dir/main.cpp.o /usr/bin/c++ -DEX2 -o CMakeFiles/cmake_examples_compile_flags.dir/main.cpp.o -c /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/main.cpp Linking CXX executable cmake_examples_compile_flags /usr/bin/cmake -E cmake_link_script CMakeFiles/cmake_examples_compile_flags.dir/link.txt --verbose=1 /usr/bin/c++ -DEX2 CMakeFiles/cmake_examples_compile_flags.dir/main.cpp.o -o cmake_examples_compile_flags -rdynamic make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build' /usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles 1 [100%] Built target cmake_examples_compile_flags make[1]: Leaving directory `/home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build' /usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/01-basic/G-compile-flags/build/CMakeFiles 0

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