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带有LayoutKind.Explicit的布尔编组,这是否已损坏或按设计失败?

layoutkind.explicit marshalling boolean pinvoke c#

csharptest.net · 技术社区 · 15 年前

首先,据说布尔类型具有四字节值的默认封送处理类型。因此,以下代码起作用:

    struct A 
    { 
        public bool bValue1; 
        public int iValue2; 
    }
    struct B 
    { 
        public int iValue1;
        public bool bValue2; 
    }
    public static void Main()
    {
        int[] rawvalues = new int[] { 2, 4 };

        A a = (A)Marshal.PtrToStructure(GCHandle.Alloc(rawvalues, GCHandleType.Pinned).AddrOfPinnedObject(), typeof(A));
        Assert.IsTrue(a.bValue1 == true);
        Assert.IsTrue(a.iValue2 == 4);
        B b = (B)Marshal.PtrToStructure(GCHandle.Alloc(rawvalues, GCHandleType.Pinned).AddrOfPinnedObject(), typeof(B));
        Assert.IsTrue(b.iValue1 == 2);
        Assert.IsTrue(b.bValue2 == true);
    }

很明显,这些结构独立地运作得很好。这些值将按预期进行转换。但是,当我们通过声明LayoutKind.Explicit将这些结构组合成一个“联合”时,如下所示:

    [StructLayout(LayoutKind.Explicit)]
    struct Broken
    {
        [FieldOffset(0)]
        public A a;
        [FieldOffset(0)]
        public B b;
    }

我们突然发现自己无法正确编组这些类型。以下是上述结构的测试代码及其故障原因:

        int[] rawvalues = new int[] { 2, 4 };
        Broken broken = (Broken)Marshal.PtrToStructure(GCHandle.Alloc(rawvalues, GCHandleType.Pinned).AddrOfPinnedObject(), typeof(Broken));

        Assert.IsTrue(broken.a.bValue1 != false);// pass, not false
        Assert.IsTrue(broken.a.bValue1 == true);// pass, must be true?
        Assert.IsTrue(true.Equals(broken.a.bValue1));// FAILS, WOW, WTF?
        Assert.IsTrue(broken.a.iValue2 == 4);// FAILS, a.iValue1 == 1, What happened to 4?
        Assert.IsTrue(broken.b.iValue1 == 2);// pass
        Assert.IsTrue(broken.b.bValue2 == true);// pass

把这句话看作是真的是很幽默的:(a.bValue1!=false&a.bValue1==true&true.Equals(a.bValue1))

当然这里更大的问题是a.iValue2!=4,而是将4更改为1(可能是由于重叠布尔)。

所以问题是:这是一个bug,还是只是按照设计失败了?

背景:这来自 What is the difference between structures containing bool vs uint when using PInvoke?

更新:当您使用大整数值(>255)时,这就更奇怪了,因为只有用于布尔值的字节被修改为1,从而将b.bValue2的0x0f00更改为0x0f01。对于上面的a.bValue1,它根本不会被转换,0x0f00为a.bValue1提供了一个假值。

上述问题最明显、最合理的解决方案是使用uint进行编组,并公开布尔属性。用“变通办法”真正解决问题是毫无疑问的。我最想知道的是,这是一个bug还是你期望的行为?

    struct A 
    { 
        private uint _bValue1;
        public bool bValue1 { get { return _bValue1 != 0; } } 
        public int iValue2; 
    }
    struct B 
    { 
        public int iValue1;
        private uint _bValue2;
        public bool bValue2 { get { return _bValue2 != 0; } } 
    }

3 回复 | 直到 7 年前

earlNameless 15 年前

以下是正在发生的事情:

取新的int[]{2,4},让我们将其编组为A、B、breaked和brokern2。

如果我们将int封送到这些结构中,我们将在内存中获得以下值:

A:1,4
坏掉的:2,1
经纪人2:1,4

因此,发生的情况如下:

当封送拆收器遇到布尔值时,其值为:bool=(original!=0);

对于A,第一个int被转换成1,对于B,第二个int被转换成1, 对于breake,由于B是最后一个字段,因此其规则适用,因此第二个int被转换为1。Brokern2的情况也类似。

Gonzalo 15 年前

注释为“FAILS,WOW,WTF?”的行由于执行布尔比较的方式而失败。它将2与1进行比较:

IL_007e:  ldc.i4.1
IL_007f:  ldloca.s 3
IL_0081:  ldflda valuetype Test/A Test/Broken::a
IL_0086:  ldfld bool Test/A::bValue1
IL_008b:  ceq

ceq 最后将1与bValue中的字节(即2)进行比较。

有趣的是将测试“true”,因为它不是零。

至于另一个问题(breaked.a.iValue2==4),当我申请时,它消失了:

[MarshalAs (UnmanagedType.Bool)]

