Marshal float/double array at DLLImport of C++ function

[=?ISO-8859-1?Q?Tiago_Falc=E3o?=]

I search on google, msdn,... and i not find no solutions. Any ideia?

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C++ Example Source:

extern "C" __declspec(dllexport)
double * extract(int nrows,int ncols,int * RGB){
int i=0;
int j=ncols*nrows;
double* x;
x=(double*)calloc(1,sizeof(double)); // I
need return one double array
x[0]=((double)RGB[0]+RGB[1]+RGB[2])/3;
return x ;
}

extern "C" __declspec(dllexport)
double distance(double* img1, double* img2){
return img1[0]-img2[0];
}
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C# code:

[DllImport("C:/Users/tiago/Desktop/teste.dll")]
[MarshalAs(UnmanagedType.LPArray, ArraySubType =
UnmanagedType.R8, SizeParamIndex = 1)]
public static extern Double[] extract(int nrows, int ncols,
int[] RGB);

[DllImport("C:/Users/tiago/Desktop/teste.dll")]
public static extern Double distance(Double[] img1, Double[]
img2);

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