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• ISSUE #1050

TODO #1050

Structure %1 may require marshalling attributes to be passed as an argument in this Declare statement.

Description

In Visual Basic 6.0, user-defined types could be passed as an argument in a Declare statement for a Windows API.

In Visual Basic .NET, a structure (user-defined type) passed as an argument in a Declare statement may require additional marshalling attributes in order to be passed correctly to the external function or subroutine. In particular, arrays and fixed-length strings may not function as expected without these attributes.

Recommendations

Add an Imports statement to reference the System.Runtime.InteropServices namespace and then modify the structure and the string declaration to include marshalling attributes. 

Sample VB6

Private Type MyStructure
   Name AsString
   Size AsInteger
End Type

DeclareFunction FunctionName Lib"MyLibrary.DLL" (ByVal rs1 As MyStructure) AsLong

Target VB.NET

PrivateStructure MyStructure
      Dim Name AsString
      Dim Size AsInteger
      PublicSharedFunction CreateInstance() As MyStructure
           Dim result AsNew MyStructure
           result.Name = String.Empty
           Return result
     EndFunction
EndStructure

'UPGRADE_WARNING: (1050) Structure MyStructure may require marshalling attributes to be passed as an argument in this Declare statement.
DeclareFunction FunctionName Lib"MyLibrary.DLL" (ByVal rs1 As MyStructure) AsInteger

Expected VB.NET

PrivateStructure MyStructure
       <MarshalAs(UnmanagedType.ByValTStr)> Dim Name AsString
       <MarshalAs(UnmanagedType.I4)> Dim Size AsInteger
       PublicSharedFunction CreateInstance() As MyStructure
             Dim result AsNew MyStructure
             result.Name = String.Empty
             Return result
      EndFunction
EndStructure

DeclareFunction FunctionName Lib"MyLibrary.DLL" (ByVal rs1 As MyStructure) AsInteger

Target C#

publicstructMyStructure
{
     publicstring Name;
     publicint Size;

     publicstaticMyStructure CreateInstance()
     {
           MyStructure result = newMyStructure();
           result.Name = String.Empty;
           return result;
     }
}
//UPGRADE_WARNING: (1050) Structure MyStructure may require marshalling attributes to be passed as an argument in this Declare statement.
[DllImport("MyLibrary.DLL")]
publicexternstaticint FunctionName( MyStructure rs1);

Expected C#

publicstructMyStructure
{
     [MarshalAs(UnmanagedType. ByValTStr)]
     publicstring Name;
     [MarshalAs(UnmanagedType.I4)]
     publicint Size;

    publicstaticMyStructure CreateInstance()
    {

               MyStructure result = newMyStructure();
               result.Name = String.Empty;
               return result;
    }
}

 [DllImport("MyLibrary.DLL")]
 publicexternstaticint FunctionName( MyStructure rs1);

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