c# Equal函数 and 运算符'=='

1、==、!=、<、>、<= 和>= 运算符为比较运算符(comparison operator)。C#语言规范5.0中文版中比较运算符的描述如下：

2、通用类型系统

3、值类型Equal函数 and 运算符’==’

3.1、常见类型 int、float、double、decimal等虽然继承自ValueType，但其结构体内部重写了Equal。

3.1.1、 int，float，double，decimal内部的Equal函数和 ‘==’重载符函数。

        Int32        {            public override bool Equals(Object obj) {                if (!(obj is Int32)) {                    return false;                }                return m_value == ((Int32)obj).m_value;            }            [System.Runtime.Versioning.NonVersionable]            public bool Equals(Int32 obj)            {                return m_value == obj;            }                   }        Double        {            // True if obj is another Double with the same value as the current instance.  This is            // a method of object equality, that only returns true if obj is also a double.            public override bool Equals(Object obj) {                if (!(obj is Double)) {                    return false;                }                double temp = ((Double)obj).m_value;                // This code below is written this way for performance reasons i.e the != and == check is intentional.                if (temp == m_value) {                    return true;                }                return IsNaN(temp) && IsNaN(m_value);            }            public bool Equals(Double obj)            {                if (obj == m_value) {                    return true;                }                return IsNaN(obj) && IsNaN(m_value);            }                [System.Runtime.Versioning.NonVersionable]            public static bool operator ==(Double left, Double right) {                return left == right;            }                   }        Single        {            public override bool Equals(Object obj) {                if (!(obj is Single)) {                    return false;                }                float temp = ((Single)obj).m_value;                if (temp == m_value) {                    return true;                }                return IsNaN(temp) && IsNaN(m_value);            }            public bool Equals(Single obj)            {                if (obj == m_value) {                    return true;                }                return IsNaN(obj) && IsNaN(m_value);            }             [System.Runtime.Versioning.NonVersionable]            public static bool operator ==(Single left, Single right) {                return left == right;            }                   }        Decimal        {            // Checks if this Decimal is equal to a given object. Returns true            // if the given object is a boxed Decimal and its value is equal to the            // value of this Decimal. Returns false otherwise.            //            [System.Security.SecuritySafeCritical]  // auto-generated            public override bool Equals(Object value) {                if (value is Decimal) {                    Decimal other = (Decimal)value;                    return FCallCompare(ref this, ref other) == 0;                }                return false;            }            [System.Security.SecuritySafeCritical]  // auto-generated            public bool Equals(Decimal value)            {                return FCallCompare(ref this, ref value) == 0;            }               [System.Security.SecuritySafeCritical]  // auto-generated            public static bool operator ==(Decimal d1, Decimal d2) {                return FCallCompare(ref d1, ref d2) == 0;            }            //暂时不知道此函数内部代码，如有知道还望告知。            //根据测试结果，推测如果两个decimal数相等，返回0            [System.Security.SecurityCritical]  // auto-generated            [ResourceExposure(ResourceScope.None)]            [MethodImplAttribute(MethodImplOptions.InternalCall)]            [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]            private static extern int FCallCompare(ref Decimal d1, ref Decimal d2);            }

3.1.2、感兴趣的可去Reference Source 查看全部代码。

3.1.3、测试代码：

            //T is int 、float、double、decimal、byte、char            T a = 1234567890;//0.1234567890f、0.123456789、1234567890M、(byte)11、'a'            T b = 1234567890;//0.1234567890f、0.123456789、1234567890M、(byte)11、'a'            Console.WriteLine(a == b);//返回true            Console.WriteLine(a.Equals(b));//返回true            Console.WriteLine(a.Equals((object)b));//返回true            /*            Console.WriteLine((object)a == b);//编译错误：运算符‘==’无法应用与‘object’和‘T’类型操作数            Console.WriteLine(a == (object)b);//编译错误：运算符‘==’无法应用与‘object’和‘T’类型操作数            //Console.WriteLine((object)a == (object)b);//返回false，下面解释为什么是false。这个是引用类型'=='，放到下文介绍            */

