C++ error when using MatLab dll: one or more multiply defined symbols found

Question

I am trying to use a MatLab function in C++ by using the MCR (MatLab Compiler Runtime). However, I get an error when I call the function from C++.

This is the output when I try to build:

  1>------ Build started: Project: MatLab DLL Test 2, Configuration: Debug x64 ------

  1>Compiling...

  1>main.cpp

  1>libfoo.cpp

  1>Generating Code...

  1>Linking...

  1>libfoo.lib(libfoo.dll) : error LNK2005: "void __cdecl foo(int,class mwArray &,class mwArray const &)" (?foo@@YAXHAEAVmwArray@@AEBV1@@Z) already defined in libfoo.obj

  1>libfoo.lib(libfoo.dll) : error LNK2005: "void __cdecl foo(int,class mwArray &,class mwArray const &)" (?foo@@YAXHAEAVmwArray@@AEBV1@@Z) already defined in libfoo.obj

  1>C:\Users\fmarsman\Documents\Visual Studio 2008\Projects\Project1\MatLab DLL Test 2\x64\Debug\MatLab DLL Test 2.exe : fatal error LNK1169: one or more multiply defined symbols found

  1>Build log was saved at "file://c:\Users\fmarsman\Documents\Visual Studio 2008\Projects\Project1\MatLab DLL Test 2\MatLab DLL Test 2\x64\Debug\BuildLog.htm"

  1>MatLab DLL Test 2 - 3 error(s), 0 warning(s)

  ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

This is what I have done:

• I created the .m file foo.m:

  function y = foo(x)

  y = x + 1;

• In command prompt, I executed:

  mcc –W cpplib:libfoo –T link:lib foo

• This created libfoo.lib, libfoo.h, libfoo.dll and libfoo.cpp

• Next, I created a project in MS Visual Studio 2008. I added libfoo.cpp to 'Source Files' and libfoo.h to 'Header Files'. I added three directories to Configuration Properties -> C/C++ -> General -> Additional Include Directories:

C:\Users\fmarsman\Documents\MATLAB\DLL Test 2 (the folder where all the libfoo.* files are)

C:\Program Files\MATLAB\MATLAB Compiler Runtime\v82\extern\lib\win64\microsoft (for the mclmcrrt.lib)

C:\MATLAB\R2013b\extern\include (for mclmcrrt.h)

• To Linker -> Input -> Additional Dependencies I added:

"C:\Program Files\MATLAB\MATLAB Compiler Runtime\v82\extern\lib\win64\microsoft\mclmcrrt.lib" "C:\Users\fmarsman\Documents\MATLAB\DLL Test 2\libfoo.lib"

My source code:

  #include <iostream>
  #include <mclmcrrt.h>
  #include <mclcppclass.h>
  #include <libfoo.h>
  using namespace std;

  int main( ) {
    mclInitializeApplication(NULL,0);
    libfooInitialize( );

    mwArray y(1, 1, mxDOUBLE_CLASS);
    y = 3.0;
    const mwArray x = y.Clone();

    foo(1,y,x);

    mclTerminateApplication( );
    libfooTerminate( );

    return 0;
} // main

I've been trying to find a solution all day but without success. I really hope someone can help me with this.

Answer 1

Remove the file libfoo.cpp from your VS studio project. You already import the libfoo.dll, so you're use the function "foo" from the libfoo.dll, so you don't need to include the source into you VS project.