将偏移量添加到 IntPtr

Question

我正在寻找一种在 C# 或 .NET 中执行指针操作的方法。

我想做一些非常简单的事情

有一个指针 IntPtr 我想获得指向前面 2 个字节的 IntPtr 对象。

我读了一些帖子，说下面的代码片段会起作用...

IntPtr ptr = new IntPtr(oldptr.ToInt32() + 2);

但我怀疑这个语句是否也适用于 64 位机器（因为寻址是 64 位的）..

我发现了这种优雅的方法来添加偏移量，但是不幸的是仅在.NET 4.0中 http: //msdn.microsoft.com/en-us/library/system.intptr.add%28VS.100%29.aspx

Answer 1

在 .net 4 中添加了静态 Add() 和 Subtract() 方法。

IntPtr ptr = IntPtr.Add(oldPtr, 2);

http://msdn.microsoft.com/en-us/library /system.intptr.add.aspx

Answer 2

我建议您使用 ToInt64() 和 long 来执行计算。这样您就可以避免 64 位版本的 .NET 框架出现问题。

IntPtr ptr = new IntPtr(oldptr.ToInt64() + 2);

这在 32 位系统上增加了一点开销，但更安全。

Answer 3

对于 C# 中的指针算术，您应该在 unsafe 上下文中使用正确的指针：

class PointerArithmetic
{
    unsafe static void Main() 
    {
        int* memory = stackalloc int[30];
        long* difference;
        int* p1 = &memory[4];
        int* p2 = &memory[10];

        difference = (long*)(p2 - p1);

        System.Console.WriteLine("The difference is: {0}", (long)difference);
    }
}

IntPtr 类型用于传递句柄或指针，也用于编组到支持指针的语言。但它不适用于指针算术。

Answer 4

我发现我可以通过使用 Marshal.ReadByte()、Marshal.ReadInt16() 等方法来避免指针操作。这组方法允许指定与 IntPtr 相关的偏移量...

Answer 5

public static class IntPtrExtensions
{
    #region Methods: Arithmetics
    public static IntPtr Decrement(this IntPtr pointer, Int32 value)
    {
        return Increment(pointer, -value);
    }

    public static IntPtr Decrement(this IntPtr pointer, Int64 value)
    {
        return Increment(pointer, -value);
    }

    public static IntPtr Decrement(this IntPtr pointer, IntPtr value)
    {
        switch (IntPtr.Size)
        {
            case sizeof(Int32):
                return (new IntPtr(pointer.ToInt32() - value.ToInt32()));

            default:
                return (new IntPtr(pointer.ToInt64() - value.ToInt64()));
        }
    }

    public static IntPtr Increment(this IntPtr pointer, Int32 value)
    {
        unchecked
        {
            switch (IntPtr.Size)
            {
                case sizeof(Int32):
                    return (new IntPtr(pointer.ToInt32() + value));

                default:
                    return (new IntPtr(pointer.ToInt64() + value));
            }
        }
    }

    public static IntPtr Increment(this IntPtr pointer, Int64 value)
    {
        unchecked
        {
            switch (IntPtr.Size)
            {
                case sizeof(Int32):
                    return (new IntPtr((Int32)(pointer.ToInt32() + value)));

                default:
                    return (new IntPtr(pointer.ToInt64() + value));
            }
        }
    }

    public static IntPtr Increment(this IntPtr pointer, IntPtr value)
    {
        unchecked
        {
            switch (IntPtr.Size)
            {
                case sizeof(int):
                    return new IntPtr(pointer.ToInt32() + value.ToInt32());
                default:
                    return new IntPtr(pointer.ToInt64() + value.ToInt64());
            }
        }
    }
    #endregion

    #region Methods: Comparison
    public static Int32 CompareTo(this IntPtr left, Int32 right)
    {
        return left.CompareTo((UInt32)right);
    }

    public static Int32 CompareTo(this IntPtr left, IntPtr right)
    {
        if (left.ToUInt64() > right.ToUInt64())
            return 1;

        if (left.ToUInt64() < right.ToUInt64())
            return -1;

        return 0;
    }

    public static Int32 CompareTo(this IntPtr left, UInt32 right)
    {
        if (left.ToUInt64() > right)
            return 1;

        if (left.ToUInt64() < right)
            return -1;

        return 0;
    }
    #endregion

    #region Methods: Conversion
    public unsafe static UInt32 ToUInt32(this IntPtr pointer)
    {
        return (UInt32)((void*)pointer);
    }

    public unsafe static UInt64 ToUInt64(this IntPtr pointer)
    {
        return (UInt64)((void*)pointer);
    }
    #endregion

    #region Methods: Equality
    public static Boolean Equals(this IntPtr pointer, Int32 value)
    {
        return (pointer.ToInt32() == value);
    }

    public static Boolean Equals(this IntPtr pointer, Int64 value)
    {
        return (pointer.ToInt64() == value);
    }

    public static Boolean Equals(this IntPtr left, IntPtr ptr2)
    {
        return (left == ptr2);
    }

    public static Boolean Equals(this IntPtr pointer, UInt32 value)
    {
        return (pointer.ToUInt32() == value);
    }

    public static Boolean Equals(this IntPtr pointer, UInt64 value)
    {
        return (pointer.ToUInt64() == value);
    }

    public static Boolean GreaterThanOrEqualTo(this IntPtr left, IntPtr right)
    {
        return (left.CompareTo(right) >= 0);
    }

    public static Boolean LessThanOrEqualTo(this IntPtr left, IntPtr right)
    {
        return (left.CompareTo(right) <= 0);
    }
    #endregion

    #region Methods: Logic
    public static IntPtr And(this IntPtr pointer, IntPtr value)
    {
        switch (IntPtr.Size)
        {
            case sizeof(Int32):
                return (new IntPtr(pointer.ToInt32() & value.ToInt32()));

            default:
                return (new IntPtr(pointer.ToInt64() & value.ToInt64()));
        }
    }

    public static IntPtr Not(this IntPtr pointer)
    {
        switch (IntPtr.Size)
        {
            case sizeof(Int32):
                return (new IntPtr(~pointer.ToInt32()));

            default:
                return (new IntPtr(~pointer.ToInt64()));
        }
    }

    public static IntPtr Or(this IntPtr pointer, IntPtr value)
    {
        switch (IntPtr.Size)
        {
            case sizeof(Int32):
                return (new IntPtr(pointer.ToInt32() | value.ToInt32()));

            default:
                return (new IntPtr(pointer.ToInt64() | value.ToInt64()));
        }
    }

    public static IntPtr Xor(this IntPtr pointer, IntPtr value)
    {
        switch (IntPtr.Size)
        {
            case sizeof(Int32):
                return (new IntPtr(pointer.ToInt32() ^ value.ToInt32()));

            default:
                return (new IntPtr(pointer.ToInt64() ^ value.ToInt64()));
        }
    }
    #endregion
}

Answer 6

您可以使用扩展方法：

public static IntPtrExtensions {
    public static IntPtr Add( this IntPtr ptr, int offSet ) {
        IntPtr ret = new IntPtr( ptr.ToInt64() + offSet );
        return ret;
    }
}
// ... somewhere else ...
IntPtr pointer = GetHandle().Add( 15 );