我有许多使用CMake构建的项目，我希望能够轻松地在使用GCC或Clang/LLVM之间切换来编译它们。我相信(如果我弄错了请纠正我!)使用Clang我需要设置以下:
SET (CMAKE_C_COMPILER "/usr/bin/clang")
SET (CMAKE_C_FLAGS "-Wall -std=c99")
SET (CMAKE_C_FLAGS_DEBUG "-g")
SET (CMAKE_C_FLAGS_MINSIZEREL "-Os -DNDEBUG")
SET (CMAKE_C_FLAGS_RELEASE "-O4 -DNDEBUG")
SET (CMAKE_C_FLAGS_RELWITHDEBINFO "-O2 -g")
SET (CMAKE_CXX_COMPILER "/usr/bin/clang++")
SET (CMAKE_CXX_FLAGS "-Wall")
SET (CMAKE_CXX_FLAGS_DEBUG "-g")
SET (CMAKE_CXX_FLAGS_MINSIZEREL "-Os -DNDEBUG")
SET (CMAKE_CXX_FLAGS_RELEASE "-O4 -DNDEBUG")
SET (CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g")
SET (CMAKE_AR "/usr/bin/llvm-ar")
SET (CMAKE_LINKER "/usr/bin/llvm-ld")
SET (CMAKE_NM "/usr/bin/llvm-nm")
SET (CMAKE_OBJDUMP "/usr/bin/llvm-objdump")
SET (CMAKE_RANLIB "/usr/bin/llvm-ranlib")
是否有一种简单的方法在这些和默认的GCC变量之间切换，最好是作为一个系统范围的更改，而不是特定于项目(即不只是将它们添加到项目的CMakeLists.txt)?
另外，当使用clang而不是gcc编译时，是否有必要使用llvm-*程序而不是系统默认值?有什么不同?
根据cmake的帮助:
-C <initial-cache>
Pre-load a script to populate the cache.
When cmake is first run in an empty build tree, it creates a CMakeCache.txt file and populates it with customizable settings for the project. This option may be used to specify a file from
which to load cache entries before the first pass through the project's cmake listfiles. The loaded entries take priority over the project's default values. The given file should be a CMake
script containing SET commands that use the CACHE option, not a cache-format file.
你可以创建像gcc_compiler.txt和clang_compiler.txt这样的文件，以包含CMake语法中的所有相关配置。
Clang Example (clang_compiler.txt):
set(CMAKE_C_COMPILER "/usr/bin/clang" CACHE string "clang compiler" FORCE)
然后运行它
GCC:
cmake -C gcc_compiler.txt XXXXXXXX
铛：
cmake -C clang_compiler.txt XXXXXXXX
根据cmake的帮助:
-C <initial-cache>
Pre-load a script to populate the cache.
When cmake is first run in an empty build tree, it creates a CMakeCache.txt file and populates it with customizable settings for the project. This option may be used to specify a file from
which to load cache entries before the first pass through the project's cmake listfiles. The loaded entries take priority over the project's default values. The given file should be a CMake
script containing SET commands that use the CACHE option, not a cache-format file.
你可以创建像gcc_compiler.txt和clang_compiler.txt这样的文件，以包含CMake语法中的所有相关配置。
Clang Example (clang_compiler.txt):
set(CMAKE_C_COMPILER "/usr/bin/clang" CACHE string "clang compiler" FORCE)
然后运行它
GCC:
cmake -C gcc_compiler.txt XXXXXXXX
铛：
cmake -C clang_compiler.txt XXXXXXXX
您可以使用option命令:
option(USE_CLANG "build application with clang" OFF) # OFF is the default
然后将clang-compiler设置包在if()中:
if(USE_CLANG)
SET (...)
....
endif(USE_CLANG)
通过这种方式，它将在gui配置工具中显示为cmake选项。
当然，要使其成为系统范围，您可以使用一个环境变量作为默认值，或者沿用Ferruccio的答案。
Ubuntu系统范围内的C更改:
Sudo update-alternatives——config cc
Ubuntu上系统范围的c++更改:
Sudo update-alternatives——config c++
对于以上每一个，按选择号码(1)和Enter选择Clang:
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/bin/gcc 20 auto mode
1 /usr/bin/clang 10 manual mode
2 /usr/bin/gcc 20 manual mode
Press enter to keep the current choice[*], or type selection number:
