Question

I have a legacy VB6 application that has the following structure defined:

Public Type DrawDown
    Date As Date
    Amount As Currency
    CapitaliseInterest As Boolean
End Type

An interop assembly is generated using tlbimp.exe but the structure ends up as the following:

[StructLayout(LayoutKind.Sequential, Pack = 4)]
public struct DrawDown
{
    public DateTime Date;
    [MarshalAs(UnmanagedType.Currency)]
    public decimal Amount;
    public short CapitaliseInterest;
}

I’m using .NET 4.0.

Why does the VB6 Boolean get translated to a C# short instead of a bool?

Answer 1

VB6 uses the VARIANT_BOOL type,

find info and history about it here: BOOL vs. VARIANT_BOOL vs. BOOLEAN vs. boo

Off to the side came VARIANT_BOOL.

typedef short VARIANT_BOOL; define VARIANT_TRUE ((VARIANT_BOOL)-1)
define VARIANT_FALSE ((VARIANT_BOOL)0) This was developed by the
Visual Basic folks. Basic uses -1 to represent “true” and 0 to
represent “false”, and VARIANT_BOOL was designed to preserve this
behavior.