ref & out

【ref & out - C#中的参数传递】

　　ref与out均指定函数参数按引用传递，惟一的不同是，ref传递的参数必须初始化，而out可以不用。

　　ref与out无法作为重载的依据，即ref与out编译器认为一样。如下：

　　

　　但是ref函数与非ref函数是可以重载的，如下：

　　

　　To use a ref parameter, both the method definition and the calling method must explicitly use the ref keyword, as shown in the following example.

　　

　　A variable of a reference type does not contain its data directly; it contains a reference to its data. When you pass a reference-type parameter by value, it is possible to change the data pointed to by the reference, such as the value of a class member. However, you cannot change the value of the reference itself; that is, you cannot use the same reference to allocate memory for a new class and have it persist outside the block. To do that, pass the parameter using the ref or out keyword.

class PassingRefByVal 
{
    static void Change(int[] pArray)
    {
        pArray[0] = 888;  // This change affects the original element.
        pArray = new int[5] {-3, -1, -2, -3, -4};   // This change is local.
        System.Console.WriteLine("Inside the method, the first element is: {0}", pArray[0]);
    }

    static void Main() 
    {
        int[] arr = {1, 4, 5};
        System.Console.WriteLine("Inside Main, before calling the method, the first element is: {0}", arr [0]);

        Change(arr);
        System.Console.WriteLine("Inside Main, after calling the method, the first element is: {0}", arr [0]);
    }
}
/* Output:
    Inside Main, before calling the method, the first element is: 1
    Inside the method, the first element is: -3
    Inside Main, after calling the method, the first element is: 888
*/

参考：

1、http://msdn.microsoft.com/zh-cn/library/14akc2c7(VS.80).aspx

2、http://msdn.microsoft.com/zh-cn/library/t3c3bfhx(v=vs.80).aspx

3、http://msdn.microsoft.com/zh-cn/library/s6938f28.aspx