什么时候int ++增加？

Question

我有一行代码,

list[index++] = recursiveFunction();

难道index之前或通话后得到递增recursiveFunction？

Answer 1

在函数调用之前执行递增操作.请参阅http://msdn.microsoft.com/en-us/library/aa691322(v=VS.71).aspx.请注意,这与运算符的优先级和关联性无关.

表达式中运算符的求值顺序由运算符的优先级和关联性决定(第7.2.1节).

表达式中的操作数从左到右进行计算.例如,在F(i) + G(i++) * H(i)方法F中使用旧值i调用,然后用旧值i调用方法G,最后,用新值i调用方法H. 这与运算符优先级分开并且与运算符优先级无关.

运算符优先级和关联性仅影响运算符绑定到操作数的方式.这里的问题讨论了操作数评估的副作用.

using System;

class Obj {
   public bool Incremented {get;set;}
   public static Obj operator ++ (Obj o) {
     Console.WriteLine("Increment operator is executed.");
     return new Obj {Incremented = true};
   }
}

class L {
  public int this[Obj o] {
    set { Console.WriteLine("Assignment called with " + 
            (o.Incremented ? "incremented" : "original") + " indexer value."); }
  }

}
class Test{
  static void Main() {
    Obj o = new Obj();
    L l = new L();
    l[o++] = Func();
  }

  static int Func() {
    Console.WriteLine("Function call.");
    return 10;
  }
}

打印:

Increment operator is executed.
Function call.
Assignment called with original indexer value.

此行为在规范中明确指定,并且在任何符合标准的编译器中应该相同.

Answer 2

在Windows上的Visual Studio 2008/.NET Framework 3.5下,索引在 recursiveFunction调用之前会递增.此示例应用程序将"index = 1"打印到控制台.

class Program
{
    private int index = 0;

    private static void Main()
    {
        new Program().TryMe();
    }

    private void TryMe()
    {
        var list = new List<int>();
        list.Add(1);
        list.Add(2);

        list[index++] = ReturnZero();
    }

    private int ReturnZero()
    {
        Console.WriteLine(string.Format("index = {0}", index));
        return 0;
    }
}