C# ref，out

static void Main(string[] args)
        {
            int a = 1;
            int b = 2;
            string x = "x";
            string y = "y";

            Console.WriteLine("Main-->a:{0},b:{1}", a, b);
            Console.WriteLine("Main-->x:{0},y:{1}", x, y);

            TestInt(a, b);
            TestString(x, y);

            Console.WriteLine("Main-->a:{0},b:{1}", a, b);
            Console.WriteLine("Main-->x:{0},y:{1}", x, y);

            TestIntRef(ref a, ref b);
            TestStringRef(ref x, ref y);

            Console.WriteLine("Main-->a:{0},b:{1}", a, b);
            Console.WriteLine("Main-->x:{0},y:{1}", x, y);
        }

        public static void TestInt(int a, int b)
        {
            a = 10;
            b = 20;
            Console.WriteLine("TestInt-->a:{0},b:{1}", a, b);
        }

        public static void TestIntRef(ref int a, ref int b)
        {
            a = 100;
            b = 200;
            Console.WriteLine("TestIntRef-->a:{0},b:{1}", a, b);
        }

        public static void TestString(string x, string y)
        {
            x = "123x";
            y = "123y";
            Console.WriteLine("TestString-->x:{0},y:{1}", x, y);
        }

        public static void TestStringRef(ref string x, ref string y)
        {
            x = "ref:123x";
            y = "ref:123y";
            Console.WriteLine("TestStringRef-->x:{0},y:{1}", x, y);
        }

Out：

static void Main(string[] args)
        {
            int a;
            string x, y;
            TestOut(out a);
            Console.WriteLine(a);　　//a等于101s
 }

        public static void TestOut(out int a)
        {
            a = 101;
        }

总结：out 关键字会导致参数通过引用来传递。这与 ref 关键字类似，不同之处在于 ref 要求变量必须在传递之前进行初始化。若要使用 out 参数，方法定义和调用方法都必须显式使用 out 关键字