運算符+不能應用於IntPtr和int類型的操作數-.Net 3.5

Question

以下代碼（用於查找DNS TXT記錄）在.NET 4中工作正常，但是由於各種原因，我不得不將項目降級到.NET 3.5，現在出現了一些錯誤

public String DnsGetTxtRecord(String name) {
  const Int16 DNS_TYPE_TEXT = 0x0010;
  const Int32 DNS_QUERY_STANDARD = 0x00000000;
  const Int32 DNS_ERROR_RCODE_NAME_ERROR = 9003;
  const Int32 DNS_INFO_NO_RECORDS = 9501;
  var queryResultsSet = IntPtr.Zero;
  try {
    var dnsStatus = DnsQuery(
      name,
      DNS_TYPE_TEXT,
      DNS_QUERY_STANDARD,
      IntPtr.Zero,
      ref queryResultsSet,
      IntPtr.Zero
    );
    if (dnsStatus == DNS_ERROR_RCODE_NAME_ERROR || dnsStatus == DNS_INFO_NO_RECORDS)
      return null;
    if (dnsStatus != 0)
      throw new Win32Exception(dnsStatus);
    DnsRecordTxt dnsRecord;
    for (var pointer = queryResultsSet; pointer != IntPtr.Zero; pointer = dnsRecord.pNext) {
      dnsRecord = (DnsRecordTxt) Marshal.PtrToStructure(pointer, typeof(DnsRecordTxt));
      if (dnsRecord.wType == DNS_TYPE_TEXT) {
        var lines = new List<String>();
        var stringArrayPointer = pointer
          + Marshal.OffsetOf(typeof(DnsRecordTxt), "pStringArray").ToInt32();
        for (var i = 0; i < dnsRecord.dwStringCount; ++i) {
          var stringPointer = (IntPtr) Marshal.PtrToStructure(stringArrayPointer, typeof(IntPtr));
          lines.Add(Marshal.PtrToStringUni(stringPointer));
          stringArrayPointer += IntPtr.Size;
        }
        return String.Join(Environment.NewLine, lines);
      }
    }
    return null;
  }
  finally {
    const Int32 DnsFreeRecordList = 1;
    if (queryResultsSet != IntPtr.Zero)
      DnsRecordListFree(queryResultsSet, DnsFreeRecordList);
  }
}

[DllImport("Dnsapi.dll", EntryPoint = "DnsQuery_W", ExactSpelling = true, CharSet = CharSet.Unicode, SetLastError = true)]
static extern Int32 DnsQuery(String lpstrName, Int16 wType, Int32 options, IntPtr pExtra, ref IntPtr ppQueryResultsSet, IntPtr pReserved);

[DllImport("Dnsapi.dll")]
static extern void DnsRecordListFree(IntPtr pRecordList, Int32 freeType);

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
struct DnsRecordTxt {
  public IntPtr pNext;
  public String pName;
  public Int16 wType;
  public Int16 wDataLength;
  public Int32 flags;
  public Int32 dwTtl;
  public Int32 dwReserved;
  public Int32 dwStringCount;
  public String pStringArray;
}

var stringArrayPointer = pointer + Marshal.OffsetOf(typeof(DnsRecordTxt), "pStringArray").ToInt32(); 觸發“運算符+不能應用於操作數IntPtr和int

return String.Join(Environment.NewLine, lines); 返回“最佳重載方法具有一些無效參數”

協助表示贊賞！

Answer 1

這個

var stringArrayPointer = pointer + Marshal.OffsetOf(typeof(DnsRecordTxt), "pStringArray").ToInt32();

可以更改為

var stringArrayPointer = (IntPtr)((long)pointer + Marshal.OffsetOf(typeof(DnsRecordTxt), "pStringArray").ToInt32());

（在.NET 4.0中，他們向IntPtr添加了一些基本操作，但在.NET 2.0 / 3.5中，您必須將其int轉換為int / long 。強制轉換為long更為安全，因為它已支持64位）

這個

return String.Join(Environment.NewLine, lines);

至

return String.Join(Environment.NewLine, lines.ToArray());

（在.NET 4.0中，他們添加了String.Join重載，該重載接受了IEnumerable<string>作為參數。在.NET 2.0 / 3.5中，您必須使用接受string[]的重載）

Answer 2

您不能添加到IntPtr ，但是您可以這樣做：

long address = pointer.ToInt64()
             + Marshal.OffsetOf(typeof(DnsRecordTxt), "pStringArray").ToInt64();
var stringArrayPointer = (IntPtr)address;

（正如@xanatos在他的回答中說的那樣，使用ToInt64而不是ToInt32使其在x64和x86中都可以工作。）

---

至於String.Join的問題，您需要向其傳遞一個數組作為第二個參數：

string.Join(Environment.NewLine, lines.ToArray());