在C#中使用DLL

我正试图在C#窗体应用程序中使用一个旧的C DLL。似乎我对输出参数使用了错误的数据类型。

DLL源代码：

#ifdef __cplusplus
#define EXPORT extern "C" __declspec (dllexport)
#else
#define EXPORT __declspec (dllexport)
#endif
EXPORT INT CALLBACK Complemento (LPSTR) ;
EXPORT INT CALLBACK MatchCode (LPSTR, LPSTR, LPSTR, LPSTR);

c#DLL导出

[DllImport(
    @"<MYDIR>Fonetica.dll",
    CharSet = CharSet.Ansi)]
public static extern int MatchCode(
    String n,
    String s,
    String e,
    [MarshalAs(UnmanagedType.LPStr)] out String retorno);

C#DLL使用代码

String match = String.Empty;
MatchCode(pefi.Nome, String.Empty, String.Empty, out match);

树的第一个参数是输入的，最后一个参数是输出的。

我收到这个异常：

System.AccessViolationException was unhandled
  Message=Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
  Source=mscorlib
  StackTrace:
       at System.String..ctor(SByte* value)
       at System.StubHelpers.CSTRMarshaler.ConvertToManaged(IntPtr cstr)
       at WFMatchCode.Form1.MatchCode(String n, String s, String e, String& retorno)
       at WFMatchCode.Form1.button1_Click(Object sender, EventArgs e) in C:'Users'computecnica.alexand'Documents'Visual Studio 2010'Projects'WFMatchCode'WFMatchCode'Form1.cs:line 91
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at WFMatchCode.Program.Main() in c:'users'computecnica.alexand'documents'visual studio 2010'Projects'WFMatchCode'WFMatchCode'Program.cs:line 18
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

[DllImport( @"Fonetica.dll", CharSet = CharSet.Ansi)]
public static extern int MatchCode(String n, String s, String e, StringBuilder retorno);

var capacity = 1000; // change this to whatever you need
var buffer = new StringBuilder(capacity);
var result = MatchCode("test", "test", "test", buffer);
var output = buffer.ToString();