How can a MEX file give parameters to a C++ program?

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Mana V
Mana V 2015-8-5
编辑： James Tursa 2015-8-5
Hello!
I am coding a program in MATLAB, in which I have to call a C++ library. To do so, I created a C++ file that calls the library and then a MEX-file that help me to call the desired function in MATLAB. The function I want to access in the library returns me a value, but I have to give it parameters. I am currently able to retrieve a value, because I write my parameteres directly in the C++ code as you can see here (my file's name is Test704()):
// Test704.cpp : Defines the entry point for the console application.
#define _AFXDLL
#include "StdAfx.h"
#include "704IO.h"
#include "Test704.h"
#include "mex.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#endif
/////////////////////////////////////////////////////////////////////////////
CWinApp theApp; // The one and only application object
/////////////////////////////////////////////////////////////////////////////
using namespace std;
/////////////////////////////////////////////////////////////////////////////
//int _tmain(int argc, TCHAR *argv[], TCHAR *envp[])
int _tmain(double port[], double rack[], double offset[])
{
double valueRead;
//short port;
//short rack;
//short offset;
// valueRead = PortRead(1, 780, -1);
valueRead = PortRead(port[0], rack[0], offset[0]);
mexPrintf("Value Read = %i\n",valueRead);
return valueRead;
}
/////////////////////////////////////////////////////////////////////////////
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
double *port, *rack, *offset;
// Creates a 1-by-1 real integer.
//plhs[0] = mxCreateNumericMatrix(1, 1, mxINT32_CLASS, mxREAL);
plhs[0] = mxCreateNumericMatrix(1, 1, mxINT32_CLASS, mxREAL);
int* data = (int*) mxGetData(plhs[0]);
port = mxGetPr(prhs[0]);
rack = mxGetPr(prhs[0]);
offset = mxGetPr(prhs[0]);
//valueRead = mxGetPr(plhs[0]);
//data[0]=_tmain(0,0,0);
//return ;
data[0] = _tmain(port,rack,offset);
return ;
}
You will notice that I have commented parts of the code in order to make researches. Indeed, I want now to be able to give parameters by this way (MATLAB code):
x = 1;
y = 780;
z = 1;
myVal = double(Test704(x,y,z));
and to still be able to retrieve a value in myVal. I helped myself with the example timestwo.c provided by MathWorks, but unfortunately, it just returns me a value of 0 instead of 2 or 4, and I cannot figure out why.
Thanks for help,
Mana

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采纳的回答

James Tursa
James Tursa 2015-8-5
编辑：James Tursa 2015-8-5
In this line you are using an integer output format %i to print a floating point double value:
mexPrintf("Value Read = %i\n",valueRead);
That will not work. You need to use one of the floating point formats for this. E.g.,
mexPrintf("Value Read = %g\n",valueRead); // or %f or %e
Once that is fixed you will get the proper value printed to the screen and see if it is correct at that point in the code. Also, I find it a bit strange that you are using a double for valueRead even though the function _tmain returns an int.
Then there are typos in your inputs. The following lines of code get the pointers from the 1st argument, not the 1st three arguments:
port = mxGetPr(prhs[0]);
rack = mxGetPr(prhs[0]);
offset = mxGetPr(prhs[0]);
So change that to:
port = mxGetPr(prhs[0]);
rack = mxGetPr(prhs[1]);
offset = mxGetPr(prhs[2]);
And if you want the output to be a double at your m-file level, why not just return a double variable from the mex routine? E.g.,
plhs[0] = mxCreateDoubleScalar( _tmain(port,rack,offset) );

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