关于php正则表达式的两点备注 - 中国WEB开发者网络 (http://www.webasp.net) -- 技术教程 (http://www.webasp.net/article/) --- 关于php正则表达式的两点备注 (http://www.webasp.net/article/14/13342.htm) |
| -- 作者：未知 -- 发布日期： 2004-09-22 |
| severaltipsaboutRegularExpressions
1.processfor"greedy" Bydefault,thequantifiersare"greedy",thatis,they matchasmuchaspossible(uptothemaximumnumberofper- mittedtimes),withoutcausingtherestofthepatternto fail.Theclassicexampleofwherethisgivesproblemsisin tryingtomatchcommentsinCprograms.Theseappearbetween thesequences/*and*/andwithinthesequence,individual *and/charactersmayappear.AnattempttomatchCcom- mentsbyapplyingthepattern /\*.*\*/ tothestring /*firstcommand*/notcomment/*secondcomment*/ fails,becauseitmatchestheentirestringduetothe greedinessofthe.*item. However,ifaquantifierisfollowedbyaquestionmark, thenitceasestobegreedy,andinsteadmatchestheminimum numberoftimespossible,sothepattern /\*.*?\*/ |
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