[Dune] Link to external shared library

[Tobias Kasper Skovborg Ritschel]

That did the trick. Thanks a lot for the help, especially since it turned out not to be Dune related.

-----Original Message-----
From: Jö Fahlke [mailto:jorrit at jorrit.de] 
Sent: 18. maj 2017 10:02
To: Tobias Kasper Skovborg Ritschel
Cc: dune at dune-project.org
Subject: Re: [Dune] Link to external shared library

Am Thu, 18. May 2017, 06:55:03 +0000 schrieb Tobias Kasper Skovborg Ritschel:
> Date: Thu, 18 May 2017 06:55:03 +0000
> From: Tobias Kasper Skovborg Ritschel <tobk at dtu.dk>
> To: "dune at dune-project.org" <dune at dune-project.org>
> Subject: Re: [Dune] Link to external shared library
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> I don't know of any advantages in using add_library and set_target_properties. I had found both approaches. I've changed it to use include_directories and target_link_libraries:
> 
>  
> ----------------------------------------------------------------------
> ---------------------------------------------------------------------
> 
> # Find the ThermoLib library
> find_library(thermolib_LIBRARY ThermoLib) message(STATUS "setting 
> thermolib_LIBRARY="${thermolib_LIBRARY}"")
> 
> # Find the ThermoLib include directory 
> find_path(thermolib_INCLUDE_DIRS ThermoLib.h) message(STATUS "setting 
> thermolib_INCLUDE_DIRS="${thermolib_INCLUDE_DIRS}"")
> 
> # Add executable
> add_executable("ResSim"	main.cc)
> 
> # Include directories
> include_directories("${thermolib_INCLUDE_DIRS}")
> 
> # Link libraries
> target_link_dune_default_libraries("ResSim")
> target_link_libraries("ResSim" "${thermolib_LIBRARY}")
> 
>  
> ----------------------------------------------------------------------
> ---------------------------------------------------------------------
> 
> The problem remains. "make VERBOSE=1" returns
> 
> cd /home/tobk/Documents/Projects/ResSim/release/src && /usr/bin/cmake -E cmake_link_script CMakeFiles/ResSim.dir/link.txt --verbose=1
> /usr/bin/g++   -Wall -std=c++14  -O3 -DNDEBUG   -Wl,-no-as-needed -pthread  -Wl,-no-as-needed -pthread CMakeFiles/ResSim.dir/main.cc.o  -o ResSim  -L/home/tobk/Documents/Projects/ThermoLib/lib -rdynamic /usr/local/lib/libdunegrid.a /usr/local/lib/libdunegeometry.a /usr/local/lib/libdunecommon.a -lldl -lspqr -lumfpack -lcholmod -lamd -lcamd -lcolamd -lccolamd -lsuitesparseconfig -lsuperlu -lblas -llapack -lblas -pthread /usr/lib/openmpi/lib/libmpi.so /usr/local/lib/libdunegrid.a /usr/local/lib/libdunegeometry.a /usr/local/lib/libdunecommon.a -lThermoLib -llapack -lblas -Wl,-rpath,/usr/lib/openmpi/lib:/home/tobk/Documents/Projects/ThermoLib/lib 
> CMakeFiles/ResSim.dir/main.cc.o: In function `main':
> main.cc:(.text.startup+0x87): undefined reference to `LoadParams(int*, int, int, double*, double*)'
> collect2: error: ld returned 1 exit status
> 
> I can't detect the problem with the above. It has "-L/home/tobk/Documents/Projects/ThermoLib/lib" and "-lThermoLib".

The linker also found libThermoLib.so, otherwise it would have complained about missing that before complaining about undefined references.

I can offer the following lead:

- Is the linkage of LoadParams correct?
  If ThermoLib is a C library, LoadParams will be put in the lib using C
  linkage.  If you include the thermolib header from a C++ program, all
  function declarations will declare functions in C++ linkage (i.e. with name
  mangling) by default.  Try
  ```
  extern C {
  #include <TermoLib.h>
  }
  ```
  instead of just a plain include.  Really, TermoLib.h should probably wrap
  all its declarations when it detects a C++ compiler, i.e. from openmpi's
  [mpi.h](https://github.com/open-mpi/ompi/blob/master/ompi/include/mpi.h.in#L318):
  ```
  //...
  #if defined(c_plusplus) || defined(__cplusplus)
  extern "C" {
  #endif
  // declarations here
  #if defined(c_plusplus) || defined(__cplusplus)
  }
  #endif
  //...
  ```

Regards, Jö.

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