I have installed rdkafka locally on my machine via the apt package manager as instructed in their documentation. Now I want to link to that library with CMake so I can use it.
I am currently trying it like this:
find_package(PkgConfig REQUIRED) pkg_check_modules(rdkafka REQUIRED rdkafka) target_include_directories(myTarget PUBLIC ${RDKAFKA_INCLUDE_DIRS}) target_link_libraries(myTarget PUBLIC ${RDKAFKA_LDFLAGS}) It finds the rdkafka library but when trying to build the target it still has undefined references. It does work with the glib library though.
EDIT: This is the output when configuring CMake:
-- Checking for module 'rdkafka' -- Found rdkafka, version 1.8.0 -- Configuring done -- Generating done -- Build files have been written to: Starting the build leads to this:
/usr/bin/ld: CMakeFiles/ in function `g_autoptr_cleanup_generic_gfree': opc_kafka_bridge.c:(.text+0x6c6): undefined reference to `g_free' /usr/bin/ld: CMakeFiles/ in function `glib_autoptr_clear_GError': opc_kafka_bridge.c:(.text+0x6e8): undefined reference to `g_error_free' /usr/bin/ld: CMakeFiles/ in function `glib_autoptr_clear_GKeyFile': opc_kafka_bridge.c:(.text+0x726): undefined reference to `g_key_file_unref' /usr/bin/ld: CMakeFiles/ in function `load_config_group': opc_kafka_bridge.c:(.text+0x7a8): undefined reference to `g_key_file_get_keys' /usr/bin/ld: opc_kafka_bridge.c:(.text+0x7eb): undefined reference to `g_log' /usr/bin/ld: opc_kafka_bridge.c:(.text+0x822): undefined reference to `g_key_file_get_string' /usr/bin/ld: opc_kafka_bridge.c:(.text+0x861): undefined reference to `g_log' /usr/bin/ld: opc_kafka_bridge.c:(.text+0x8b9): undefined reference to `g_log' /usr/bin/ld: CMakeFiles/ in function `dr_msg_cb': opc_kafka_bridge.c:(.text+0x95b): undefined reference to `g_log' /usr/bin/ld: CMakeFiles/ in function `sendKafkaMessage': opc_kafka_bridge.c:(.text+0x9a4): undefined reference to `g_key_file_new' /usr/bin/ld: opc_kafka_bridge.c:(.text+0x9d0): undefined reference to `g_key_file_load_from_file' /usr/bin/ld: opc_kafka_bridge.c:(.text+0xa00): undefined reference to `g_log' /usr/bin/ld: opc_kafka_bridge.c:(.text+0xaa0): undefined reference to `g_log' /usr/bin/ld: opc_kafka_bridge.c:(.text+0xbc5): undefined reference to `g_log' /usr/bin/ld: opc_kafka_bridge.c:(.text+0xc03): undefined reference to `g_log' /usr/bin/ld: opc_kafka_bridge.c:(.text+0xc4e): undefined reference to `g_log' /usr/bin/ld: CMakeFiles/(.text+0xca4): more undefined references to `g_log' follow collect2: error: ld returned 1 exit status gmake[2]: *** [CMakeFiles/ OPCKafkaBridge] Error 1 gmake[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/ Error 2 gmake: *** [Makefile:91: all] Error 2 I managed to get it to compile by creating a Makefile manually with the following contents:
CFLAGS=-Wall $(shell pkg-config --cflags glib-2.0 rdkafka) LDLIBS=$(shell pkg-config --libs glib-2.0 rdkafka) I hope someone can help me configure should there be a mistake with the way I am trying to link to the library or point me in the right direction if it's correct and the problem is something different.
41 Answer
librdkafka provides a CMake config file and pkg-config files, so you have 2 solutions:
find_package(RdKafka REQUIRED) target_link_libraries(myTarget PUBLIC RdKafka::rdkafka) or
find_package(PkgConfig REQUIRED) pkg_check_modules(rdkafka REQUIRED IMPORTED_TARGET rdkafka) target_link_libraries(myTarget PUBLIC PkgConfig::rdkafka) if you want to link rdkafka++:
find_package(RdKafka REQUIRED) target_link_libraries(myTarget PUBLIC RdKafka::rdkafka++) or
find_package(PkgConfig REQUIRED) pkg_check_modules(rdkafka++ REQUIRED IMPORTED_TARGET rdkafka++) target_link_libraries(myTarget PUBLIC PkgConfig::rdkafka++) 
