8

当你int*在 C# 中使用指针时，你需要使用unsafe关键字，但是当你使用 时IntPtr，你不需要。这些有什么区别？它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？如果不是，为什么需要unsafe关键字？

编辑：非常感谢到目前为止大家的回答，但我想知道的是框架和垃圾收集器如何以不同方式处理它们，而不是 MSDN 定义的IntPtr. 只需一次谷歌搜索即可到达那里。我想知道为什么 IntPtr 不需要unsafe关键字？我想了解我们可以在没有关键字的情况下使用它的原因。

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4 回答 4

5

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。

我一直在阅读IntPtrGC 处理 GC 与其他托管类型的不同方式，但我没有找到任何文档或文章说明IntPtr收集的方式有什么不同，即一旦IntPtr超出范围，它就可以是 GC 'd。

关于为什么不使用unsafe关键字阅读已接受的答案，尤其是更新：

不安全代码对安全代码有影响吗？

unsafe已经在的实现中指定IntPtr（参见IntPtr下面实现中的字段声明），因此使用 的类IntPtr不必将它的任何使用标记IntPtr为unsafe也使用，否则它将一直级联到其他类可能会在其实现中使用具有不安全代码的类型。

除了unsafecode is not之外IntPtr，它是字段private unsafe void* m_value;并且unsafe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;
    }
  }
}
于 2013-02-22T11:06:36.330 回答
1

IntPtr 是一种托管类型，用于获取 Windows 操作系统的本机句柄。您不应该将它与像int*.

请参阅MSDN以获取更多参考。

于 2013-02-22T11:06:29.893 回答
1

一个相关的问题......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（它没有不安全）能够轻松访问本机 API。

但是，关于 dllimport、IntPtr 及其交互，肯定存在一些“不安全”的地方。

将无效参数传递给 dllimport 入口点可能会导致崩溃，或者更糟糕的是，会默默地损坏内存。这意味着任何执行 dllimport 的代码在我看来都是“不安全的”。此外，如果该代码将安全代码中的 IntPtr 泄漏到 dllimport 入口点，则本质上是将其“不安全”泄漏到该安全代码中，因为安全代码可以修改 IntPtr 以使其无效。

当我使用 dllimport 时，我更喜欢将指针类型作为不安全结构指针，而不是 IntPtr。这有两大好处。首先，它让我对不同类型的本机指针进行类型检查。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

于 2013-08-20T07:08:12.863 回答
1

AnIntPtr本质上只是指针类型的托管表示。IntPtr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 an 。本质上， anIntPtr只是围绕 a 的一个薄包装器void*（IIRC 它包含一个私有void*字段）。

它通常在与非托管代码（通过PInvoke或Marshal类）互操作期间作为非托管指针类型的就地替换，因为像指针一样，IntPtr的大小随架构而变化（x86 系统上为 4 个字节，x64 上为 8 个字节）。

于 2013-02-22T11:10:36.217 回答