CMake Linking Instructions

Question

I am trying to link a shared object on my executable with an executable in my cmake project.

my CMakeLists.txt

cmake_minimum_required (VERSION 2.8)
project (proto_app)

add_executable( helloDemo hello.cpp )
add_executable( faissDemo 1-Flat.cpp )

My executable faissDemo doesn't compile like this because the shared object is not linked. The shared object is located in /usr/local/lib/libfaiss.so. My question is how should I link to the shared object in CMake?

I can compile 1-Flat.cpp successfully from the command line like: $ g++ 1-Flat.cpp -L /usr/local/lib/ -lfaiss

score 1 · Answer 1 · edited May 02 '19 at 13:54

1

You need to add the dir to the link_directories and add the lib as target_link_libraries:

 cmake_minimum_required (VERSION 2.8)
 project (proto_app)

 link_directories(/usr/local/lib)     

 add_executable( helloDemo hello.cpp )
 add_executable( faissDemo 1-Flat.cpp )
 target_link_libraries(faissDemo faiss)

edited May 02 '19 at 13:54

Kevin

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answered May 02 '19 at 07:18

user6556709

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you mean `link_directories` right? Worked! – mkuse May 02 '19 at 07:22
@mkuse Sorry, yes... – user6556709 May 02 '19 at 07:23
2

Why not just `target_link_libraries(faissDemo /usr/local/lib/libfaiss.so)` – Bernhard May 02 '19 at 07:30
@Bernhard My personal preference is not to use absolute paths in target_link_libraries if it is an installed lib. – user6556709 May 02 '19 at 07:32
2

I have to DV this answer, because `link_directories` is heavily discouraged in CMake, for good reason (it can break dependency tracking, among other things). The preferred alternative is to use absolute paths to libs in `target_link_libraries`. See [note in CMake documentation](https://cmake.org/cmake/help/latest/command/link_directories.html). – Angew is no longer proud of SO May 02 '19 at 07:32
@Angew You would be right if /usr/local/lib would be a private lib path but it isn't. it is a system path. – user6556709 May 02 '19 at 07:34
@user6556709 Even libraries on a system path can change and require re-linking their downstream. – Angew is no longer proud of SO May 02 '19 at 07:39

CMake Linking Instructions

1 Answers1