Wrong read in mex function

Hi, in main.m i create numeri (vector of int).

In mex file i have:

int *numeri;

void mexFunction(int nlhs , mxArray *plhs[] , int nrhs , const mxArray *prhs[]) {

 // Parse "numeri"

    if ( mxGetNumberOfDimensions( prhs[2] ) != 2 || mxGetN(prhs[2]) != 1 )

                mexErrMsgIdAndTxt("InvalidInput:numeri","'numeri' must be a column vector");

    numeri = (int*) mxGetData(prhs[2]);

for(int i=0;i<10;i++)

printf("%d \n",numeri[i]);

}

the printed values are not the same that I get in the main. Why?

Thanks,

Davide

Answer 1

[Geoff Hayes]

Davide - how are you calling this function? And in particular, what are the inputs? I suspect that there might be a problem with the third input to this function.

I took your code and placed it in a function called testfunc.c and then ran mex testfunc.c. In the Command Window, I typed the following two lines

 v = [1:10]';
 testfunc(2,3,v)

and the output from the printfs in the C code was

 0 
 1072693248 
 0 
 1073741824 
 0 
 1074266112 
 0 
 1074790400 
 0 
 1075052544

So not the 1,2,3,...,10. This "error" actually makes sense. In the Command Window, check the data type of the vector v

 class(v)

 ans =
    double

So we are passing in an array of doubles, but the C-code is expecting an array of integers

 int *numeri;

and later

 numeri = (int*) mxGetData(prhs[2]);

So we have to change the data type of the input data from double to int32. We can do this as

 v = int32([1:10]');
 testfunc(2,3,v)

and the output this time is

 1 
 2 
 3 
 4 
 5 
 6 
 7 
 8 
 9 
 10

Hope that this helps!