3.1.4、结论：对于简单常见值类型 int、float、double、decimal等，Equal函数 and 运算符’==’，如果其值相等，返回true；否则，返回false。

3.2、 结构体struct

3.2.1、 ValueType内部的Equals函数

        ValueType        {            [System.Security.SecuritySafeCritical]            public override bool Equals (Object obj) {                BCLDebug.Perf(false, "ValueType::Equals is not fast.  "+this.GetType().FullName+" should override Equals(Object)");                if (null==obj) {                    return false;                }                RuntimeType thisType = (RuntimeType)this.GetType();                RuntimeType thatType = (RuntimeType)obj.GetType();                if (thatType!=thisType) {                    return false;                }                Object thisObj = (Object)this;                Object thisResult, thatResult;                // if there are no GC references in this object we can avoid reflection                 // and do a fast memcmp                if (CanCompareBits(this))                    return FastEqualsCheck(thisObj, obj);                FieldInfo[] thisFields = thisType.GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);                for (int i=0; i<thisFields.Length; i++) {                    thisResult = ((RtFieldInfo)thisFields[i]).UnsafeGetValue(thisObj);                    thatResult = ((RtFieldInfo)thisFields[i]).UnsafeGetValue(obj);                    if (thisResult == null) {                        if (thatResult != null)                            return false;                    }                    else                    if (!thisResult.Equals(thatResult)) {                        return false;                    }                }                return true;            }            [System.Security.SecuritySafeCritical]  // auto-generated            [ResourceExposure(ResourceScope.None)]            [MethodImplAttribute(MethodImplOptions.InternalCall)]            private static extern bool CanCompareBits(Object obj);            [System.Security.SecuritySafeCritical]  // auto-generated            [ResourceExposure(ResourceScope.None)]            [MethodImplAttribute(MethodImplOptions.InternalCall)]            private static extern bool FastEqualsCheck(Object a, Object b);                 }

3.2.2、结构体(只有值类型，重写Equal函数 and 运算符’==’)

3.2.2.1、测试代码：

    struct Point    {        public double x;        public double y;        public double z;        public Point(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }        public override bool Equals(Object obj)        {            if (!(obj is Point))            {                return false;            }            if (((Point)obj).x == this.x)            {                return true;            }            return false;        }        public bool Equals(Point obj)        {            if (obj.x == this.x)            {                return true;            }            return false;        }        //运算符“Point.operator ==(Point, Point)”要求也要定义匹配的运算符“!=”        public static bool operator ==(Point left, Point right)        {            return left.x == right.x;        }        public static bool operator !=(Point left, Point right)        {            return left.x != right.x;        }    }    Point p1 = new Point(1, 2, 3);    Point p2 = p1;    p1.y = 100;    Console.WriteLine(p1 == p2);//返回true    Console.WriteLine(p1.Equals(p2)); // 返回true    Console.WriteLine(p1.Equals((object)p2)); // 返回true

3.2.2.2、结论：此时程序执行我们重写的Equal函数 and 运算符’==’。

3.2.3、结构体(只有值类型，不重写Equal函数 and 运算符’==’)

3.2.3.1、测试代码：

    struct Point    {        public double x;        public double y;        public double z;        public Point(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }    }    Point p1 = new Point(1, 2, 3);    Point p2 = p1;    Console.WriteLine(p1 == p2);//编译错误：运算符"=="无法应用于"Point"和"Point"类型的操作数    Console.WriteLine(p1.Equals(p2)); // 返回true    Console.WriteLine(p1.Equals((object)p2)); // 返回true    p1.y = 100;    Console.WriteLine(p1.Equals(p2)); // 返回false    Console.WriteLine(p1.Equals((object)p2)); // 返回false

3.2.3.2、程序执行时，CanCompareBits(this)返回true，代码执行return FastEqualsCheck(thisObj, obj);

