Greta 正则表达式.docx

Greta 正则表达式.docx

《Greta 正则表达式.docx》由会员分享，可在线阅读，更多相关《Greta 正则表达式.docx（34页珍藏版）》请在冰豆网上搜索。

Greta正则表达式

GRETA:

TheGRETARegularExpressionTemplateArchive

Copyright EricNiebler,2002

ThepurposeofthisdocumentistodescribehowtousetheGRETARegularExpressionTemplateArchive. Itdescribestheobjectsinthelibrary,themethodsdefinedontheobjects,andthewaystousetheobjectsandmethodstoperformregularexpressionpatternmatchingonstringsinC++. Itdoesnotdescriberegularexpressionsyntax. ItisenoughtosaythatthefullPerl5syntaxissupported. IfyouarenotfamiliarwithPerl’sregularexpressionsyntax,IrecommendreadingChapter2of ProgrammingPerl,2nd Ed. （a.k.a.TheCamelBook）,oneofthemanyfinebooksputoutbyO’Reillypublishers. 

GRETA:

 TheGRETARegularExpressionTemplateArchive

Overview

AWordaboutSpeed

NoticetoUsersofVersion1.x

TherpatternObject

rpattern:

:

string_type

rpattern:

:

rpattern

rpattern:

:

match

rpattern:

:

substitute

rpattern:

:

count

rpattern:

:

split

rpattern:

:

set_substitution

rpattern:

:

cgroups

match_results,subst_resultsandsplit_results

match_results:

:

cbackrefs

match_results:

:

backref

match_results:

:

rstart

match_results:

:

rlength

match_results:

:

all_backrefs

subst_results:

:

backref_str

split_results:

:

strings

TheSyntaxModule

register_intrinsic_charset

CustomizingYourSearch

NOCASE

GLOBAL

MULTILINE

SINGLELINE

EXTENDED

RIGHTMOST

NOBACKREFS

ALLBACKREFS

FIRSTBACKREFS

NORMALIZE

MatchingModes

MODE_FAST

MODE_SAFE

MODE_MIXED

KnownIssuesandPerlIncompatibilities

EmbeddedCodeinaRegularExpression

PatternModifierScope

CommentBlocksBeforeQuantifiers

VariableWidthLook-BehindAssertions

RecursivePatterns

Compile-TimeSwitches

REGEX_WIDE_AND_NARROW

REGEX_POSIX

REGEX_NO_PERL

REGEX_DEBUG

REGEX_DEBUG_HEAP

REGEX_STACK_ALIGNMENT

REGEX_FOLD_INSTANTIATIONS

REGEX_TO_INSTANTIATE

Miscellaneous

StaticConstPatterns

Thread-safety

StackUsage

DBCS

STL

VC7andManagedCode

TemplateInstantiation

ContactInformation

Appendix1:

History

Appendix2:

ImplementationDetails

Overview

TheregularexpressiontemplatelibrarycontainsobjectsandfunctionsthatmakeitpossibletoperformpatternmatchingandsubstitutiononstringsinC++. Theyare:

∙rpattern:

thepatterntouseduringthesearch.

∙match_results/subst_results:

containerfortheresultsofamatch/substitution.

Toperformasearchorreplaceoperation,youwilltypicallyfirstinitializean rpattern objectbygivingitastringrepresentingthepatternagainstwhichtomatch. Youwillthencallamethodontherpatternobject（match（） or substitute（）,forinstance）,passingitastringtomatchagainstanda match_results objectstoreceivetheresultsofthematch. Ifthe match（）/substitute（） fails,themethodreturnsfalse. Ifitsucceeds,itreturnstrue,andthe match_results objectstorestheresultingarrayof backreferences internally. （Here,theterm backreference hasthesamemeaningasitdoesinPerl. Backreferencesprovideextrainformationaboutwhatpartsofthepatternmatchedwhichpartsofthestring.） Therearemethodsonthe match_results objecttomakethebackreferenceinformationavailable. Forexample:

#include

#include

#include“regexpr2.h”

usingnamespacestd;

usingnamespaceregex;

intmain（）{

   match_resultsresults;

   stringstr（“Thebookcost$12.34”）;

   rpatternpat（“\\$（\\d+）（\\.（\\d\\d））?

”）; 

    //Matchadollarsignfollowedbyoneormoredigits,

    //optionallyfollowedbyaperiodandtwomoredigits.

    //Thedouble-escapesarenecessarytosatisfythecompiler.

   match_results:

:

backref_typebr=pat.match（str,results）;

   if（br.matched）{

       cout<<“matchsuccess!

”<

       cout<<“price:

”<

   }else{

       cout<<“matchfailed!

”<

   }

   return0;

}

Theaboveprogramwouldprintoutthefollowing:

matchsuccess!

price:

$12.34

Thefollowingsectionsdiscussthe rpattern objectindetailandhowtocustomizeyoursearchestobefasterandmoreefficient.

Note:

alldeclarationsintheheaderfile（regexpr2.h）arecontainedinthe regex namespace. Touseanyoftheobjects,methodsorenumerationsdescribedinthisdocument,youmustprependalldeclarationswith“regex:

:

”oryoumusthavethe“usingnamespaceregex;”directivesomewherewithintheenclosingscopeofyourdeclarations. Forsimplicity,I’veleftoffthe“regex:

:

”prefixesintherestofmycodesnippets.

