Handling Inputs mex function

Hello, I need help to simply change the inputs "double/string" in the prhs[i] to int/char in mex function. As in the following code

//code works without use prhs[]
#include "mex.h"
#include <string.h>

void mexFunction(int nlhs, mxArray* plhs[], int nrhs,  mxArray* prhs[]) {
    
    char* serialNo = "5584112";
    int N=5;
}

To something like (conversion errors)

//I want to use prhs[]
#include "mex.h"
#include <string.h>

void mexFunction(int nlhs, mxArray* plhs[], int nrhs,  mxArray* prhs[]) {
    
    char* serialNo;
    int N;
    serialNo = prhs[0];
    N = prhs[1];   
}
// Matlab command >> Mymexfunction("5584112",5)
// here "5584112" is a string type and 5 is a double

I tried to converted with type-casting or specific function in mex.h (like "int N = (int)mxGetPr(prhs[1]);") but I don't get what I want. Is it possible to converter like that? what should I do? Thank you

Answer 1

[James Tursa]

The prhs[ ] variables are of type pointer to mxArray ... you cannot use simple native C conversions with them. You must use some API functions for this. E.g., bare bones with no input argument checking:

#include "mex.h"
void mexFunction(int nlhs, mxArray* plhs[], int nrhs, const mxArray* prhs[]) {
    mxArray *mx;
    char* serialNo;
    int N;
    mexCallMATLAB(1,&mx,1,(mxArray **)prhs,"char");
    serialNo = mxArrayToString(mx);
    mxDestroyArray(mx);
    N = (int) mxGetScalar(prhs[1]);
    // insert code here to use serialNo and N
    mxFree(serialNo);
}

Side Note: You could have gotten your attempt at getting the integer to work if you had dereferenced the pointer from mxGetPr first. E.g.,

int N = (int)*mxGetPr(prhs[1]);

But the only way to get your C char string from a MATLAB string type is to use the mexCallMATLAB callback route as I have shown.

[Steven Huynh]

Many thanks!