C# 如何从VB.Net或C中传递LPCSTR*以使用ActainUserAgentString

这是我的代码，我得到了错误输入参数

Imports System.Runtime.InteropServices

Module Module1
    Private Declare Function ObtainUserAgentString Lib "urlmon.dll" (ByVal dwOption As Integer, ByRef pcszUAOut As String, ByRef cbSize As Integer) As Integer
    Sub Main()
        Dim c As String
        Dim ptr As IntPtr = Marshal.StringToHGlobalUni(c)
        Dim useragent As String
        Dim size As Integer
        Dim result As Integer
        result = ObtainUserAgentString(0, useragent, size)

        'Try
        'result = ObtainUserAgentString(0, ptr, size)
        'Finally
        '    Marshal.FreeHGlobal(ptr)
        '    'End Try
    End Sub
End Module

显示

actainUserAgentString

函数定义为：

c#

[DllImport（ExternDll.Urlmon，ExactSpelling=true，CharSet=System.Runtime.InteropServices.CharSet.Ansi，BestFitMapping=false，ThrowOnUnmappableChar=true）]
私有静态外部MS.Internal.Interop.HRESULT获取用户代理字符串（int-dwOption，StringBuilder-userAgent，ref-int-length）；

vb.net

_
私有共享函数获取UserAgentString（dwOption为整数，userAgent为StringBuilder，ByRef长度为整数）为MS.Internal.Interop.HRESULT
端函数

所以你问题的答案是