CMake installs to bin/lib but app can't find lib - linux

Question

I'm building a multi-binary project with cmake and deploying in Debian. CMakeLists.txt reduces down to something like this:
add_library(mylib SHARED lib.cpp) #creates libmylib.so
add_executable(myapp main.cpp)
target_link_libraries(myapp my-lib)
install(TARGETS mylib myapp
RUNTIME DESTINATION bin
LIBRARY DESTINATION lib
)
If I install this to (-DCMAKE_INSTALL_PREFIX=/usr) then I have no problem. But if I install to somewhere else like (-DCMAKE_INSTALL_PREFIX=/opt/myapp, or even -DCMAKE_INSTALL_PREFIX=/usr/local), then I have a problem.
When I run $ /opt/myapp/bin/myapp my application can't find the .so.
I could deploy a script with myapp which sets:
#!/bin/sh
export LD_LIBRARY_PATH=${CMAKE_INSTALL_PREFIX}/lib:$LD_LIBRARY_PATH
exec ${CMAKE_INSTALL_PREFIX}/bin/myapp $*
But this feels like a hack. Plus, the script would need to be generated at configure time with ${CMAKE_INSTALL_PREFIX}/lib.
I imagine that there's a more native way to handle this which lets me simply execute my application from /opt or /usr/local after installation. It would preferably handle this at configure, compile, or install time instead of just before runtime and preferably wouldn't require someone to modify their ~/.bashrc or ~/.profile.
Could you please tell me if there is some way to deploy the standard bin,lib structure in linux to arbitrary paths without the need for pre-runtime scripting?

Answer 1

You should:
use rpath (Unix) or loader_path (MacOS)
or install it in regular system path (/usr/lib or /usr/local/lib etc...)
or use LD_LIBRARY_PATH.
Example to set RPATH:
if(APPLE)
set(CMAKE_INSTALL_RPATH "#loader_path/../lib;#loader_path")
elseif(UNIX)
set(CMAKE_INSTALL_RPATH "$ORIGIN/../lib:$ORIGIN/")
endif()
note: on macos you should now use #rpath
note2: on macos you can use otool -l and otool -L to introspec.
note3: you can use ldd lib.so and objdump -p lib.so on GNU/Linux.
Note: Prefer to use GNUInstallDirs
include(GNUInstallDirs)
install(TARGETS ${PROJECT_NAME}
INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)