按照《CMake Practice》中第六章的設定，採用INCLUDE_DIRECTORIES命令去尋找共享庫的路徑，src/CMakeLists.txt如下：

ADD_EXECUTABLE(main main.c)
INCLUDE_DIRECTORIES(/tmp/include/hello)
LINK_DIRECTORIES(/tmp/lib/)
TARGET_LINK_LIBRARIES(main libhello.a)

執行cmake及make後，仍然有link error。

cmake的官網對include_directories的說明如下：

*Specify directories in which the linker will look for libraries.

link_directories(directory1 directory2 …)

Note that this command is rarely necessary. Library locations returned by find_package() and find_library() are absolute paths. Pass these absolute library file paths directly to the target_link_libraries() command. CMake will ensure the linker finds them.*

官網不推薦使用link_directoris，而是推薦使用find_package和find_library尋找共享庫的絕對路徑，再傳給target_link_libraries使用。

按照這裡的例子，改寫了src/CMakeLists.txt如下：

ADD_EXECUTABLE(main main.c)
INCLUDE_DIRECTORIES(/tmp/include/hello)

find_library(LIBHELLO_PATH hello /tmp/lib)
IF(NOT LIBHELLO_PATH)
MESSAGE(FATAL_ERROR "libhello not found"
 
)
ENDIF(NOT LIBHELLO_PATH) 

MESSAGE(STATUS ${LIBHELLO_PATH} " found")
TARGET_LINK_LIBRARIES(main ${LIBHELLO_PATH})

這下可以編譯通過了。