重学CSharp（一）

       今天，又一次拿起C＃高级编程教材。记得刚开始接触Asp.net的时候，我是什么都看不懂的，说真的我挺感谢带我进入asp.net的那位朋友，他告诉我，其实你不需要知道为什么，刚开始就跟着做就好了，也不用刻意去学C＃语言的，现在听起来也许觉得不对，但刚开始要不是这样也许我就走不下来了。因为在此之前，我仅会一点C语言。
      这让我想起玩游戏，比如说魔兽，刚开始我们是不会去考虑伤害和兵种的，只要能赢就行，但熟悉了以后，就不但想赢，还要赢得漂亮。
      好了，下面来写一些值得自己多注意的地方吧。
      都知道C＃里面有值和引用类型，它们的区别在于存在于堆栈还是堆中，最好的例子还是类和结构的区别。
      下面来看这段代码：
      using System;

      class RefTest
      {
            public int Width;
            public int Height;
      }

      struct ValTest
      {
             public int Width;
             public int Height;
      }

      class Test
      {
         public static void Main()
         {
            RefTest ref = new RefTest();
            ref.Width = 10;
            ref.Height = 20;
            RefTest ref2 = ref;
            Console.WriteLine("ref2 = " + ref2.Width + "x" + ref2.Height );
            ref.Width = 20;
            ref.Height = 30;
            Console.WriteLine("ref2 = " + ref2.Width + "x" + ref2.Height );

            ValTest val = new ValTest();
            val.Width = 10;
            val.Height = 20;
            ValTest val2 = val;
            Console.WriteLine("val2 = " + val2.Width + "x" + val2.Height );
            val.Width = 20;
            val.Height = 30;
            Console.WriteLine("val2 = " + val2.Width + "x" + val2.Height );
         }
      }

         编译后很容易知道结果，值类型的是不会变的，而引用的将改变，也就是说定义类的会改变，结构的不会改变，我刚开始理解起来挺不容易的，但再回头就容易多了，其实再陌生的东西接触多了也会变得熟悉。

         但同样有例外的，比说string就是引用类型，但是下面这段代码大家觉得会是什么呢？
         using System;

         class Test
         {
               public static void Main()
               {
                     string s1 = "a string";
                     string s2 = s1;
                     Console.WriteLine("s2 = " + s2);
                     s1 = "another string";
                     Console.WriteLine("s2 = " + s2);
               }
         }
         第二次输出的会是什么呢？很遗憾，虽然是引用类型，但是在这里它输出的还是  a string。
         再接下来是ref 和out 关键字。
         using System;

         class Test
         {
               static void someFunction(ints[] Ints, int i)
               {
                     Ints[0] = 100;
                     i = 100;
               }
               
               public static void Main()
               {
                     int i = 0;
                     int[] Ints = {0,1,2,3,4};
                     Console.WriteLine("i = " + i);
                     Console.WriteLine("Ints[0] = " + Ints[0]);

                     someFunction(Ints, i)
                      Console.WriteLine("i = " + i);
                     Console.WriteLine("Ints[0] = " + Ints[0]);
               }
         }
         数组是引用类型，而i是值类型，结果很容易想到，但是如果给i加上ref关键字以后呢？

         using System;

         class Test
         {
               static void someFunction(ints[] Ints, ref int i)
               {
                     Ints[0] = 100;
                     i = 100;
               }
               
               public static void Main()
               {
                     int i = 0;
                     int[] Ints = {0,1,2,3,4};
                     Console.WriteLine("i = " + i);
                     Console.WriteLine("Ints[0] = " + Ints[0]);

                     someFunction(Ints, ref i)
                      Console.WriteLine("i = " + i);
                     Console.WriteLine("Ints[0] = " + Ints[0]);
               }
         }
         这里我告诉大家结果，i的值会变成100。因为用了ref关键字，所以对变量做的任何改变都会影响原来对象的值。
         out关键字是

         using System;

         class Test
         {
               static void someFunction(out int i)
               {
                     i = 100;
               }
               
               public static void Main()
               {
                     int i ;//注意，这里对i没有初始化，也不能初始化，否则会报错。
                     someFunction(out i)
                     Console.WriteLine("i = " + i);
               }
         }
         好了，今天先写到这里！

转载于:https://www.cnblogs.com/shahouhou/archive/2007/06/20/790903.html