PInvoke C function that return pointer

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4.00/5 (1 vote)

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Hi,
I have a C function like this:

C++

double* foo() // function return array of 10 double
{
double* matrix  = (double *)malloc(10 * sizeof(double));
return matrix;
}

how can I write in the wrapper class? Should I do that?

C#

[DllImport("...")]
[return: MarshalAs(UnmanagedType..LPArray)]
public static extern double foo();

Please tell me the way.

Posted 31-May-12 10:11am

Duc Huy Nguyen

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lewax00 · Accepted Answer · 2012-05-31T10:43:00

C#

[DllImport("...")]
public static extern IntPtr foo();

Should work. Then if you know the size of the array:

C#

IntPtr result = foo();
double[] arr = new double[10];
Marshal.Copy(result, arr, 0, 10);

If the array size isn't static, then you should return the size of the array like this:

C++

double* foo(int* size) // function return array of 10 double
{
double* matrix  = (double *)malloc(10 * sizeof(double));
*size = 10;
return matrix;
}

And use:

C#

[DllImport("...")]
public static extern IntPtr foo(out int size);

...

int size;
IntPtr result = foo(out size);
double[] arr = new double[size];
Marshal.Copy(result, arr, 0, size);