3.2.3.3、结论：程序判断struct里面所有字段的值，如果全部相等，返回true；否则，返回false。

3.2.4、复杂结构体(有值类型、引用类型，重写Equal函数 and 运算符’==’)

3.2.4.1、测试代码：

    public struct ValPoint    {        public double x;        public double y;        public double z;        public ValPoint(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }        public static bool operator ==(ValPoint left, ValPoint right)        {            return left.x == right.x;        }        public static bool operator !=(ValPoint left, ValPoint right)        {            return left.x != right.x;        }    }    public class RefPoint    {        public double x;        public double y;        public double z;        public RefPoint(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }    }    public struct ValLine    {        public ValPoint vPoint;       // 值类型成员        public RefPoint rPoint;       // 引用类型成员        public ValLine(ValPoint vPoint, RefPoint rPoint)        {            this.vPoint = vPoint;            this.rPoint = rPoint;        }        public override bool Equals(Object obj)        {            if (!(obj is ValLine))            {                return false;            }            if (((ValLine)obj).vPoint == this.vPoint)            {                return true;            }            return false;        }        public bool Equals(ValLine obj)        {            if (obj.vPoint == this.vPoint)            {                return true;            }            return false;        }        public static bool operator ==(ValLine left, ValLine right)        {            return left.vPoint == right.vPoint;        }        public static bool operator !=(ValLine left, ValLine right)        {            return left.vPoint != right.vPoint;        }    }    ValPoint vPoint = new ValPoint(1, 2, 3);    ValPoint vPoint2 = new ValPoint(1, 2, 3);    ValPoint vPoint3 = new ValPoint(10, 20, 30);    RefPoint rPoint = new RefPoint(4, 5, 6);    RefPoint rPoint2 = new RefPoint(7, 8, 9);    ValLine p1 = new ValLine(vPoint, rPoint);    ValLine p2 = p1;    p2.vPoint = vPoint2;    Console.WriteLine(p1 == p2); //返回true    Console.WriteLine(p1.Equals(p2)); //返回true    Console.WriteLine(p1.Equals((object)p2)); //返回true    p2 = p1;    p2.vPoint = vPoint3;    Console.WriteLine(p1 == p2); //返回true    Console.WriteLine(p1.Equals(p2)); //返回false    Console.WriteLine(p1.Equals((object)p2)); //返回false    p2 = p1;    p2.rPoint = rPoint2;    Console.WriteLine(p1 == p2); //返回true    Console.WriteLine(p1.Equals(p2)); //返回true    Console.WriteLine(p1.Equals((object)p2)); //返回true

3.2.4.2、结论：此时程序执行我们重写的Equal函数 and 运算符’==’。

3.2.5、复杂结构体(内部值类型、引用类型，不重写Equal函数 and 运算符’==’)

3.2.5.1、测试代码：

    public struct ValPoint    {        public double x;        public double y;        public double z;        public ValPoint(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }    }    public class RefPoint    {        public double x;        public double y;        public double z;        public RefPoint(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }    }    public struct ValLine    {        public ValPoint vPoint;       // 值类型成员        public RefPoint rPoint;       // 引用类型成员        public ValLine(ValPoint vPoint, RefPoint rPoint)        {            this.vPoint = vPoint;            this.rPoint = rPoint;        }    }    ValPoint vPoint = new ValPoint(1, 2, 3);    ValPoint vPoint2 = new ValPoint(1, 2, 3);    ValPoint vPoint3 = new ValPoint(10, 20, 30);    RefPoint rPoint = new RefPoint(4, 5, 6);    RefPoint rPoint2 = new RefPoint(7, 8, 9);    ValLine p1 = new ValLine(vPoint, rPoint);    ValLine p2 = p1;    Console.WriteLine(p1 == p2);//编译错误：运算符"=="无法应用于"Point"和"Point"类型的操作数    p2.vPoint = vPoint2;    Console.WriteLine(p1.Equals(p2)); //返回true    Console.WriteLine(p1.Equals((object)p2)); //返回true    p2 = p1;    p2.vPoint = vPoint3;    Console.WriteLine(p1.Equals(p2)); //返回false    Console.WriteLine(p1.Equals((object)p2)); //返回false    p2 = p1;    p2.rPoint = rPoint2;    Console.WriteLine(p1.Equals(p2)); //返回false    Console.WriteLine(p1.Equals((object)p2)); //返回false

