Passing Array of string from C# application to C++ DLL

Question

string []URL = {"www.facebook.com","www.orkut.com","www.yahoo.com"};
            Int32 result = URL.Length;
            SetPolicyURL( URL,result );

this is my C# code where i am trying to pass the array of string to C++ Dll which is imported like this

     [PreserveSig]
    [DllImport("PawCtrl.dll", SetLastError = true, CharSet = CharSet.Auto,  CallingConvention = CallingConvention.StdCall)]
    public static extern void SetPolicyURL( string []policy, Int32 noURL);

but i am not able to receive it in my c++ DLL .

 PAWCTRL_API void __stdcall SetPolicyURL( char ** URLpolicy, __int32 noURL)
 {

for ( int i = 0; i < noURL; i++)
     {

    URLvector.push_back(URLpolicy[i]);
  }
 }

Please can any one help me how i should pass the function

thanks InAdvance

Hans Passant · Accepted Answer · 2012-05-03 11:46:44Z

1

CharSet = CharSet.Auto is wrong, it must be CharSet.Ansi to be compatible with a char* in native code. Use the debugger with unmanaged debugging enabled if you still have trouble, set a breakpoint on the function's first statement.

Also drop [PreserveSig], it has no meaning here. And SetLastError is very likely to be wrong, that's only typical on Windows api functions.

answered May 3, 2012 at 11:46

Hans Passant

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BSalita · Accepted Answer · 2016-01-16 15:57:42Z

Example passing string array from VB.Net to C. Compatible with 32 and 64 bit.

VB.Net:

Private Declare Function main_net32 Lib "MyCLib32.dll" Alias "_main_net@8" (ByVal argc As Int32, ByRef sArgs() As String) As Int32
Private Declare Function main_net64 Lib "MyCLib64.dll" Alias "main_net" (ByVal argc As Int32, ByRef sArgs() As String) As Int32

Private Sub MainWindow_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
    Dim sArgs() As String = Environment.GetCommandLineArgs
    Dim result As Int32
    If Environment.Is64BitProcess Then
        result = main_net64(sArgs.Length, sArgs)
    Else
        result = main_net32(sArgs.Length, sArgs)
    End If
End Sub

C:

#define DllExport(result) __declspec(dllexport) result __stdcall
DllExport(int) main_net(int argc, char ***argv)
{
    int i;
    for(i=0;i<argc;i++)
        printf("%d: %s",i,(*argv)[i]);
}

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