CMake中set_property设置COMPILE_FLAGS时分号替代空格问题解决

问题场景 #

为文件夹内部分C文件设置特殊编译选项，尝试用set_property的两种方式配置（列表定义、直接写入），但生成的Make命令中编译选项被分号分隔，导致编译异常：

原始CMake代码 #

cmake_minimum_required(VERSION 3.16)

file(GLOB_RECURSE all_sources "./*.c" "./*.S")

set(CURRENT_LIB_NAME my_c_library)
enable_language(ASM)
set(c_flags
    -msse4.1
    # some other flags
)

set(c_sandybridge_flags
    -O2
    -march=sandybridge
    -mtune=sandybridge
)
file(GLOB SANDYBRIDGE_SRC_FILES
    "*_slow.c"
    "*_dispatcher.c"
    "arion.c"
)
set_property(SOURCE ${SANDYBRIDGE_SRC_FILES} PROPERTY COMPILE_FLAGS ${c_sandybridge_flags})

file(GLOB HASWELL_SRC_FILES
    "./*_ab2.c"
)
set_property(SOURCE ${HASWELL_SRC_FILES} PROPERTY COMPILE_FLAGS -O2 -mavx2 )

add_compile_options(
    "$<$<COMPILE_LANGUAGE:C>:${c_flags}>"
)

add_library(${CURRENT_LIB_NAME} STATIC
    ${all_sources}
)

target_include_directories(${CURRENT_LIB_NAME} PRIVATE ${PROJECT_SOURCE_DIR}/mylibrary/include)

生成的错误编译命令示例 #

/usr/bin/clang -Isomeinclude -msse4.1 -O2;-march=sandybridge;-mtune=sandybridge -MD -MT CMakeFiles/c_file.c.o -MF CMakeFiles/c_file.c.o.d -o CMakeFiles/c_file.c.o -c lib/c_file.c

问题原因 #

CMake的COMPILE_FLAGS属性接收的是单个字符串，而非列表。当直接传入列表变量（如${c_sandybridge_flags}）时，CMake会将列表元素用分号拼接成字符串；直接写多个参数（如-O2 -mavx2）时，会被识别为多个列表元素，最终同样被分号连接。

解决方法 #

1. 列表定义的编译选项：转为空格分隔字符串 #

使用CMake的$<JOIN:...>生成器表达式，将列表元素用空格连接后传入：

set_property(SOURCE ${SANDYBRIDGE_SRC_FILES} PROPERTY COMPILE_FLAGS "$<JOIN:${c_sandybridge_flags}, >")

或者提前用string(JOIN)处理列表：

string(JOIN " " c_sandybridge_flags_str ${c_sandybridge_flags})
set_property(SOURCE ${SANDYBRIDGE_SRC_FILES} PROPERTY COMPILE_FLAGS ${c_sandybridge_flags_str})

2. 直接写入的编译选项：包裹为单个字符串 #

将多个编译选项放在双引号内，作为单个字符串传递：

set_property(SOURCE ${HASWELL_SRC_FILES} PROPERTY COMPILE_FLAGS "-O2 -mavx2")

修改后的完整CMake代码 #

cmake_minimum_required(VERSION 3.16)

file(GLOB_RECURSE all_sources "./*.c" "./*.S")

set(CURRENT_LIB_NAME my_c_library)
enable_language(ASM)
set(c_flags
    -msse4.1
    # some other flags
)

set(c_sandybridge_flags
    -O2
    -march=sandybridge
    -mtune=sandybridge
)
file(GLOB SANDYBRIDGE_SRC_FILES
    "*_slow.c"
    "*_dispatcher.c"
    "arion.c"
)
# 使用JOIN将列表转为空格分隔字符串
set_property(SOURCE ${SANDYBRIDGE_SRC_FILES} PROPERTY COMPILE_FLAGS "$<JOIN:${c_sandybridge_flags}, >")

file(GLOB HASWELL_SRC_FILES
    "./*_ab2.c"
)
# 直接将选项包裹为单个字符串
set_property(SOURCE ${HASWELL_SRC_FILES} PROPERTY COMPILE_FLAGS "-O2 -mavx2")

add_compile_options(
    "$<$<COMPILE_LANGUAGE:C>:${c_flags}>"
)

add_library(${CURRENT_LIB_NAME} STATIC
    ${all_sources}
)

target_include_directories(${CURRENT_LIB_NAME} PRIVATE ${PROJECT_SOURCE_DIR}/mylibrary/include)

内容的提问来源于stack exchange，提问作者Tomáš Zato