3.2.5.2、程序执行时，CanCompareBits(this)返回false，代码执行ValueType类Equal函数的下面语句

                FieldInfo[] thisFields = thisType.GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);                for (int i=0; i<thisFields.Length; i++) {                    thisResult = ((RtFieldInfo)thisFields[i]).UnsafeGetValue(thisObj);                    thatResult = ((RtFieldInfo)thisFields[i]).UnsafeGetValue(obj);                    if (thisResult == null) {                        if (thatResult != null)                            return false;                    }                    else                    if (!thisResult.Equals(thatResult)) {                        return false;                    }                }                return true;

3.2.5.3、结论：程序判断struct里面所有字段,值类型就判断值是否相等；引用类型就判断是否引用相等。

4、引用类型Equal函数 and 运算符’==’

4.1、字符串string

4.1.1、C#语言规范5.0中文版中的字符串相等运算符介绍

4.1.2、string的Equal函数和’==’重载运算符函数代码

        String        {            // Determines whether two strings match.            [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]            public override bool Equals(Object obj) {                if (this == null)                        //this is necessary to guard against reverse-pinvokes and                    throw new NullReferenceException();  //other callers who do not use the callvirt instruction                String str = obj as String;                if (str == null)                    return false;                if (Object.ReferenceEquals(this, obj))                    return true;                if (this.Length != str.Length)                    return false;                return EqualsHelper(this, str);            }            // Determines whether two strings match.            [Pure]            [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]            public bool Equals(String value) {                if (this == null)                        //this is necessary to guard against reverse-pinvokes and                    throw new NullReferenceException();  //other callers who do not use the callvirt instruction                if (value == null)                    return false;                if (Object.ReferenceEquals(this, value))                    return true;                if (this.Length != value.Length)                    return false;                return EqualsHelper(this, value);            }            public static bool operator == (String a, String b) {               return String.Equals(a, b);            }            // Determines whether two Strings match.            [Pure]            public static bool Equals(String a, String b) {                if ((Object)a==(Object)b) {                    return true;                }                if ((Object)a==null || (Object)b==null) {                    return false;                }                if (a.Length != b.Length)                    return false;                return EqualsHelper(a, b);            }            [System.Security.SecuritySafeCritical]  // auto-generated            [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]            private unsafe static bool EqualsHelper(String strA, String strB)            {                Contract.Requires(strA != null);                Contract.Requires(strB != null);                Contract.Requires(strA.Length == strB.Length);                int length = strA.Length;                fixed (char* ap = &strA.m_firstChar) fixed (char* bp = &strB.m_firstChar)                {                    char* a = ap;                    char* b = bp;                    // unroll the loop    #if AMD64                    // for AMD64 bit platform we unroll by 12 and                    // check 3 qword at a time. This is less code                    // than the 32 bit case and is shorter                    // pathlength                    while (length >= 12)                    {                        if (*(long*)a     != *(long*)b) return false;                        if (*(long*)(a+4) != *(long*)(b+4)) return false;                        if (*(long*)(a+8) != *(long*)(b+8)) return false;                        a += 12; b += 12; length -= 12;                    }    #else                    while (length >= 10)                    {                        if (*(int*)a != *(int*)b) return false;                        if (*(int*)(a+2) != *(int*)(b+2)) return false;                        if (*(int*)(a+4) != *(int*)(b+4)) return false;                        if (*(int*)(a+6) != *(int*)(b+6)) return false;                        if (*(int*)(a+8) != *(int*)(b+8)) return false;                        a += 10; b += 10; length -= 10;                    }    #endif                    // This depends on the fact that the String objects are                    // always zero terminated and that the terminating zero is not included                    // in the length. For odd string sizes, the last compare will include                    // the zero terminator.                    while (length > 0)                     {                        if (*(int*)a != *(int*)b) break;                        a += 2; b += 2; length -= 2;                    }                    return (length <= 0);                }            }                   }

