Unable to build mex file - c++

Question

I've followed the MATLAB example for creating a mex file from here https://uk.mathworks.com/help/matlab/matlab_external/standalone-example.html
The source code it produces is as follows
#include "mex.h"
/* The computational routine */
void arrayProduct(double x, double *y, double *z, mwSize n)
{
mwSize i;
/* multiply each element y by x */
for (i=0; i<n; i++) {
z[i] = x * y[i];
}
}
/* The gateway function */
void mexFunction( int nlhs, mxArray *plhs[],
int nrhs, const mxArray *prhs[])
{
double multiplier; /* input scalar */
double *inMatrix; /* 1xN input matrix */
size_t ncols; /* size of matrix */
double *outMatrix; /* output matrix */
/* check for proper number of arguments */
if(nrhs!=2) {
mexErrMsgIdAndTxt("MyToolbox:arrayProduct:nrhs","Two inputs required.");
}
if(nlhs!=1) {
mexErrMsgIdAndTxt("MyToolbox:arrayProduct:nlhs","One output required.");
}
/* make sure the first input argument is scalar */
if( !mxIsDouble(prhs[0]) ||
mxIsComplex(prhs[0]) ||
mxGetNumberOfElements(prhs[0])!=1 ) {
mexErrMsgIdAndTxt("MyToolbox:arrayProduct:notScalar","Input multiplier must be a scalar.");
}
/* make sure the second input argument is type double */
if( !mxIsDouble(prhs[1]) ||
mxIsComplex(prhs[1])) {
mexErrMsgIdAndTxt("MyToolbox:arrayProduct:notDouble","Input matrix must be type double.");
}
/* check that number of rows in second input argument is 1 */
if(mxGetM(prhs[1])!=1) {
mexErrMsgIdAndTxt("MyToolbox:arrayProduct:notRowVector","Input must be a row vector.");
}
/* get the value of the scalar input */
multiplier = mxGetScalar(prhs[0]);
/* create a pointer to the real data in the input matrix */
inMatrix = mxGetPr(prhs[1]);
/* get dimensions of the input matrix */
ncols = mxGetN(prhs[1]);
/* create the output matrix */
plhs[0] = mxCreateDoubleMatrix(1,(mwSize)ncols,mxREAL);
/* get a pointer to the real data in the output matrix */
outMatrix = mxGetPr(plhs[0]);
/* call the computational routine */
arrayProduct(multiplier,inMatrix,outMatrix,(mwSize)ncols);
}
When I run the command mex arrayProduct.cpp (the name of my file), I get the following error:
Building with 'Microsoft Visual C++ 2017'.
Error using mex
LINK : error LNK2001: unresolved external symbol mexfilerequiredapiversion
arrayProduct.lib : fatal error LNK1120: 1 unresolved externals
I'm using MATLAB 2015b 32-bit, with the Visual Studio 2017 C++ compiler. Is there some preliminary set-up required for making mex files that isn't mentioned in the MATLAB tutorial?

Answer 1

The youngest supported compiler for MATLAB R2015b is MSVC Professional 2015. Also, R2015b is the latest version with 32-bit support. Your compiler is probably MSVC 2017, 64-bit.
Try to install .NET4 + SDK 7.1, select that in MATLAB, and re-run your mex command. That is an officially supported compiler for R2015b, and I expect that that solves your problem.
Note: for me, .NET4 refused to install because it detected a previously installed framework, but this answer resolved that problem for me.