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而这个 pageNumber 是经过一个过滤函数输出来的。这个函数的思想大致像这样:
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在这里我想说的是,其实没有必要人为的去引入可能给我们带来大麻烦的 null 这种值。
我们可以先做一个小试验,看看 Request 得到的变量到底有哪几种可能的情况。测试代码如下:
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然后分别测试:
(a) http://localhost/test/typeCheck.asp
(b) http://localhost/test/typeCheck.asp?hello=
(c) http://localhost/test/typeCheck.asp?hello=ok
输出的结果:
(a)
是 Empty
是空字符串
(b)
是空字符串
(c)
有值:#ok#
从上面的输出可以看出,对于默认接收到的值,不管什么情况,我们都可以简单的用 = "" 这个条件来判断是否有值。
而人为的引入 null 是很不可取的做法。(这样做的弊病是跟其他地方可能存在的判断是否合法的标准不兼容,造成混淆)。正确的做法应该默认返回空字符串 ""。
简单一点讲,作为函数的返回值,应该是安全的,有效的值。
在 VBScript 中可以输出 "" 作为安全的返回值。
在 C# 中,要区分值类型和引用类型来处理。
对于值类型可输出一个默认值比如对应于整数输出 0,
而引用类型输出 null 才是合理的。(表示空指针,空引用)。
还可以试试这段代码的输出结果是什么(这个没多少实际意义):
![](/Images/OutliningIndicators/None.gif)
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