build - 带有 set_target_properties 的 FindPkgConfig 无法用于设置 CFLAGS/LDFLAGS

Question

FindPkgConfig 中的

pkg_check_modules 给出 MYLIBRARY_LDFLAGS 和 MYLIBRARY_CFLAGS 是普通的 CMake 列表(带分号分隔符)。

set_target_properties 和 set_property 只接受一个字符串。

所以这不起作用，因为它没有扩展列表:

set_property(TARGET ${PROJECT_NAME} APPEND PROPERTY LINK_FLAGS ${MYLIBRARY_LDFLAGS})

这与里面的分号给出了相同的结果:

set_property(TARGET ${PROJECT_NAME} APPEND PROPERTY LINK_FLAGS "${MYLIBRARY_LDFLAGS}")

set_target_properties 在未加引号时扩展为多个字符串，在加引号时扩展为带分号的一个字符串。

我应该如何使用它？

Answer 1

在 CMake 中通过 pkg-config 搜索库的常见工作流程:

# Use pkg-config for search library `xxx`.
pkg_check_modules(XXX xxx)

# Build target which uses given library

# The only command which has no target-oriented equivalent.
# But see comments after the code.
link_directories(${XXX_LIBRARY_DIRS}) 

# Two global commands belows can be replaced by target-oriented equivalent
# after creation of the target.
include_directories(${XXX_INCLUDE_DIRS})
add_compile_options(${XXX_CFLAGS_OTHER})

# Create target
add_executable(my_exe ...) # Or add_library()

# The only target-oriented command, which has no global equivalent.
target_link_libraries(my_exe ${XXX_LDFLAGS_OTHER}) # It is OK to have link flags here
target_link_libraries(my_exe ${XXX_LIBRARIES}) # Can be combined with previous call.

请注意，我们使用 XXX_LDFLAGS_OTHER 变量而不是 XXX_LDFLAGS 变量。这是因为 XXX_LDFLAGS 包括 -l 和 -L 选项，CMake 有更合适的命令。使用 XXX_CFLAGS_OTHER 的类似原因。

---

目前CMake不推荐使用link_directories命令但使用库的绝对路径 target_link_libraries称呼。可以使用 find_library 提取 pkg-config 列出的库的绝对路径命令:

...
# Instead of using `link_directories`, collect absolute paths to libraries.
set(XXX_LIBS_ABSOLUTE)
foreach(lib ${XXX_LIBRARIES})
    # Choose name of variable, which will contain result of `find_library`
    # for specific library.
    set(var_name XXX_${lib}_ABS)
    # Search library under dirs, returned by pkg-config.
    find_library(${var_name} ${lib} ${XXX_LIBRARY_DIR})
    list(APPEND XXX_LIBS_ABSOLUTE ${${var_name}})
endforeach()

# Instead of `target_link_libraries(my_exe ${XXX_LIBRARIES})`
target_link_libraries(my_exe ${XXX_LIBS_ABSOLUTE})