CMake基礎 第7節 編譯標志

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 EX2
    std::cout << "Hello Compile Flag EX2!" << std::endl;
  #endif
  
  #ifdef EX3
    std::cout << "Hello Compile Flag EX3!" << std::endl;
  #endif
  
     return 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，並根據作用域將定義傳遞到鏈接的目標。

target_compile_definitions(cmake_examples_compile_flags
    PRIVATE 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，並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。

對於編譯器選項，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

Note	上述命令中的值 CACHE STRING "Set C++ Compiler Flags" FORCE 用於強制在CMakeCache.txt文件中設置此變量。有關更多詳細信息，請參閱此處。

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於一般用途，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