Question

在C＃中使用int*之类的指针时，需要使用unsafe关键字，但是当使用IntPtr时，则不需要。这些有什么区别？他们都可以指向一个地址。

垃圾收集器如何处理这两种类型？他们的处理方式不同吗？如果是这样，有什么区别？如果没有，为什么需要unsafe关键字？

编辑：到目前为止，非常感谢每个人的答案，但我想知道的是框架和垃圾收集器对它们的处理方式有何不同，而不是MS {{{{{{ 1}}。只需要一次谷歌搜索即可。我想知道为什么IntPtr不需要IntPtr关键字？我想了解为什么我们可以在没有关键字的情况下使用它。

Answer 1

根据MSDN：

http://msdn.microsoft.com/en-gb/library/system.intptr(v=vs.100).aspx

它只是“指针或句柄”的表示。

我一直在研究GC如何处理IntPtr与其他托管类型的不同，我没有找到任何文档或文章说明IntPtr的收集方式不同，即，只要IntPtr超出范围，就可以进行GC。

关于没有使用unsafe关键字的原因，请阅读已接受的答案，尤其是更新：

Does unsafe code have any effect on safe code?

unsafe已在IntPtr的实现中指定（请参阅下面IntPtr实现中的字段声明），因此使用IntPtr的类没有标记它IntPtr使用unsafe的任何用法，否则它将一直级联到其他类，这些类可能使用在其实现中具有不安全代码的类型。

除了unsafe代码不是IntPtr之外，private unsafe void* m_value;字段unsafe并且您没有直接使用它。

// Type: System.IntPtr
// Assembly: mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
// Assembly location: C:\Windows\Microsoft.NET\Framework\v4.0.30319\mscorlib.dll

using System.Globalization;
using System.Runtime;
using System.Runtime.ConstrainedExecution;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;
using System.Security;

namespace System
{
  [ComVisible(true)]
  [__DynamicallyInvokable]
  [Serializable]
  public struct IntPtr : ISerializable
  {
    [SecurityCritical]
    private unsafe void* m_value;
    public static readonly IntPtr Zero;

    [__DynamicallyInvokable]
    public static int Size
    {
      [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success), TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries"), __DynamicallyInvokable] get
      {
        return 4;
      }
    }

    [SecuritySafeCritical]
    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    [__DynamicallyInvokable]
    public IntPtr(int value)
    {
      this.m_value = (void*) value;
    }

    [SecuritySafeCritical]
    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    [__DynamicallyInvokable]
    public IntPtr(long value)
    {
      this.m_value = (void*) checked ((int) value);
    }

    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    [SecurityCritical]
    [CLSCompliant(false)]
    [TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
    public IntPtr(void* value)
    {
      this.m_value = value;
    }

    [SecurityCritical]
    private IntPtr(SerializationInfo info, StreamingContext context)
    {
      long int64 = info.GetInt64("value");
      if (IntPtr.Size == 4 && (int64 > (long) int.MaxValue || int64 < (long) int.MinValue))
        throw new ArgumentException(Environment.GetResourceString("Serialization_InvalidPtrValue"));
      this.m_value = (void*) int64;
    }

    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    public static explicit operator IntPtr(int value)
    {
      return new IntPtr(value);
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    public static explicit operator IntPtr(long value)
    {
      return new IntPtr(value);
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    [SecurityCritical]
    [CLSCompliant(false)]
    public static explicit operator IntPtr(void* value)
    {
      return new IntPtr(value);
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [SecuritySafeCritical]
    [CLSCompliant(false)]
    public static explicit operator void*(IntPtr value)
    {
      return value.ToPointer();
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [SecuritySafeCritical]
    public static explicit operator int(IntPtr value)
    {
      return (int) value.m_value;
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [SecuritySafeCritical]
    public static explicit operator long(IntPtr value)
    {
      return (long) (int) value.m_value;
    }

    [SecuritySafeCritical]
    [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    public static bool operator ==(IntPtr value1, IntPtr value2)
    {
      return value1.m_value == value2.m_value;
    }

