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

Question

这是我的代码，我收到错误的输入参数

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

Answer 1

Reference source 显示 ObtainUserAgentString 函数定义为：

c#

[DllImport(ExternDll.Urlmon, ExactSpelling = true, CharSet = System.Runtime.InteropServices.CharSet.Ansi, BestFitMapping = false, ThrowOnUnmappableChar = true)]
private static extern MS.Internal.Interop.HRESULT ObtainUserAgentString(int dwOption, StringBuilder userAgent, ref int length);

vb.net

<DllImport(ExternDll.Urlmon, ExactSpelling:=True, CharSet:=System.Runtime.InteropServices.CharSet.Ansi, BestFitMapping:=False, ThrowOnUnmappableChar:=True)> _
Private Shared Function ObtainUserAgentString(dwOption As Integer, userAgent As StringBuilder, ByRef length As Integer) As MS.Internal.Interop.HRESULT
End Function

所以你的问题的答案是StringBuilder。

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

How to pass LPCSTR * from VB.Net or C# to use ObtainUserAgentString

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