C为什么要用StartsWith而不是Substring进行

　　字符串的截取匹配操作在开发中非常常见，比如下面这个示例：我要匹配查找出来字符串数组中以abc开头的字符串并打印，我下面分别用了两种方式实现，代码如下：
　　spanclasscodesnippetouterspanclasscodesnippetkeywordusingspanSystem；spanspanclasscodesnippetouter
　　spanspanclasscodesnippetouterspanclasscodesnippetkeywordnamespacespanspanclasscodesnippettitleConsoleApp23spanspanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetkeywordclassspanspanclasscodesnippettitleProgramspanspanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetfunctionspanclasscodesnippetkeywordstaticspanspanclasscodesnippetkeywordvoidspanspanclasscodesnippettitleMainspan（spanclasscodesnippetparamsspanclasscodesnippetkeywordstringspan〔〕argsspan）spanspanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetkeywordstringspan〔〕strsspanclasscodesnippetkeywordnewspanspanclasscodesnippetkeywordstringspan〔〕｛spanclasscodesnippetstringabc123span，spanclasscodesnippetstringabc456span，spanclasscodesnippetstringab123span，spanclasscodesnippetstringa12345span｝；spanspanclasscodesnippetouter
　　spanspanclasscodesnippetouterspanclasscodesnippetcomment方法1spanspanspanclasscodesnippetouterspanclasscodesnippetkeywordforeachspan（spanclasscodesnippetkeywordvarspanstrspanclasscodesnippetkeywordinspanstrs）spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetkeywordifspan（str。Substring（spanclasscodesnippetnumber0span，spanclasscodesnippetnumber3span）spanclasscodesnippetstringabcspan）spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterConsole。WriteLine（str）；spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter｝spanspanclasscodesnippetouterConsole。WriteLine（）；spanspanclasscodesnippetouter
　　spanspanclasscodesnippetouterspanclasscodesnippetcomment方法2spanspanspanclasscodesnippetouterspanclasscodesnippetkeywordforeachspan（spanclasscodesnippetkeywordvarspanstrspanclasscodesnippetkeywordinspanstrs）spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetkeywordifspan（str。StartsWith（spanclasscodesnippetstringabcspan））spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterConsole。WriteLine（str）；spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter
　　spanspanclasscodesnippetouterConsole。ReadKey（）；spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter
　　span
　　运行结果如下：
　　诚然，两种方法都输出了正确的结果。
　　那么既然，两种方式都能实现，这两种方法有没有什么区别呢？当然有的，而且大多数时候，一个老练的程序员都会用StartsWith而不是Substring，为什么呢？
　　往下看，我把数据源修改下：
　　spanclasscodesnippetouterspanclasscodesnippetfunctionspanclasscodesnippetkeywordstaticspanspanclasscodesnippetkeywordvoidspanspanclasscodesnippettitleMainspan（spanclasscodesnippetparamsspanclasscodesnippetkeywordstringspan〔〕argsspan）spanspanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetkeywordstringspan〔〕strsspanclasscodesnippetkeywordnewspanspanclasscodesnippetkeywordstringspan〔〕｛spanclasscodesnippetstringabc123span，spanclasscodesnippetstringabc456span，spanclasscodesnippetstringab123span，spanclasscodesnippetstringa12345span，spanclasscodesnippetstringabcspan，spanclasscodesnippetstringabspan｝；spanspanclasscodesnippetouter
　　spanspanclasscodesnippetouterspanclasscodesnippetcomment方法1spanspanspanclasscodesnippetouterspanclasscodesnippetkeywordforeachspan（spanclasscodesnippetkeywordvarspanstrspanclasscodesnippetkeywordinspanstrs）spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetkeywordifspan（str。Substring（spanclasscodesnippetnumber0span，spanclasscodesnippetnumber3span）spanclasscodesnippetstringabcspan）spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterConsole。WriteLine（str）；spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter｝spanspanclasscodesnippetouterConsole。WriteLine（）；spanspanclasscodesnippetouter
　　spanspanclasscodesnippetouterspanclasscodesnippetcomment方法2spanspanspanclasscodesnippetouterspanclasscodesnippetkeywordforeachspan（spanclasscodesnippetkeywordvarspanstrspanclasscodesnippetkeywordinspanstrs）spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterspanclasscodesnippetkeywordifspan（str。StartsWith（spanclasscodesnippetstringabcspan））spanspanclasscodesnippetouter｛spanspanclasscodesnippetouterConsole。WriteLine（str）；spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter｝spanspanclasscodesnippetouter
　　spanspanclasscodesnippetouterConsole。ReadKey（）；spanspanclasscodesnippetouter｝span
　　运行后，方法一直接崩了，但是方法2则可以正确运行出来结果
　　看一下Substring的用法解释：startIndex加length指示不在此实例内的位置。或startIndex或length小于零。，所以当字符串小于你要截取的长度时，你如果没用trycatch去捕获异常，代码就崩溃了。
　　spanclasscodesnippetouterspanclasscodesnippetcommentspanspanspanclasscodesnippetouterspanclasscodesnippetcomment摘要：spanspanspanclasscodesnippetouterspanclasscodesnippetcomment从此实例检索子字符串。子字符串从指定的字符位置开始且具有指定的长度。spanspanspanclasscodesnippetouterspanclasscodesnippetcommentspanspanspanclasscodesnippetouterspanclasscodesnippetcomment参数：spanspanspanclasscodesnippetouterspanclasscodesnippetcommentstartIndex：spanspanspanclasscodesnippetouterspanclasscodesnippetcomment此实例中子字符串的起始字符位置（从零开始）。spanspanspanclasscodesnippetouterspanclasscodesnippetcommentspanspanspanclasscodesnippetouterspanclasscodesnippetcommentlength：spanspanspanclasscodesnippetouterspanclasscodesnippetcomment子字符串中的字符数。spanspanspanclasscodesnippetouterspanclasscodesnippetcommentspanspanspanclasscodesnippetouterspanclasscodesnippetcomment返回结果：spanspanspanclasscodesnippetouterspanclasscodesnippetcomment与此实例中在length处开头、长度为startIndex的子字符串等效的一个字符串；如果System。String。Empty等于此实例的长度且spanspanspanclasscodesnippetouterspanclasscodesnippetcommentstartIndex为零，则为length。spanspanspanclasscodesnippetouterspanclasscodesnippetcommentspanspanspanclasscodesnippetouterspanclasscodesnippetcomment异常：spanspanspanclasscodesnippetouterspanclasscodesnippetcommentT：System。ArgumentOutOfRangeException：spanspanspanclasscodesnippetouterspanclasscodesnippetcommentstartIndex加length指示不在此实例内的位置。或startIndex或length小于零。spanspanspanclasscodesnippetouter〔spanclasscodesnippetmetaSecuritySafeCriticalspan〕spanspanclasscodesnippetouterspanclasscodesnippetfunctionspanclasscodesnippetkeywordpublicspanStringspanclasscodesnippettitleSubstringspan（spanclasscodesnippetparamsspanclasscodesnippetkeywordintspanstartIndex，spanclasscodesnippetkeywordintspanlengthspan）span；span
　　所以，我们需要慎用Substring，如果非要用，一定需要进行异常处理。