Boolean和bool VS. 鸡蛋和鸡

    C/C++中没有提供bool类型，我们可以用0和非0取而代之；而在.Net中则提供了一个Boolean类型，其实是对0/1的一个封装。下面我们来看下这段代码：

Boolean b= true;
Console.WriteLine(sizeof(Boolean));//得到的结果是1byte
unsafe//先要用/unsafe(项目属性->Build->Allow unsafe code)来关闭安全检查
...{
    int i = (int)&b;//取地址
    Console.WriteLine(*(byte*)i);//上面得到bool类型占1byte，这里将Boolean中的值按byte来读取
}

    得出的结果是1，当Boolean变量b赋值为false时，得到的结果是0。虽然只用1个bit就可以表示0/1了，但计算机存储的最小单位是byte，没办法只好浪费另外7个bit了:)

 

    现在转入正题来扯淡，出于对Boolean的好奇，我用Reflector反汇编了下mscorlib.dll，得到Boolean的源代码(完整的代码见附录)，居然看到了下面的内容：

    public struct Boolean : IComparable, IConvertible, IComparable<bool>, IEquatable<bool>
    ...{
        private bool m_value;
        //省略其他成员的定义.....
    }

    MSDN中解释bool与Boolean的关系是：“bool 关键字是 System.Boolean 的别名”。观察上面的Boolean类型定义，在其继承的泛型接口和成员变量中，我们找到了“bool”的影子(我想可能时Reflector将IL代码反汇编时将类型Boolean翻译成C#中的关键字bool)，也就是说Boolean的定义依赖与bool(Boolean)。这就好比鸡蛋与鸡，到底是先有鸡蛋还是先有鸡？到底是先有Boolean的类型定义还是先有Boolean类型呢？ 