4.1.3、Object.ReferenceEquals(this, value)如果this、value是同一个引用，返回true；否则，返回false。

            {                string a = "a1!";                string b = "a1!";                Console.WriteLine(Object.ReferenceEquals(a, b));//返回true,可以判断编译器将a与b所指向的"a1!"优化成一个地方。            }            {                string a = "Test";                string b = string.Copy(a);                Console.WriteLine(Object.ReferenceEquals(a, b));//返回false            }            {                string a = "Test";                string b = (string)a.Clone();                Console.WriteLine(Object.ReferenceEquals(a, b));//返回true            }            {                char[] ch = new char[] { 'a', 'A', '@' };                string a = "aA@";                string b = new string(ch);                Console.WriteLine(Object.ReferenceEquals(a, b));//返回false            }

4.1.4、学习EqualsHelper(String strA, String strB)函数之前，我们先看一段代码

            unsafe            {                char[] firstCharA = "abc".ToCharArray();                int length = firstCharA.Length;                fixed (char* ap = firstCharA)                {                    for (int i = 0; i < length; i++)                    {                        Console.WriteLine(*(char*)(ap + i));                    }                }            }            unsafe            {                int[] firstCharA = new int[] { 1, 20, 300 };                int length = firstCharA.Length;                fixed (int* ap = firstCharA)                {                    for (int i = 0; i < length; i++)                    {                        Console.WriteLine(*(int*)(ap + i));                    }                }            }            

4.1.5、修改后EqualsHelper(String strA, String strB)函数

        private unsafe static bool EqualsHelper(String strA, String strB)        {            Contract.Requires(strA != null);            Contract.Requires(strB != null);            Contract.Requires(strA.Length == strB.Length);            int length = strA.Length;            char[] firstCharA = strA.ToCharArray();            char[] firstCharB = strB.ToCharArray();            fixed (char* ap = &firstCharA[0]) fixed (char* bp = &firstCharB[0])//因无法使用m_firstChar，此处是我自行修改。ps：个人认为m_firstChar是指字符串的第一字符，但是无法证明。            //fixed (char* ap = &strA.m_firstChar) fixed (char* bp = &strB.m_firstChar)            {                char* a = ap;                char* b = bp;                while (length >= 10)                {                    if (*(int*)a != *(int*)b) return false;                    if (*(int*)(a + 2) != *(int*)(b + 2)) return false;                    if (*(int*)(a + 4) != *(int*)(b + 4)) return false;                    if (*(int*)(a + 6) != *(int*)(b + 6)) return false;                    if (*(int*)(a + 8) != *(int*)(b + 8)) return false;                    a += 10; b += 10; length -= 10;                }                // This depends on the fact that the String objects are                // always zero terminated and that the terminating zero is not included                // in the length. For odd string sizes, the last compare will include                // the zero terminator.                while (length > 0)                {                    if (*(int*)a != *(int*)b) break;                    a += 2; b += 2; length -= 2;                }                return (length <= 0);            }        }

4.1.6、修改说明

1、fixed (char* ap = &strA.m_firstChar) fixed (char* bp = &strB.m_firstChar)-> fixed (char* ap = &firstCharA[0]) fixed (char* bp = &firstCharB[0])2、(*(int*)a->获取的数据是两个char值（低位ASCII*65536+高位ASCII）[低位在前，高位在后]。 [char两个字节,范围U+0000到U+FFFF]3、(*(char*)a->获取的数据是一个char值[见上面测试例子]

