How to use coder.ceval to use mex function in Matlab code and then generate C++ code?

I have Matlab code that I wish to convert to C++. It uses the Matlab-provided example file `mexfunction.c`:

#include "mex.h"
    void
    mexFunction(int nlhs,mxArray *plhs[],int nrhs,const mxArray *prhs[])
    {
        int        i;           
        /* Examine input (right-hand-side) arguments. */
        mexPrintf("\nThere are %d right-hand-side argument(s).", nrhs);
        for (i=0; i<nrhs; i++)  {
            mexPrintf("\n\tInput Arg %i is of type:\t%s ",i,mxGetClassName(prhs[i]));
        }      
        /* Examine output (left-hand-side) arguments. */
        mexPrintf("\n\nThere are %d left-hand-side argument(s).\n", nlhs);
        if (nlhs > nrhs)
          mexErrMsgIdAndTxt( "MATLAB:mexfunction:inputOutputMismatch",
                  "Cannot specify more outputs than inputs.\n");       
        for (i=0; i<nlhs; i++)  {
            plhs[i]=mxCreateDoubleMatrix(1,1,mxREAL);
            *mxGetPr(plhs[i])=(double)mxGetNumberOfElements(prhs[i]);
        }
    }

The Matlab code is below:

function exMexFunction
	B=[0 1; 0 0; 1 0; 1 1];
	C=[1.5 0; 0.5 0; 0.5 1.5; 1.5 1.5];	 
	if coder.target('MATLAB')
	    res=B+C;
	    res1=sum(sum(res));
	    disp(['sum: ',num2str(res1)])
	else	    
	    coder.updateBuildInfo('addSourceFiles','mexfunction.c');
	    P0=0;
	    P0=coder.ceval('mexFunction', B,C);
	end

The resulting error is:

cl /c /Zp8 /GR /W3 /EHs /nologo /MD /D_CRT_SECURE_NO_DEPRECATE /D_SCL_SECURE_NO_DEPRECATE /D_SECURE_SCL=0 /DMATLAB_MEX_FILE /DMATLAB_MEX_FILE /O2 /Oy- /DNDEBUG /fp:strict /I "C:\PROGRA~1\MATLAB\R2018b\simulink\include" /I "C:\PROGRA~1\MATLAB\R2018b\toolbox\shared\simtargets" /I "C:\Users\me\codegen\mex\EXMEXF~1" /I "C:\Users\me" /I ".\interface" /I "C:\PROGRA~1\MATLAB\R2018b\extern\include" /I "." "C:\Users\me/mexfunction.c"
	mexfunction.c
	cl /c /Zp8 /GR /W3 /EHs /nologo /MD /D_CRT_SECURE_NO_DEPRECATE /D_SCL_SECURE_NO_DEPRECATE /D_SECURE_SCL=0 /DMATLAB_MEX_FILE /DMATLAB_MEX_FILE /O2 /Oy- /DNDEBUG /fp:strict /I "C:\PROGRA~1\MATLAB\R2018b\simulink\include" /I "C:\PROGRA~1\MATLAB\R2018b\toolbox\shared\simtargets" /I "C:\Users\me\codegen\mex\EXMEXF~1" /I "C:\Users\me" /I ".\interface" /I "C:\PROGRA~1\MATLAB\R2018b\extern\include" /I "." "exMexFunction_data.c"
	exMexFunction_data.c
	cl /c /Zp8 /GR /W3 /EHs /nologo /MD /D_CRT_SECURE_NO_DEPRECATE /D_SCL_SECURE_NO_DEPRECATE /D_SECURE_SCL=0 /DMATLAB_MEX_FILE /DMATLAB_MEX_FILE /O2 /Oy- /DNDEBUG /fp:strict /I "C:\PROGRA~1\MATLAB\R2018b\simulink\include" /I "C:\PROGRA~1\MATLAB\R2018b\toolbox\shared\simtargets" /I "C:\Users\me\codegen\mex\EXMEXF~1" /I "C:\Users\me" /I ".\interface" /I "C:\PROGRA~1\MATLAB\R2018b\extern\include" /I "." "exMexFunction_initialize.c"
	exMexFunction_initialize.c
	cl /c /Zp8 /GR /W3 /EHs /nologo /MD /D_CRT_SECURE_NO_DEPRECATE /D_SCL_SECURE_NO_DEPRECATE /D_SECURE_SCL=0 /DMATLAB_MEX_FILE /DMATLAB_MEX_FILE /O2 /Oy- /DNDEBUG /fp:strict /I "C:\PROGRA~1\MATLAB\R2018b\simulink\include" /I "C:\PROGRA~1\MATLAB\R2018b\toolbox\shared\simtargets" /I "C:\Users\me\codegen\mex\EXMEXF~1" /I "C:\Users\me" /I ".\interface" /I "C:\PROGRA~1\MATLAB\R2018b\extern\include" /I "." "exMexFunction_terminate.c"
	exMexFunction_terminate.c
	cl /c /Zp8 /GR /W3 /EHs /nologo /MD /D_CRT_SECURE_NO_DEPRECATE /D_SCL_SECURE_NO_DEPRECATE /D_SECURE_SCL=0 /DMATLAB_MEX_FILE /DMATLAB_MEX_FILE /O2 /Oy- /DNDEBUG /fp:strict /I "C:\PROGRA~1\MATLAB\R2018b\simulink\include" /I "C:\PROGRA~1\MATLAB\R2018b\toolbox\shared\simtargets" /I "C:\Users\me\codegen\mex\EXMEXF~1" /I "C:\Users\me" /I ".\interface" /I "C:\PROGRA~1\MATLAB\R2018b\extern\include" /I "." "exMexFunction.c"
	exMexFunction.c
	exMexFunction.c(30): warning C4047: 'function': 'int' differs in levels of indirection from 'real_T [8]'
	exMexFunction.c(30): warning C4024: 'mexFunction': different types for formal and actual parameter 1
	exMexFunction.c(30): warning C4047: 'function': 'mxArray **' differs in levels of indirection from 'real_T [8]'
	exMexFunction.c(30): warning C4024: 'mexFunction': different types for formal and actual parameter 2
	exMexFunction.c(30): error C2198: 'mexFunction': too few arguments for call
	gmake: *** [exMexFunction.obj] Error 2
	??? Build error: C compiler produced errors. See the Build Log for
	further details.
	Code generation failed

What am I doing wrong?