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From: Feixiong on 19 Jan 2010 08:44
Hello,
I am now using gateway functions to call c function to speedup the program and encounterimh some problem. I am a new to matlan and c. hope you can help me!

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]){
....
long int *arg_val;
arg_va = (long int *) mxGetPr(prhs[0]);
.....
}

i am wondering after the type change why the content is set to be zero.

Thanks
From: James Tursa on 19 Jan 2010 09:43
"Feixiong " <f.liao(a)tue.nl> wrote in message <hj4cv4$nfh$1(a)fred.mathworks.com>...
> Hello,
> I am now using gateway functions to call c function to speedup the program and encounterimh some problem. I am a new to matlan and c. hope you can help me!
>
> void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]){
> ...
> long int *arg_val;
> arg_va = (long int *) mxGetPr(prhs[0]);
> ....
> }
>
> i am wondering after the type change why the content is set to be zero.
>
> Thanks

mxGetPr returns a double *. Changing this to a long int * doesn't look right. What is the type of variable that you are calling the mex function with? int32? Or what? Usually one would do this instead:

int *arg_val;
arg_va = (int *) mxGetData(prhs[0]);

But the above works only if the int is a 32-bit integer and prhs[0] is a class int32 variable. If you are actually trying to convert a double input into an int in the C code, you would do this:

int arg_val;
arg_va = *mxGetPr(prhs[0]);

You need to clarify what you are actually intending to do.

James Tursa
From: Feixiong on 19 Jan 2010 10:00

> mxGetPr returns a double *. Changing this to a long int * doesn't look right. What is the type of variable that you are calling the mex function with? int32? Or what? Usually one would do this instead:
>
> int *arg_val;
> arg_va = (int *) mxGetData(prhs[0]);
>
> But the above works only if the int is a 32-bit integer and prhs[0] is a class int32 variable. If you are actually trying to convert a double input into an int in the C code, you would do this:
>
> int arg_val;
> arg_va = *mxGetPr(prhs[0]);
>
> You need to clarify what you are actually intending to do.
>
> James Tursa

hi James,

what i am intending to do is:
prhs[0]) contains a n-length of 1-D array of integer numbers, which is the index of another 2-D array input prhs[1]).

But after mxGetdata or mxGetpr, prhs[0]) was changed to double, which is can't be used as index directly.

Thanks, is there any solution for this?
From: Stefan on 19 Jan 2010 10:05
How about this:

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]){
long int *arg_val;
double *arg_ret;

// computation
....

arg_ret = mxGetPr(prhs[0]);
*arg_ret = (double) *arg_val;

}

Regards,
Stefan
From: Stefan on 19 Jan 2010 10:10

Ah, right hand side ...

to use it for indexing you need to dereference somewhere. There you can cast it to integer.
Or simply make a copy with the appropriate type.

Regards,
Stefan


"Feixiong " <f.liao(a)tue.nl> wrote in message <hj4he6$fra$1(a)fred.mathworks.com>...
>
> > mxGetPr returns a double *. Changing this to a long int * doesn't look right. What is the type of variable that you are calling the mex function with? int32? Or what? Usually one would do this instead:
> >
> > int *arg_val;
> > arg_va = (int *) mxGetData(prhs[0]);
> >
> > But the above works only if the int is a 32-bit integer and prhs[0] is a class int32 variable. If you are actually trying to convert a double input into an int in the C code, you would do this:
> >
> > int arg_val;
> > arg_va = *mxGetPr(prhs[0]);
> >
> > You need to clarify what you are actually intending to do.
> >
> > James Tursa
>
> hi James,
>
> what i am intending to do is:
> prhs[0]) contains a n-length of 1-D array of integer numbers, which is the index of another 2-D array input prhs[1]).
>
> But after mxGetdata or mxGetpr, prhs[0]) was changed to double, which is can't be used as index directly.
>
> Thanks, is there any solution for this?
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