为什么IntPtr不需要unsafe关键字？

Question

在C＃中使用像int*这样的指针时，需要使用unsafe关键字，但是在使用IntPtr ，则不需要。 这些有什么区别？ 他们俩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？ 如果不是，为什么需要unsafe关键字？

编辑：到目前为止，非常感谢大家的回答，但是我想知道的是框架和垃圾收集器如何不同地处理它们，而不是IntPtr的MSDN定义。 只需进行一次Google搜索即可。 我想知道为什么IntPtr不需要unsafe关键字？ 我想了解没有关键字就可以使用它的原因。

Answer 1

根据MSDN：

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

它仅是“指针或句柄”的表示 。

我一直在阅读有关GC与其他托管类型如何不同地处理IntPtr ，并且我还没有发现任何说明IntPtr的收集方式有所不同的文档或文章，即，一旦IntPtr超出范围，它可以被GC。

关于为什么不使用unsafe关键字的原因，请阅读已接受的答案，尤其是更新内容：

不安全代码对安全代码有影响吗？

unsafe已经在执行指定IntPtr （见域声明IntPtr下面实现），因此，使用类IntPtr没有标记任何使用IntPtr它使用的unsafe也，否则会级联所有到其他可能在实现中使用不安全代码的类的类。

除了unsafe代码不是IntPtr ，它是字段private unsafe void* m_value; 这是unsafe ，您不能直接使用它。

// 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，即获取Windows OS的本机句柄。 您不应将其与int*这样的实际指针混淆。

有关更多参考，请参见MSDN 。

Answer 3

IntPtr本质上只是指针类型的托管表示形式。 您可以在不安全的上下文中将任何指针类型自由转换为IntPtr 。 本质上， IntPtr只是围绕void* （IIRC它包含一个私有void*字段）的薄包装。

通常在与非托管代码（通过PInvoke或Marshal类）进行互操作期间作为非托管指针类型的就地替换，因为就像指针一样， IntPtr的大小随体系结构而有所不同（x86系统上为4个字节，x64系统上为8个字节） ）。

Answer 4

一个相关问题...为什么dllimport不需要不安全的上下文？

我怀疑IntPtr和dllimport不需要不安全上下文的原因是使VB.NET（没有不安全）可以轻松访问本机API。

但是，对于dllimport，IntPtr及其交互，肯定存在某些“不安全”之处。

将无效的参数传递给dllimport入口点可能会导致崩溃，或更糟糕的是，无提示地破坏内存。 这意味着在我看来，任何执行dllimport的代码都是“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，则实质上是在安全代码中泄漏了“不安全”，因为安全代码可以修改IntPtr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。 这有两个好处。 首先，它使我可以检查不同类型的本机指针的类型。 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