Index was outside the bounds of the array.

背景今天写了这么一个函数：

private string DateFormatConversion(string str)        {                string year = "";                char[] pstr = str.ToCharArray();                for (int k = 0; k < 4; k++)                {                    year += pstr[k];                }                return year;        }

当str传入值如空的时候，就会提示“Index was outside the bounds of the array.”错误。

解决方案：

在处理str之前，先判断str.Length是否大于零