Avoid automatically added "lib" prefix when using target_link_libraries

Question

I'm trying to link a C++ project to the RCpp library; the file is called Rcpp.so, not the linux-default libRcpp.so. Furthermore, the library resides at the non-standard location /usr/lib/R/site-library/Rcpp/libs.

So I tried using a combination of find_library and target_link_libraries:

cmake_minimum_required(VERSION 3.8)
project("R-Tests")

find_library(RCPP
    NAMES Rcpp.so
    HINTS /usr/lib/R/site-library/Rcpp/libs
)
if (NOT RCPP)
    message(FATAL_ERROR "Could not find Rcpp - exiting.")
else()
    message("Found Rcpp: " ${RCPP})
endif()

# test target
add_executable(rcpptest main.cpp)
target_link_libraries(rcpptest ${RCPP})

Configuring works fine, CMake outputs:

Found Rcpp: /usr/lib/R/site-library/Rcpp/libs/Rcpp.so

However, during build, CMake passes -lRcpp to the compiler, which causes the compilation to fail, since the library file is not named libRcpp.so but instead Rcpp.so:

[100%] Linking CXX executable rcpptest
/usr/bin/cmake -E cmake_link_script CMakeFiles/rcpptest.dir/link.txt --verbose=1
c++     CMakeFiles/rcpptest.dir/main.cpp.o  -o rcpptest  -L/usr/lib/R/site-library/Rcpp/libs -Wl,-rpath,/usr/lib/R/site-library/Rcpp/libs -lRcpp
/usr/bin/ld: cannot find -lRcpp
collect2: error: ld returned 1 exit status

Since the message line prints the full path to the Rcpp.so file just fine, is there any way to let target_link_libraries just add this path to the compiler instead of a combination of -L and -l?

According to this question, this should be disabled by adding cmake_policy(SET CMP0060 NEW); however, I can't see any change in the behavior of CMake if I set this to NEW or OLD.

Maybe you can add the library using [the `LINK_LIBRARIES` property](https://cmake.org/cmake/help/latest/prop_tgt/LINK_LIBRARIES.html) directly on the `rcpptest` target? — Some programmer dude, May 15 '18 at 15:29
Anyway, this must be a common problem, have you tried to search for solutions using your favorite search engine? I doubt there isn't duplicate here on SO. — Some programmer dude, May 15 '18 at 15:31
I searched in the doc, on SO and other sources and haven't found any. — Philipp Ludwig, May 16 '18 at 08:36
Nvm, I found somewhat of a duplicate and edited the question. — Philipp Ludwig, May 16 '18 at 08:48

score 5 · Accepted Answer · answered May 15 '18 at 15:31

5

You may have been bitten by the OLD (default) behavior of CMP0060, which converts absolute paths back to -lfoo.

Alternatively, define and use an IMPORTED target:

add_library(Rcpp SHARED IMPORTED)
set_property(TARGET Rcpp PROPERTY IMPORTED_LOCATION /usr/lib/R/site-library/Rcpp/libs/Rcpp.so)
target_link_libraries(rcpptest Rcpp)

answered May 15 '18 at 15:31

Botje

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Would this also work if lives suddenly in a standard location on a different system? – Philipp Ludwig May 16 '18 at 08:36
Also, ``CMP0060`` doesn't seem to be the issue; I have updated the question to reflect that. – Philipp Ludwig May 16 '18 at 08:49
Good to know. You can combine the `IMPORTED` approach with the path produced by `find_package`. – Botje May 16 '18 at 09:45

Avoid automatically added "lib" prefix when using target_link_libraries

1 Answers1