4.1.7、测试EqualsHelper(String strA, String strB)函数

            {                string a = "abcd";                string b = "abcd";                Console.WriteLine(EqualsHelper(a,b));//返回true            }            {                string a = "Test";                string b = string.Copy(a);                Console.WriteLine(EqualsHelper(a, b));//返回true            }            {                string a = "Test";                string b = (string)a.Clone();                Console.WriteLine(EqualsHelper(a, b));//返回true            }            {                char[] ch = new char[] { 'a', 'A', '@' };                string a = "aA@";                string b = new string(ch);                Console.WriteLine(EqualsHelper(a, b));//返回true            }

4.1.8、结论：string类型 a == b、string.Equals(a, b)、a.Equals(b)、a.Equals((object)b)，如果 a 的值与 b 的值相同，则为 true；否则为 false。

4.2、类class

4.2.1、C#语言规范5.0中文版中的引用类型相等运算符介绍

4.2.2、Object内部的Equals函数

        Object        {            public virtual bool Equals(Object obj)            {                return RuntimeHelpers.Equals(this, obj);//无法查到详细代码            }            public static bool Equals(Object objA, Object objB)             {                if (objA==objB) {                    return true;                }                if (objA==null || objB==null) {                    return false;                }                return objA.Equals(objB);            }            [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]            [System.Runtime.Versioning.NonVersionable]            public static bool ReferenceEquals (Object objA, Object objB) {                return objA == objB;            }        } 

4.2.3、类(不重写Equal函数 and 运算符’==’)

    public class RefPoint    {        public double x;        public double y;        public double z;        public RefPoint(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }    }            RefPoint p1 = new RefPoint(4, 5, 6);            RefPoint p2 = p1;            Console.WriteLine(p1.Equals(p2));//返回true            Console.WriteLine(object.Equals(p1, p2));//返回true            Console.WriteLine(object.ReferenceEquals(p1, p2));//返回true            Console.WriteLine(p1 == p2);//返回true            p2 = new RefPoint(4, 5, 6);//虽然值一样，但是引用对象不一样            Console.WriteLine(p1.Equals(p2));//返回false            Console.WriteLine(object.Equals(p1, p2));//返回false            Console.WriteLine(object.ReferenceEquals(p1, p2));//返回false            Console.WriteLine(p1 == p2);//返回false

4.2.4、类(重写Equal函数 and 运算符’==’)

    public class RefPoint    {        public double x;        public double y;        public double z;        public RefPoint(double X, double Y, double Z)        {            this.x = X;            this.y = Y;            this.z = Z;        }        public override bool Equals(Object obj)        {            if (!(obj is RefPoint))            {                return false;            }            if (((RefPoint)obj).x == this.x)            {                return true;            }            return false;        }        public bool Equals(RefPoint obj)        {            if (obj.x == this.x)            {                return true;            }            return false;        }        public static bool operator ==(RefPoint left, RefPoint right)        {            return left.x == right.x;        }        public static bool operator !=(RefPoint left, RefPoint right)        {            return left.x != right.x;        }    }            RefPoint p1 = new RefPoint(4, 5, 6);            RefPoint p2 = p1;            Console.WriteLine(p1.Equals(p2));//返回true            Console.WriteLine(object.Equals(p1, p2));//返回true            Console.WriteLine(object.ReferenceEquals(p1, p2));//返回true            Console.WriteLine(p1 == p2);//返回true            p2 = new RefPoint(4, 50, 60);            Console.WriteLine(p1.Equals(p2));//返回true            Console.WriteLine(object.Equals(p1, p2));//返回true            Console.WriteLine(object.ReferenceEquals(p1, p2));//返回false            Console.WriteLine(p1 == p2);//返回true

4.2.5、ReferenceEquals (Object objA, Object objB)返回objA == objB。如果objA、 objB引用同一个对象(只判断是否引用同一个对象，即使我们自行重载了’==’运算符，也没用)，返回true；否则，返回false。

5、总结

先介绍简单值类型，再到结构体，字符串，类。把每个类型Equal和’==’用法做个总结，加深自己记忆的同时，也希望能帮助到你。另：本文只代表本人观点，如果有误，还望告知。

6、参考

6.1、C#类型基础

6.2、 C#语言规范5.0中文版

6.3、Reference Source