    [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [SecuritySafeCritical]
    public static bool operator !=(IntPtr value1, IntPtr value2)
    {
      return value1.m_value != value2.m_value;
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    public static IntPtr operator +(IntPtr pointer, int offset)
    {
      return new IntPtr(pointer.ToInt32() + offset);
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    public static IntPtr operator -(IntPtr pointer, int offset)
    {
      return new IntPtr(pointer.ToInt32() - offset);
    }

    [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
    [SecuritySafeCritical]
    internal unsafe bool IsNull()
    {
      return (IntPtr) this.m_value == IntPtr.Zero;
    }

    [SecurityCritical]
    unsafe void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
    {
      if (info == null)
        throw new ArgumentNullException("info");
      info.AddValue("value", (long) (int) this.m_value);
    }

    [SecuritySafeCritical]
    [__DynamicallyInvokable]
    public override unsafe bool Equals(object obj)
    {
      if (obj is IntPtr)
        return this.m_value == ((IntPtr) obj).m_value;
      else
        return false;
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [SecuritySafeCritical]
    [__DynamicallyInvokable]
    public override unsafe int GetHashCode()
    {
      return (int) this.m_value;
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [SecuritySafeCritical]
    [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
    [__DynamicallyInvokable]
    public unsafe int ToInt32()
    {
      return (int) this.m_value;
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [SecuritySafeCritical]
    [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
    [__DynamicallyInvokable]
    public unsafe long ToInt64()
    {
      return (long) (int) this.m_value;
    }

    [SecuritySafeCritical]
    [__DynamicallyInvokable]
    public override unsafe string ToString()
    {
      return ((int) this.m_value).ToString((IFormatProvider) CultureInfo.InvariantCulture);
    }

    [SecuritySafeCritical]
    [__DynamicallyInvokable]
    public unsafe string ToString(string format)
    {
      return ((int) this.m_value).ToString(format, (IFormatProvider) CultureInfo.InvariantCulture);
    }

    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    public static IntPtr Add(IntPtr pointer, int offset)
    {
      return pointer + offset;
    }

    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    [ReliabilityContract(Consistency.MayCorruptInstance, Cer.MayFail)]
    public static IntPtr Subtract(IntPtr pointer, int offset)
    {
      return pointer - offset;
    }

    [SecuritySafeCritical]
    [CLSCompliant(false)]
    [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
    [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
    public unsafe void* ToPointer()
    {
      return this.m_value;
    }
  }
}

Answer 2

IntPtr是一种托管类型，用于获取Windows操作系统的本机句柄。你不应该把它与像int*这样的实际指针混淆。

有关详细信息，请参阅MSDN。

Answer 3

IntPtr本质上只是指针类型的托管表示。您可以在不安全的上下文中自由地将任何指针类型转换为IntPtr。基本上IntPtr只是void*周围的薄包装（IIRC包含私有void*字段）。

通常在非托管代码（通过PInvoke或Marshal类）的互操作期间作为非托管指针类型的就地替换，就像指针一样IntPtr的大小因架构而异（x86系统为4个字节，x64为8个字节）。

Answer 4

一个相关的问题......为什么dllimport不需要不安全的背景？

我怀疑IntPtr和dllimport不需要不安全的上下文的原因是启用VB.NET（没有不安全）来轻松访问本机API。

然而，关于dllimport，IntPtr及其相互作用肯定存在“不安全”。

将无效参数传递给dllimport入口点会导致崩溃，或者更糟糕的是，无声地破坏内存。这意味着任何执行dllimport的代码在我看来都是“不安全的”。此外，如果该代码将IntPtr从安全代码泄漏到dllimport入口点，它基本上泄露了它“安全”代码中的“不安全”，因为安全代码可以修改IntPtr以使其无效。

当我使用dllimport时，我更喜欢将指针键入为unsafe-struct指针，而不是IntPtr。这有两大好处。首先，它为我提供了不同类型的本机指针的类型检查。其次，它可以防止危险的非托管本机指针泄漏到“安全”代码中。

http://www.codeproject.com/script/Articles/ArticleVersion.aspx?aid=339290&av=638710

http://software.1713.n2.nabble.com/using-unsafe-struct-instead-of-IntPtr-with-PInvoke-td5861023.html

为什么IntPtr不需要unsafe关键字？

4 个答案: