All zeros from mex function evaluation
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Hello everyone,
I would like to create one mex function that implements a function defined in a C file.
The C code of the desired function is the following:
/* myFunc */
INTEGER myFunc(type_Md Mode, FLOAT* u1, FLOAT* u2)
{ ...
return status;
}
This function is defined in a C file scr.c with some #include statements which I didn't write.
type_Md is an enumeration type.
To create the mex function I run a Matlab script that includes the needed C files and evaluates the mexFunction:
% Compile myFunc_mex
mexfile = 'myFunc_mex.c';
mexname = 'myFunc_mex';
% Including all files
.....
libfile = 'library.lib';
% Compile in single precision
eval(['mex -Lsrc -l' libfile(1:end-4) ' ' mexfile ' -output ' mexname '_single']);
Based on the definition of myFunc(), I create the C file myFunc_mex.c like this:
#include "mex.h"
#include "math.h"
#include "scr.c"
#include ....
#define MXCLASS mxSINGLE_CLASS
void mexFunction(int nlhs, mxArray *plhs[],
int nrhs, const mxArray *prhs[])
{
type_Md Mode;
INTEGER status;
FLOAT *u1, *u2;
Mode = (type_Md)mxGetScalar(prhs[0]);
plhs[0] = mxCreateNumericMatrix((mwSize)1,1,mxINT16_CLASS,0); /* status */
plhs[1] = mxCreateNumericMatrix((mwSize)1,1,MXCLASS,mxREAL); /* u1 */
plhs[2] = mxCreateNumericMatrix((mwSize)1,1,MXCLASS,mxREAL); /* u2 */
status = (INTEGER)mxGetScalar(plhs[0]);
u1 = (FLOAT *)mxGetPr(plhs[1]);
u2 = (FLOAT *)mxGetPr(plhs[2]);
status = myFunc(Mode, u1, u2);
}
Running the Matlab script I don't get any error, the creation of the mex function is successful. But, evaluating the mex function,
[status,u1,u2] = feval('myFunc_mex_single',Mode1)
I don't get the right result, I get that status, u1 and u2 are ALL ZEROS.
Moreover, if in myFunc_mex.c I substitute the last row with
status = 5;
again I get all zeros. Then I would say that the problem is not (only) in the evaluation of myFunc(), but I'm wrong in defining myFunc_mex.c.
This is the first time I see a mex function, I don't know where the error would be.
采纳的回答
Walter Roberson
2021-8-31
1 个投票
In order to return values, you need to store the values inside the mx arrays that you are creating.
Your u1 and u2 look appropriate to be pointers to the area to write into, but you do not show any code that writes into them.
Your mxGetScalar is reading a value out of the mxINT16_CLASS array that you created. You did not store anything in there, so status is going to be 0 after the mxGetScalar. You then overwrite the local variable status with whatever the function returned, but you never write that status into the memory of that first array -- you would have needed an mxGetPr to get the pointer to it, and then you would have had to store status indirect on that pointer.
3 个评论
Claudia Chiaro
2021-8-31
编辑：Claudia Chiaro
2021-9-1
Walter Roberson
2021-9-2
#include "mex.h"
#include "math.h"
#include "scr.c"
#include ....
#define MXCLASS mxSINGLE_CLASS
void mexFunction(int nlhs, mxArray *plhs[],
int nrhs, const mxArray *prhs[])
{
type_Md Mode;
INTEGER *status_ptr;
FLOAT *u1, *u2;
Mode = (type_Md)mxGetScalar(prhs[0]);
plhs[0] = mxCreateNumericMatrix((mwSize)1,1,mxINT16_CLASS,0); /* status */
plhs[1] = mxCreateNumericMatrix((mwSize)1,1,MXCLASS,mxREAL); /* u1 */
plhs[2] = mxCreateNumericMatrix((mwSize)1,1,MXCLASS,mxREAL); /* u2 */
status_ptr = (INTEGER*)mxGetPtr(plhs[0]);
u1 = (FLOAT *)mxGetPr(plhs[1]);
u2 = (FLOAT *)mxGetPr(plhs[2]);
status_ptr[0] = myFunc(Mode, u1, u2);
}
Claudia Chiaro
2021-9-2
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