c++ - 为什么 CMake 生成不带 CMAKE_CXX_FLAGS 的 Makefile？

Question

这是我的完整 CMakeLists.txt 文件:

set(CMAKE_BUILD_TYPE Release)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wshadow")

set(PROJECT sample)
project(${PROJECT})

set(HEADERS
    Main.h
)
set(SOURCES 
    Main.cpp
)

# Add souce file to project for compile
add_executable (${PROJECT} ${HEADERS} ${SOURCES})

target_link_libraries( ${PROJECT} )

但是，在 Makefile 中，我不会从 CMAKE_CXX_FLAGS 中寻找子字符串“-Wall”和其他选项。

为什么？

Answer 1

CMAKE_CXX_FLAGS 变量最初是使用 project() 命令设置的。在 project() 命令之后移动 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ...")。

来自 CMake Toolchains - Languages文档:

Languages are enabled by the project() command. Language-specific built-in variables, such as CMAKE_CXX_COMPILER, CMAKE_CXX_COMPILER_ID etc are set by invoking the project() command. If no project command is in the top-level CMakeLists file, one will be implicitly generated. By default the enabled languages are C and CXX.

引用资料

• CMake and Make need to be run twice in order to build code successfully
• CMake: In which Order are Files parsed (Cache, Toolchain, …)?