c#引用（ref）的用法和应用实例

无论是浅拷贝与深拷贝，C#都将源对象中的所有字段复制到新的对象中。不过，对于值类型字段，引用类型字段以及字符串类型字段的处理，两种拷贝方式存在一定的区别（见下表）。

1. 一般对C#中传值调用和传引用调用的理解

如果传递的参数是基元类型（int，float等）或结构体（struct），那么就是传值调用。
如果传递的参数是类（class）那么就是传引用调用。
如果传递的参数前有ref或者out关键字，那么就是传引用调用。

验证示例的代码如下：

public class ArgsByRefOrValue{public static void Main(string[] args){// 实验1. 传值调用--基元类型int i = 10;Console.WriteLine("before call ChangeByInt: i = " + i.ToString());ChangeByInt(i);Console.WriteLine("after call ChangeByInt: i = " + i.ToString());Console.WriteLine("==============================================");// 实验2. 传值调用--结构体Person_val p_val = new Person_val();p_val.name = "old val name";Console.WriteLine("before call ChangeByStruct: p_val.name = " + p_val.name);ChangeByStruct(p_val);Console.WriteLine("after call ChangeByStruct: p_val.name = " + p_val.name);Console.WriteLine("==============================================");// 实验3. 传引用调用--类Person_ref p_ref = new Person_ref();p_ref.name = "old ref name";Console.WriteLine("before call ChangeByClass: p_ref.name = " + p_ref.name);ChangeByClass(p_ref);Console.WriteLine("after call ChangeByClass: p_ref.name = " + p_ref.name);Console.WriteLine("==============================================");// 实验4. 传引用调用--利用refPerson_ref p = new Person_ref();p.name = "old ref name";Console.WriteLine("before call ChangeByClassRef: p.name = " + p.name);ChangeByClassRef(ref p);Console.WriteLine("after call ChangeByClassRef: p.name = " + p.name);Console.ReadKey(true);}static void ChangeByInt(int i){i = i + 10;Console.WriteLine("when calling ChangeByInt: i = " + i.ToString());}static void ChangeByStruct(Person_val p_val){p_val.name = "new val name";Console.WriteLine("when calling ChangeByStruct: p_val.name = " + p_val.name);}static void ChangeByClass(Person_ref p_ref){p_ref.name = "new ref name";Console.WriteLine("when calling ChangeByClass: p_ref.name = " + p_ref.name);}static void ChangeByClassRef(ref Person_ref p){p.name = "new ref name";Console.WriteLine("when calling ChangeByClassRef: p.name = " + p.name);}}public struct Person_val{public string name;}public class Person_ref{public string name;}

运行结果如下：

看起来似乎上面代码中实验3和实验4是一样的，即对于类（class）来说，不管加不加ref或out，都是传引用调用。

其实，这只是表面的现象，只要稍微改一下代码，结果就不一样了。

修改上面代码，再增加两个实验。

 public class ArgsByRefOrValue{public static void Main(string[] args){// 实验1. 传值调用--基元类型int i = 10;Console.WriteLine("before call ChangeByInt: i = " + i.ToString());ChangeByInt(i);Console.WriteLine("after call ChangeByInt: i = " + i.ToString());Console.WriteLine("==============================================");// 实验2. 传值调用--结构体Person_val p_val = new Person_val();p_val.name = "old val name";Console.WriteLine("before call ChangeByStruct: p_val.name = " + p_val.name);ChangeByStruct(p_val);Console.WriteLine("after call ChangeByStruct: p_val.name = " + p_val.name);Console.WriteLine("==============================================");// 实验3. 传引用调用--类Person_ref p_ref = new Person_ref();p_ref.name = "old ref name";Console.WriteLine("before call ChangeByClass: p_ref.name = " + p_ref.name);ChangeByClass(p_ref);Console.WriteLine("after call ChangeByClass: p_ref.name = " + p_ref.name);Console.WriteLine("==============================================");// 实验4. 传引用调用--利用refPerson_ref p = new Person_ref();p.name = "old ref name";Console.WriteLine("before call ChangeByClassRef: p.name = " + p.name);ChangeByClassRef(ref p);Console.WriteLine("after call ChangeByClassRef: p.name = " + p.name);Console.WriteLine("==============================================");// 实验5. 传引用调用--类 在调用的函数重新new一个对象Person_ref p_ref_new = new Person_ref();p_ref_new.name = "old new ref name";Console.WriteLine("before call ChangeByClassNew: p_ref_new.name = " + p_ref_new.name);ChangeByClassNew(p_ref_new);    //注意区别这里Console.WriteLine("after call ChangeByClassNew: p_ref_new.name = " + p_ref_new.name);Console.WriteLine("==============================================");// 实验6. 传引用调用--利用ref 在调用的函数重新new一个对象Person_ref p_new = new Person_ref();p_new.name = "old new ref name";Console.WriteLine("before call ChangeByClassRefNew: p_new.name = " + p_new.name);ChangeByClassRefNew(ref p_new);Console.WriteLine("after call ChangeByClassRefNew: p_new.name = " + p_new.name);Console.ReadKey(true);}static void ChangeByInt(int i){i = i + 10;Console.WriteLine("when calling ChangeByInt: i = " + i.ToString());}static void ChangeByStruct(Person_val p_val){p_val.name = "new val name";Console.WriteLine("when calling ChangeByStruct: p_val.name = " + p_val.name);}static void ChangeByClass(Person_ref p_ref){p_ref.name = "new ref name";Console.WriteLine("when calling ChangeByClass: p_ref.name = " + p_ref.name);}static void ChangeByClassRef(ref Person_ref p){p.name = "new ref name";Console.WriteLine("when calling ChangeByClassRef: p.name = " + p.name);}static void ChangeByClassNew(Person_ref p_ref_new){p_ref_new = new Person_ref();   //这样不改变 p_ref_newp_ref_newp_ref_new.name = "new ref name";Console.WriteLine("when calling ChangeByClassNew: p_ref_new.name = " + p_ref_new.name);}static void ChangeByClassRefNew(ref Person_ref p_new){p_new = new Person_ref();p_new.name = "new ref name";Console.WriteLine("when calling ChangeByClassRefNew: p_new.name = " + p_new.name);}}public struct Person_val{public string name;}public class Person_ref{public string name;}