cmake compile issue

[yanboyang713]

Hello All,

Good day to you.

Currently, I am try to using cmake download and build the libqxx.
But, it is show libns3.37-database-default.so: undefined reference to `pqxx::internal::check_pqxx_version_7_6()
anyone know the reason why? Thanks for your help.

cmake:

include(FetchContent)

cmake_minimum_required (VERSION 3.10)
project(example VERSION 1.0.0 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

FetchContent_Declare(
  libpqxx
  GIT_REPOSITORY https://github.com/jtv/libpqxx.git
  #GIT_TAG 3d97c80bcde96fb70a21c1ae1cf92ad934818210
  GIT_TAG 90768b07f7feb55a9bd70cfaacb5543bfd074022
)
set(PQXX_LIBRARIES pqxx)

FetchContent_MakeAvailable(libpqxx)

set(source_files
    model/database.cc
)

set(header_files
    model/database.h
)
build_lib(
  #add_link_options(-lpqxx -lpq)

  LIBNAME database
  SOURCE_FILES ${source_files}
  HEADER_FILES ${header_files}
  LIBRARIES_TO_LINK ${PQXX_LIBRARIES}
  #LIBRARIES_TO_LINK pqxx pq
)

ERROR MSG:

/usr/bin/ld: /home/yanboyang713/projects/test/ns3-learning/ns-allinone-3.37/ns-3.37/build/lib/libns3.37-database-default.so: undefined reference to `pqxx::internal::check_pqxx_version_7_6()'
collect2: error: ld returned 1 exit status
make[3]: *** [scratch/CMakeFiles/scratch_anomalyPrediction_anomalyPrediction.dir/build.make:116: /home/yanboyang713/projects/test/ns3-learning/ns-allinone-3.37/ns-3.37/build/scratch/anomalyPrediction/ns3.37-anomalyPrediction-default] Error 1
make[2]: *** [CMakeFiles/Makefile2:5248: scratch/CMakeFiles/scratch_anomalyPrediction_anomalyPrediction.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:5254: scratch/CMakeFiles/scratch_anomalyPrediction_anomalyPrediction.dir/rule] Error 2
make: *** [Makefile:2101: scratch_anomalyPrediction_anomalyPrediction] Error 2

[tt4g]

Commit SHA 90768b0 is included in version 7.7.3.
As far as the symbol name pqxx::internal::check_pqxx_version_7_6() is concerned, libns3.37-database-default.so expects libpqxx version 7.6.
The header file referenced when building the ns library is wrong.

[jtv]

Exactly. It looks like libns was built with libpqxx 7.6, but the installed libpqxx is a different version.

This is a general problem with rich ABIs like you get in C++, and so I generally recommend using libpqxx as a static library rather than as a shared library.

[yanboyang713]

Hello Jeroen, Thanks for your help. I think the problem comes from the line " LIBRARIES_TO_LINK ${PQXX_LIBRARIES}." I guess NS3 LIBRARIES_TO_LINK macro link as a shared library by default. Do you know how to link as a static library? Have a nice day, Boyang Yan

…

Message ID: ***@***.***>

[tt4g]

libpqxx is a static library unless the BUILD_SHARED_LIBS variable is defined with a value that evaluates to truthy: https://cmake.org/cmake/help/v3.26/variable/BUILD_SHARED_LIBS.html

libpqxx/src/CMakeLists.txt

Line 69 in 3d97c80

add_library(pqxx ${CXX_SOURCES})

Set BUILD_SHARED_LIBS to FALSE once before FetchContent_MakeAvailable() because FetchContent_MakeAvailable() calls FetchContent_Populate() and add_subdirectory().
See: https://cmake.org/cmake/help/v3.26/module/FetchContent.html

+set(BUILD_SHARED_LIBS_TMP ${BUILD_SHARED_LIBS})
+set(BUILD_SHARED_LIBS FALSE)
 FetchContent_MakeAvailable(libpqxx)
+set(BUILD_SHARED_LIBS ${BUILD_SHARED_LIBS_TMP})

And since there is no build_lib function in CMake functions, it is not clear to us what it is doing.
When linking libraries in CMake, we usually use target_link_libraries().
If you use the other way, CMake will not propagate library information that must be linked when using the pqxx target, and macros that must be defined at build time.

+add_library(${your_library_name} ${source_files ...})
+target_link_libraries(${your_library_name} PRIVATE pqxx)
-build_lib(
-  #add_link_options(-lpqxx -lpq)
-
-  LIBNAME database
-  SOURCE_FILES ${source_files}
-  HEADER_FILES ${header_files}
-  LIBRARIES_TO_LINK ${PQXX_LIBRARIES}
-  #LIBRARIES_TO_LINK pqxx pq
-)

[jtv]

Looks like we're done with this ticket. Thanks once again @tt4g for jumping in so quickly.