附录 - Boolean类源码：

  1namespace System
  2{
  3    using System.Globalization;
  4    using System.Runtime.InteropServices;
  5
  6    [Serializable, StructLayout(LayoutKind.Sequential), ComVisible(true)]
  7    public struct Boolean : IComparable, IConvertible, IComparable<bool>, IEquatable<bool>
  8    {
  9        internal const int True = 1;
 10        internal const int False = 0;
 11        internal const string TrueLiteral = "True";
 12        internal const string FalseLiteral = "False";
 13        private bool m_value;
 14        private static char[] m_trimmableChars;
 15        public static readonly string TrueString;
 16        public static readonly string FalseString;
 17        public override int GetHashCode()
 18        {
 19            if (!this)
 20            {
 21                return 0;
 22            }
 23            return 1;
 24        }
 25
 26        public override string ToString()
 27        {
 28            if (!this)
 29            {
 30                return "False";
 31            }
 32            return "True";
 33        }
 34
 35        public string ToString(IFormatProvider provider)
 36        {
 37            if (!this)
 38            {
 39                return "False";
 40            }
 41            return "True";
 42        }
 43
 44        public override bool Equals(object obj)
 45        {
 46            if (obj is bool)
 47            {
 48                return (this == ((bool) obj));
 49            }
 50            return false;
 51        }
 52
 53        public bool Equals(bool obj)
 54        {
 55            return (this == obj);
 56        }
 57
 58        public int CompareTo(object obj)
 59        {
 60            if (obj != null)
 61            {
 62                if (!(obj is bool))
 63                {
 64                    throw new ArgumentException(Environment.GetResourceString("Arg_MustBeBoolean"));
 65                }
 66                if (this == ((bool) obj))
 67                {
 68                    return 0;
 69                }
 70                if (!this)
 71                {
 72                    return -1;
 73                }
 74            }
 75            return 1;
 76        }
 77
 78        public int CompareTo(bool value)
 79        {
 80            if (this == value)
 81            {
 82                return 0;
 83            }
 84            if (!this)
 85            {
 86                return -1;
 87            }
 88            return 1;
 89        }
 90
 91        public static bool Parse(string value)
 92        {
 93            if (value == null)
 94            {
 95                throw new ArgumentNullException("value");
 96            }
 97            bool result = false;
 98            if (!TryParse(value, out result))
 99            {
100                throw new FormatException(Environment.GetResourceString("Format_BadBoolean"));
101            }
102            return result;
103        }
104
105        public static bool TryParse(string value, out bool result)
106        {
107            result = false;
108            if (value != null)
109            {
110                if ("True".Equals(value, StringComparison.OrdinalIgnoreCase))
111                {
112                    result = true;
113                    return true;
114                }
115                if ("False".Equals(value, StringComparison.OrdinalIgnoreCase))
116                {
117                    result = false;
118                    return true;
119                }
120                if (m_trimmableChars == null)
121                {
122                    char[] destinationArray = new char[string.WhitespaceChars.Length + 1];
123                    Array.Copy(string.WhitespaceChars, destinationArray, string.WhitespaceChars.Length);
124                    destinationArray[destinationArray.Length - 1] = '\0';
125                    m_trimmableChars = destinationArray;
126                }
127                value = value.Trim(m_trimmableChars);
128                if ("True".Equals(value, StringComparison.OrdinalIgnoreCase))
129                {
130                    result = true;
131                    return true;
132                }
133                if ("False".Equals(value, StringComparison.OrdinalIgnoreCase))
134                {
135                    result = false;
136                    return true;
137                }
138            }
139            return false;
140        }
141
142        public TypeCode GetTypeCode()
143        {
144            return TypeCode.Boolean;
145        }
146
147        bool IConvertible.ToBoolean(IFormatProvider provider)
148        {
149            return this;
150        }
151
152        char IConvertible.ToChar(IFormatProvider provider)
153        {
154            throw new InvalidCastException(string.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("InvalidCast_FromTo"), new object[] { "Boolean", "Char" }));
155        }
156
157        sbyte IConvertible.ToSByte(IFormatProvider provider)
158        {
159            return Convert.ToSByte(this);
160        }
161
162        byte IConvertible.ToByte(IFormatProvider provider)
163        {
164            return Convert.ToByte(this);
165        }
166
167        short IConvertible.ToInt16(IFormatProvider provider)
168        {
169            return Convert.ToInt16(this);
170        }
171
172        ushort IConvertible.ToUInt16(IFormatProvider provider)
173        {
174            return Convert.ToUInt16(this);
175        }
176
177        int IConvertible.ToInt32(IFormatProvider provider)
178        {
179            return Convert.ToInt32(this);
180        }
181
182        uint IConvertible.ToUInt32(IFormatProvider provider)
183        {
184            return Convert.ToUInt32(this);
185        }
186
187        long IConvertible.ToInt64(IFormatProvider provider)
188        {
189            return Convert.ToInt64(this);
190        }
191
192        ulong IConvertible.ToUInt64(IFormatProvider provider)
193        {
194            return Convert.ToUInt64(this);
195        }
196
197        float IConvertible.ToSingle(IFormatProvider provider)
198        {
199            return Convert.ToSingle(this);
200        }
201
202        double IConvertible.ToDouble(IFormatProvider provider)
203        {
204            return Convert.ToDouble(this);
205        }
206
207        decimal IConvertible.ToDecimal(IFormatProvider provider)
208        {
209            return Convert.ToDecimal(this);
210        }
211
212        DateTime IConvertible.ToDateTime(IFormatProvider provider)
213        {
214            throw new InvalidCastException(string.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("InvalidCast_FromTo"), new object[] { "Boolean", "DateTime" }));
215        }
216
217        object IConvertible.ToType(Type type, IFormatProvider provider)
218        {
219            return Convert.DefaultToType(this, type, provider);
220        }
221
222        static Boolean()
223        {
224            TrueString = "True";
225            FalseString = "False";
226        }
227    }
228}

转载于:https://www.cnblogs.com/happyhippy/archive/2007/04/12/710928.html