AWordaboutSpeed

Differentregexenginesaregoodondifferenttypesofpatterns. Thatsaid,Ihavefoundmyregexenginetobeprettyquick. Forabenchmark,Imatchedthepattern“^（[0-9]+）（\-||$）（.*）$”againstthestring“100-thisisalineofftpresponsewhichcontainsamessagestring”. GRETAisabout7timesfasterthantheregexlibraryinboost（http:

//www.boost.org）,andabout10timesfasterthantheregularexpressionclassesinATL7. Forthisinput,GRETAisevenfasterthanPerl,althoughPerlisfasterforsomeotherpatterns. MostregexenginesIhaveseenbuildupanNFA （non-deterministicfinitestateautomaton） andexecuteititeratively,oftenwithabig,slowswitchstatement. Ihaveadifferentapproach:

patternsarecompiledintoadirected,possiblycyclicgraph,andmatchinghappensbytraversingthisgraphrecursively. Inaddition,thecodemakesheavyuseoftemplatestofreezethestateoftheflagsintothecompiledpatternsothattheydon’tneedtobecheckedatmatchtime. Theresultisaprettyleanblobofcodethatcanmatchyourpatternquickly.

Eventhebestalgorithmshavetheirweaknesses,though. MatchingregularexpressionswithbackreferencesisanNP-completeproblem. Therearepatternsthatwillmakeanybacktrackingregexenginetakeexponentialtimetofinish. （Theseusuallyinvolvenestedquantifiers.） Ifyouhaveaperformancecriticalapp,youwouldbesmarttotestyourpatternsforspeed,orprofileyourapptomakesureyouarenotspendingtoomuchtimethrashingaroundintheregexcode. You’vebeenwarned!

Also,seethesection VC7andManagedCode forsomeadviceforcompilingGRETAunderVC7.

NoticetoUsersofVersion1.x

Manythingshavechangedsinceversion1.xoftheRegularExpressionTemplateArchive. Ifyouhavecodewhichusesversion1.x,youwillnotbeabletouseversion2withoutmakingchangestoyourcode. Sorry!

 Therewereanumberofunsafe,unintuitiveinterfacefeaturesofversion1thatIfeltwereworthfixingforversion2. Ifyouneedversion1,IhaveacopyandI’dbehappytogiveittoyou.

Mostnotably,the regexpr objecthasgoneaway. Itwasasubclassof std:

:

string,with match（） and substitute（） methods,anditstoredtheresultsofthematch/substituteinternally. Subclassing std:

:

string isdangerousbecause std:

:

string doesn’thaveavirtualdestructor. Also,matchingisconceptuallyaconstoperation,anditseemedwrongthatitshouldchangeinternalstate.

The match/count/substitute methodshavemovedtothe rpattern object. Thestatethatusedtobestoredinthe regexpr objectisnowputinamatch_results/subst_results container,whichispassedasanoutparametertothe match/substitute methods.

Also,the CSTRINGS flaghasgoneaway. ItisnolongernecessarytooptimizeapatternforusewithC-styleNULL-terminatedstrings. WhenyoupassaC-stylestringtothe rpattern:

:

matchmethod,thesameoptimizationisusedautomatically. （Inearly2.Xversionsofthelibrary,therewasa basic_rpattern_c objectforperformingthisoptimization,butitisnolongernecessaryandhasbeendeprecated.）

Anotherminorchangeinvolvesthe register_intrinsic_charset（） method. Itusedtobeapartof rpattern’sinterface,butithasmovedtothesyntaxmodule.

Despitethesweepinginterfacechanges,themajorityoftheback-endcodeisunchanged. Youshouldexpectpatternsthatworkedinversion1.xtocontinuetoworkinversion2.

TherpatternObject

The rpattern objectcontainstheregularexpressionpatternagainstwhichtomatch. Italsoexposesthe match（）, substitute（）,and count（） methodsyouwillusetoperformregularexpressionmatches. Whenyouinstantiatean rpattern object,thepatternis“compiled”intoastructurethatspeedsuppatternmatching. Oncecompiled,youmayreusethesamepatternformultiplematchoperations.

Hereishow rpattern isdeclared:

template

         typenameSY=perl_syntax

:

iterator_traits:

:

value_type>>

classbasic_rpattern{

…

};

typedefbasic_rpattern

:

basic_string:

:

const_iterator>rpattern;

typedefbasic_rpatternrpattern_c;

The rpattern classisatemplateoniteratortype. Itisalsoatemplateonthesyntaxmodule. Bydefault,thePerlsyntaxmoduleisused,butyouarefreetowriteyourownsyntaxandspecifyitasatemplateparameter. Seethesectiononthe SyntaxModule.

Thefollowingsectionsdescribethemethodsavailableonthe rpattern object.

rpattern:

:

string_type

rpattern:

:

string_type isatypedefthatisusedinmanyofthefollowingfunctionprototypes. Itisdefinedasfollows:

typedefCIconst_iterator;

typedefstd:

:

iterator_traits:

:

value_typechar_type;

typedefstd:

:

basic_stringstring_type;

Thetypedefisalittlecomplicated,butitseffectiswhatyouwouldexpect. Iftheresultofdereferencinga const_iterator isa char,then string_type isthesameas std:

:

string. Ifdereferencinga const_iterator resultsina wchar_t,then string_type isthesameas std:

:

wstring.

rpattern:

:

rpattern

Therearetwoconstructorsforinstantiatingan rpattern object. Herearetheirprototypes:

rpattern:

:

rpattern（

const string_type &pat,

REGEX_FLAGSflags=NOFLAGS,

REGEX_MODEmode=MODE_DEFAULT）; //throw（bad_alloc,bad