Call Win32 DLL from .NET with complex struct

Question

I have upgraded an old VB6 component to .NET. This component made a call to another Win32 component, with the following type structure:

Public Type DDPARAMS
    bAddressFlag As String * 1                  
    bCompanyFlag As String * 1                  
    bNameFlag As String * 1                    
    bPremiseFlag As String * 1      
..etc

I cannot reference this Win32 DLL as it is not a COM DLL, so .NET can't create any interop for me automatically.

I have the original source for the Win32 DLL (written in C), and the struct is defined here as:

typedef struct tagDDPARAMS
    {

    BYTE bAddressFlag;             
    BYTE bCompanyFlag;              
    BYTE bNameFlag;                 
    BYTE bPremiseFlag;              

    BYTE sPremiseThreshold[3];    

etc.

When I upgrade the VB6 component, the .NET code generated for the struct is:

Public Structure DDPARAMS Public bAddressFlag() As Char

    <VBFixedString(1), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=1)> Public bCompanyFlag() As Char 

    <VBFixedString(1), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=1)> Public bNameFlag() As Char 

    <VBFixedString(1), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=1)> Public bPremiseFlag() As Char 

    <VBFixedString(3), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=3)> Public sPremiseThreshold() As Char 

    <VBFixedString(3), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=3)> Public sLooseThreshold() As Char

etc.

However, when I run this code, I get the following error:

Type could not be marshaled because the length of an embedded array instance does not match the declared length in the layout.

I have googled and googled and am out of ideas - any help is appreciated.

UPDATE: I tried the suggestion below and changed ByValArray to AnsiBStr (one byte string) and now get the following:

"Cannot marshal field 'sTown' of type 'DDRECORD': Invalid managed/unmanaged type combination (Arrays fields must be paired with ByValArray or SafeArray)."

Thanks a lot Duncan

testalino testalino · Accepted Answer · 2010-09-23T11:15:40

It seems that your declaration is mixed up. Check UnmanagedType, maybe this helps you find the proper types. I would assume that bAddressFlag should be Byte in VB (instead of char) and should be declared with UnmanagedType.U1 for example.

This is just a guess though.

Call Win32 DLL from .NET with complex struct

1 Answers