Can on marshal a string[] to a safearray variant?

Question

When I marshal my function returning a string[] as UnmanagedType.Struct with SafeArraySubType = VarEnum.VT_ARRAY as in

namespace StackOverflow { [ComVisible(true)] [Guid("4BDC43D4-8FD7-4F58-BEE5-E57C3C144C1B")] public class Array { [return: MarshalAs(UnmanagedType.Struct, SafeArraySubType = VarEnum.VT_ARRAY)] public string[] StringArray() { return new string[] { "foo", "bar" }; } } }

I was expecting to get a variant (UnmanagedType Enumeration)

Struct
A VARIANT, which is used to marshal managed formatted classes and value types.

However the VBScript code

WScript.Echo TypeName(CreateObject("StackOverflow.Array").StringArray)

reports String() (which is not a Variant() and therefore I will get type missmatch errors later when accesing the array).

When I change my code to either

public object[] ObjectArray() { return new object[] { "foo", "bar" }; } public object PlainObject() { return new object[] { "foo", "bar" }; }

the VBScript code seems to works fine, however I would like to know why I cannot return a string[] and manually marshall it to a variant containing a safearray of variants.

It seems that the SafeArraySubType has no effect. What is my mistake?

Alexandre Borela · Accepted Answer · 2015-07-15 15:14:09Z

2

Thats because the SafeArraySubType only applies to SafeArrays.

MarshalAs (UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_VARIANT)]

answered Jul 15, 2015 at 15:14

Alexandre Borela

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2 Comments

Micha Wiedenmann Over a year ago

I find that unlikely given stackoverflow.com/questions/5079200/… uses UnmanagedType.Struct, SafeArraySubType = VarEnum.VT_ARRAY.

Alexandre Borela Over a year ago

That's because the SafeArraySubType is ignored for structs. Structs by the nature are already a "variant array" (msdn.microsoft.com/en-us/library/vstudio/…) because they have their properties layout in sequence.

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