Building a MATLAB mex file in Visual Studio gives “LNK2019 unresolved external symbol _mexPrintf referenced in function mexFunction”?

Question

I'm using Visual Studio 2012 x64 to build and debug a MATLAB 2014a x64 mex file directly (without using the mex command in MATLAB). I followed the instructions in this question to set up a Visual Studio project named test1. I followed this tutorial to write a simple mex file, test1.cpp:

#include <math.h>
#include <matrix.h>
#include <mex.h>

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
  mexPrintf("Hello World!\n");
}

Building this solution gives me this message:

> 1>------ Build started: Project: test1, Configuration: Debug Win32
> ------ 1>     Creating library C:\PROJECTS\matlab\mex\test1\Debug\test1.lib
> and object
> C:\PROJECTS\matlab\mex\test1\Debug\test1.exp
> 1>test1.obj : error LNK2019: unresolved external symbol _mexPrintf
> referenced in function _mexFunction 1>MSVCRTD.lib(crtexe.obj) : error
> LNK2019: unresolved external symbol _main referenced in function
> ___tmainCRTStartup 1>C:\PROJECTS\matlab\mex\test1\Debug\test1.mexw64
> : fatal error LNK1120: 2 unresolved externals
> ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Are there configuration steps I'm missing here? I used the steps in this answer exactly, but maybe it's incomplete for more recent versions of MATLAB?

Answer 1

You need to create a Visual Studio project that produces DLLs (as opposed to console or GUI applications). MEX-files are basically shared libraries with a custom extension (*.mexw32 or *.mexw64 on Windows)

The error message indicates that the linker cannot find the entry-point function main() for an executable, which does not exist for dynamic libraries.

For what it's worth, you can run mex -v ... in MATLAB, that way it shows you the exact commands used to invoke the compiler and linker.

---

EDIT:

Step-by-step instructions:

• create a new empty VS project to build DLLs (Visual C++ > Win32 > Win32 console application then set the type to DLL in the wizard)

• Since we're working with MATLAB x64, we need to adjust project configuration to generate 64-bit binaries. From Build menu, select Configuration Manager. From the drop-down menu choose <New> to create a new platform configs, select x64 and accept.

• follow the previous instructions you mentioned

• add the C/C++ source code for the MEX-file

  #include "mex.h"
  void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
  {
      plhs[0] = mxCreateString("hello world");
  }
  

• switch platform to "x64" in "Release" mode, and build the project. Now you should have a somefile.mexw64 MEX-file which you can call in MATLAB as a regular function.