PInvoke - How to convert IntPtr to double[]?

[senglory]

        [DllImport("PlainCLibrary.dll")]
        internal static extern IntPtr TestDoubleArray(double[] dbl, long len);

The underlying TestDoubleArray() returns double*. I'd like to have it converti=ed on my C# side to double[]. How can I do it?

[Mutant_Fruit]

How do you know how long the array is? If you know exactly how long it is, you can just instantiate a double[] of the correct size and then use Marshal.Copy. If you don't know how long it is, there's nothing you can do.

[senglory]

If, for example, I know the size of returned data, is it possible to avoid Marshal.Copy()?

[Mutant_Fruit]

Nope, probably not. Does the function require you to free the returned pointer or does the native library 'own' the pointer? Also, is the size of the double* constant? i.e. is it *always* going to be a fixed size like 6 elements?

[thomus07]

If, for example, I know the size of returned data, is it possible to avoid Marshal.Copy()?

In unsafe block.

[Mutant_Fruit]

Which is no better than what Marshal.Copy does except now you've made your library unsafe. You're better off just using Marshal.Copy.

[thomus07]

Which is no better than what Marshal.Copy does except now you've made your library unsafe. You're better off just using Marshal.Copy.

I agree, but he can prevent the copy.

[Mutant_Fruit]

I agree, but he can prevent the copy.

If he wants a managed double [] then there's no way for him to prevent the copy. No matter how it's achieved, a new double[] of the required length will be created and the data will be copied from the double* to the double[]. If he wants to pass a double * around the place and use that directly, then sure, he can prevent the copy. However he'd also open himself up to a whole bunch of memory corruption issues which couldn't happen if he just marshalled the double* straight away. There's absolutely no reason to avoid Marshal.Copy if you want a managed double[].