Calling a DLL generated by MatLab from VC

Matlab version is 2009b, and VC version is 2008，the program is calling a DLL generated by the Matlab function normrnd.m to obtain 100 random numbers.

 mxArray *norm_out; 
 mxArray *norm_in[4]; 
 double r[100]; 
 int main() 
 { 
 if ( !mclInitializeApplication(NULL,0) ) 
     { 
         fprintf(stderr, "Could not initialize the application.\n" ); 
         printf("Hello\n"); 
         exit(1); 
     } 
 if (!libpkgInitialize()) 
     { 
         fprintf(stderr, "Could not initialize the library.\n" ); 
         exit(1); 
     } 

 norm_in[0] = mxCreateScalarDouble(0.0); 
 norm_in[1] = mxCreateScalarDouble(1.0); 
 norm_in[2] = mxCreateScalarDouble(1); 
 norm_in[3] = mxCreateScalarDouble(100); 

 norm_out = mxCreateDoubleMatrix(1,100,mxREAL); 
 mlxNormrnd(1,norm_out,4,norm_in); 
 memcpy(r,norm_out,100*sizeof(double))；

However, the outputs of array r are all zeros. What's the problem?

Answer 1

[Titus Edelhofer]

Hi,

it's the last memcpy that's wrong: you should not use the datastructure norm_out, but the data of norm_out, i.e.,

memcpy(r,mxGetPr(norm_out),100*sizeof(double))；

Alternative: at the top write

double *r = null;

and instead of a memcpy just do

r = mxGetPr(norm_out);

Titus

EDIT: changed mxGetPr call.

[iar]

I'm using C not C++ to call the DLL, I try it but cannot solve the problem, can you tell me more details, and what's the differences between the two methods?

Thanks.

[Titus Edelhofer]

Hi Iar,

my fault: I've been programming too much in object oriented languages the last days ... I changed the call to mxGetPr to be correct C syntax now.

Thanks, Titus

[iar]

I think that's no difference between double *r and double r[100],and I modify the code in your way, but the problem is still there, could you practice it and tell me your result?

Thanks.

[Titus Edelhofer]

Hi,

of course, the declaration of r as double* or double r[100] is the same.

Nnow I see another mistake: don't initialize norm_out, i.e., replace the line

norm_out = mxCreateDoubleMatrix(...);

by

norm_out = null;

Titus

[iar]

The problem is solved when I modify the function: mlxNormrnd(1,norm_out,4,norm_in); into mlxNormrnd(1,&norm_out,4,norm_in);

Thanks for your attention.