到结构中的两个布尔字段。这确保布尔值被封送为整数(在.NET中为4字节)。

csharptest.net 15 年前

这似乎是正确的,因为添加了另一个ints结构:

    struct C
    {
        public int iValue1;
        public int iValue2;
    }

[Serializable]
[ComVisible(true)]
public struct BOOL : IComparable, IConvertible, IComparable<BOOL>, IEquatable<BOOL>, IComparable<bool>, IEquatable<bool>
{
    private uint _data;

    public BOOL(bool value) { _data = value ? 1u : 0u; }
    public BOOL(int value) { _data = unchecked((uint)value); }
    public BOOL(uint value) { _data = value; }

    private bool Value { get { return _data != 0; } }
    private IConvertible Convertible { get { return _data != 0; } }

    #region IComparable Members
    public int CompareTo(object obj) { return Value.CompareTo(obj); }
    #endregion
    #region IConvertible Members
    public TypeCode GetTypeCode() { return Value.GetTypeCode(); }
    public string ToString(IFormatProvider provider) { return Value.ToString(provider); }
    bool IConvertible.ToBoolean(IFormatProvider provider) { return Convertible.ToBoolean(provider); }
    byte IConvertible.ToByte(IFormatProvider provider) { return Convertible.ToByte(provider); }
    char IConvertible.ToChar(IFormatProvider provider) { return Convertible.ToChar(provider); }
    DateTime IConvertible.ToDateTime(IFormatProvider provider) { return Convertible.ToDateTime(provider); }
    decimal IConvertible.ToDecimal(IFormatProvider provider) { return Convertible.ToDecimal(provider); }
    double IConvertible.ToDouble(IFormatProvider provider) { return Convertible.ToDouble(provider); }
    short IConvertible.ToInt16(IFormatProvider provider) { return Convertible.ToInt16(provider); }
    int IConvertible.ToInt32(IFormatProvider provider) { return Convertible.ToInt32(provider); }
    long IConvertible.ToInt64(IFormatProvider provider) { return Convertible.ToInt64(provider); }
    sbyte IConvertible.ToSByte(IFormatProvider provider) { return Convertible.ToSByte(provider); }
    float IConvertible.ToSingle(IFormatProvider provider) { return Convertible.ToSingle(provider); }
    ushort IConvertible.ToUInt16(IFormatProvider provider) { return Convertible.ToUInt16(provider); }
    uint IConvertible.ToUInt32(IFormatProvider provider) { return Convertible.ToUInt32(provider); }
    ulong IConvertible.ToUInt64(IFormatProvider provider) { return Convertible.ToUInt64(provider); }
    object IConvertible.ToType(Type conversionType, IFormatProvider provider) { return Convertible.ToType(conversionType, provider); }
    #endregion
    #region IComparable<bool> Members
    public int CompareTo(BOOL other) { return Value.CompareTo(other.Value); }
    public int CompareTo(bool other) { return Value.CompareTo(other); }
    #endregion
    #region IEquatable<bool> Members
    public bool Equals(BOOL other) { return Value.Equals(other.Value); }
    public bool Equals(bool other) { return Value.Equals(other); }
    #endregion
    #region Object Override
    public override string ToString() { return Value.ToString(); }
    public override int GetHashCode() { return Value.GetHashCode(); }
    public override bool Equals(object obj) { return Value.Equals(obj); }
    #endregion
    #region implicit/explicit cast operators
    public static implicit operator bool(BOOL value) { return value.Value; }
    public static implicit operator BOOL(bool value) { return new BOOL(value); }
    public static explicit operator int(BOOL value) { return unchecked((int)value._data); }
    public static explicit operator BOOL(int value) { return new BOOL(value); }
    public static explicit operator uint(BOOL value) { return value._data; }
    public static explicit operator BOOL(uint value) { return new BOOL(value); }
    #endregion
    #region +, -, !, ~, ++, --, true, false unary operators overloaded.
    public static BOOL operator !(BOOL b) { return new BOOL(!b.Value); }
    public static bool operator true(BOOL b) { return b.Value; }
    public static bool operator false(BOOL b) { return !b.Value; }
    #endregion
    #region +, -, *, /, %, &, |, ^, <<, >> binary operators overloaded.
    public static BOOL operator &(BOOL b1, BOOL b2) { return new BOOL(b1.Value & b2.Value); }
    public static BOOL operator |(BOOL b1, BOOL b2) { return new BOOL(b1.Value | b2.Value); }
    #endregion
    #region ==, !=, <, >, <=, >= comparison operators overloaded
    public static bool operator ==(BOOL b1, BOOL b2) { return (b1.Value == b2.Value); }
    public static bool operator !=(BOOL b1, BOOL b2) { return (b1.Value != b2.Value); }
    #endregion
}