MATLAB: ‘Index exceeds matrix dimensions’ when running a very simple mex function I wrote

mex

I came into 'Index exceeds matrix dimensions' issue when running a very simple mex function I created. This function is called mk_uint32. It shifts the four elements 24,16,8 and 0 bits to the left to create a uint32 number.
Here is the commands I keyed in on the command line:
a=uint32([1 2 3 4]);
b=mk_uint32(a);
and I got the following error message:
Index exceeds matrix dimensions.
Please help me figure out what is wrong. Thanks ahead.
Here is the c code called 'mk_uint32.c'.
#include "mex.h"
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
/* Function Definitions */
uint32_T mk_uint32(uint32_T *indata, uint32_T *outdata)
{
  outdata = (indata[0] << 24U) + (indata[1] << 16U) + (indata[2] << 8U) + indata[3];
}
/* The gateway routine */
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
  uint32_T *x,*y;
    if (nrhs != 1) mexErrMsgTxt("One input required.");
    if (nlhs != 1) mexErrMsgTxt("One output required.");
    /* Create a pointer to the input matrix x. */
    x = mxGetPr(prhs[0]);
    /* Set the output pointer to the output matrix. */
    plhs[0] = mxCreateNumericMatrix(1, 1, mxUINT32_CLASS, mxREAL);
    /* Create a C pointer to a copy of the output matrix. */
    y = mxGetPr(plhs[0]);
    /* Call the C subroutine. */
    mk_uint32(x,y);
  }

Best Answer

In mk_uint32, outdata is a pointer, but you are setting that pointer to a numeric value. You need to store the result in outdata[0] or in *outdata
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