How I can marshal char** and char[] in VB .ne

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VB

Hello, I am trying to get data from C library into Vb using marshalling I am able to get data for - int,foat,char,char*...
I am unable to Marshal char[] and char**. Can you please help me to understand how can I do it..

What I have tried:

Header File

   extern struct listStandardTimeParameterAttributes {
        int index;
        int iMasterNum;
        float fValue;
        char parameterMethodName;
        char* strUnits;
        char AttrValu[256];
        char** lstAttrdata;
    };
extern "C"  struct ParameterAttributes_C
    {
        listStandardTimeParameterAttributes StandardTimeParameterAttributes;
        
 er;
    };

return code -

ParameterAttributes_C ReadFile_C(char* filename) {
        ParameterAttributes_C mParamNameAndValues;
        mParamNameAndValues.StandardTimeParameterAttributes.iMasterNum = 1;
        mParamNameAndValues.StandardTimeParameterAttributes.index = 10;
        mParamNameAndValues.StandardTimeParameterAttributes.fValue = 11.1112;
        char ch = 'h';
      mParamNameAndValues.StandardTimeParameterAttributes.parameterMethodName = ch;
        mParamNameAndValues.StandardTimeParameterAttributes.strUnits = new char[1024];
       strcpy_s(mParamNameAndValues.StandardTimeParameterAttributes.strUnits, 10, "Hello2");
        char attrsname[1024];
        strcpy_s(attrsname, 7,"Hello2");
        char** x ;
        int iCnt = 0;
        strcpy(x[iCnt], (char*)malloc(strlen(attrsname) * sizeof(char)));
        strcpy(mParamNameAndValues.StandardTimeParameterAttributes.lstAttrdata[iCnt], x[iCnt]);
        
        return mParamNameAndValues;
    }

VB code -

<pre><StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)>
    Public Structure listStandardTimeParameterAttributes
        Public index As Integer
        Public iMasterNum As Integer
        Public fValue As Single
        Public parameterMethodName As Byte
        Public strUnits As IntPtr
        <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=256)>
        Public AttrValu As String
        Public lstAttrdata As IntPtr
    End Structure

    <StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)>
    Public Structure ParameterAttributes_C
        Public StandardTimeParameterAttributes As listStandardTimeParameterAttributes
    End Structure

    Declare Function ReadFile_C Lib "C:\Users\source\repos\customLibrary\x64\Debug\customLibrary.dll" (ByVal filename As String) As ParameterAttributes_C

VB calling code -

Dim si As testDR.ParameterAttributes_C = testDR.ReadFile_C(txtShowPath.Text)
        MsgBox(si.StandardTimeParameterAttributes.iMasterNum, MsgBoxStyle.Information, "Return from Custom DLL") 'Integer
        MsgBox(si.StandardTimeParameterAttributes.index, MsgBoxStyle.Information, "Return from Custom DLL") 'Integer
        MsgBox(si.StandardTimeParameterAttributes.fValue, MsgBoxStyle.Information, "Return from Custom DLL") 'Float
        MsgBox(Convert.ToChar(si.StandardTimeParameterAttributes.parameterMethodName), MsgBoxStyle.Information, "Return from Custom DLL") 'Char
        Dim s1 As String = Marshal.PtrToStringAnsi(si.StandardTimeParameterAttributes.strUnits)
        MsgBox(s1, MsgBoxStyle.Information, "Return from Custom DLL") 'Char*

I tried couple of examples to marshal char[] and char** but it didn't worked.. can you please help me to understand how it can be done.