翻译文献-扩展c api 技术

外文原文THEEXTENSIONCAPITHISCHAPTERISABOUTTEACHINGSQLITENEWTRICKSTHEPREVIOUSCHAPTERDEALTWITHGENERICDATABASEWORKTHISCHAPTERISABOUTBEINGCREATIVETHELATTERHALFOFTHEAPITHEEXTENSIONAPIOFFERSTHREEBASICWAYSTOEXTENDORCUSTOMIZESQLITE,THROUGHTHECREATIONOFUSERDEFINEDFUNCTIONS,AGGREGATES,ANDCOLLATIONSEQUENCESUSERDEFINEDFUNCTIONSARESQLFUNCTIONSTHATMAPTOSOMEIMPLEMENTATIONTHATYOUWRITETHEYARECALLABLEFROMWITHINSQLFOREXAMPLE,YOUCOULDCREATEAFUNCTIONHELLO_NEWMANTHATRETURNSTHESTRINGHELLOJERRYAND,ONCEITISREGISTERED,CALLITFROMSQLASFOLLOWSSQLITESELECTHELLO_NEWMANASREPLYREPLYHELLOJERRYTHISISASPECIALVERSIONOFTHESQLITECOMMANDLINEPROGRAMICUSTOMIZEDMYSELFTHATINCLUDESHELLO_NEWMANWHENIGETBORED,ICALLITOCCASIONALLYAGGREGATESAREASPECIALFORMOFFUNCTIONANDWORKINMUCHTHESAMEWAYEXCEPTTHATTHEYOPERATEONSETSOFRECORDSANDRETURNAGGREGATEDVALUESOREXPRESSIONSCOMPUTEDOVERAPARTICULARCOLUMNINTHESETORTHEYMAYBECOMPUTEDFROMMULTIPLECOLUMNSSTANDARDAGGREGATESTHATAREBUILTINTOSQLITEINCLUDESUM,COUNT,ANDAVG,FOREXAMPLECOLLATIONSAREMETHODSOFCOMPARINGANDSORTINGTEXTTHATIS,GIVENTWOSTRINGS,ACOLLATIONWOULDDECIDEWHICHONEISGREATER,ORWHETHERTHETWOAREEQUALTHEDEFAULTCOLLATIONINSQLITEISBINARYITCOMPARESSTRINGSBYTEBYBYTEUSINGMEMCMPWHILETHISCOLLATIONHAPPENSTOWORKWELLFORWORDSINTHEENGLISHLANGUAGEANDOTHERLANGUAGESTHATUSEUTF8ENCODING,ITDOESNTNECESSARILYWORKSOWELLFOROTHERLANGUAGESTHATUSEDIFFERENTENCODINGSTHISISWHYSQLITEVERSION3INTRODUCEDUSERDEFINEDCOLLATIONSTHISCHAPTERCOVERSEACHOFTHESETHREEUSERDEFINEDEXTENSIONFACILITIESANDTHEIRASSOCIATEDAPIFUNCTIONSASYOUWILLSEE,WHENCOMBINEDWITHOTHERFACILITIESSUCHASTRIGGERSANDCONFLICTRESOLUTION,THEUSERDEFINEDEXTENSIONSAPICANPROVETOBEAPOWERFULTOOLFORCREATINGNONTRIVIALFEATURESTHATEXTENDSQLITEALLOFTHECODEINTHISCHAPTERISINCLUDEDINEXAMPLESTHATYOUCANOBTAINONLINEFROMTHEAPRESSWEBSITEWWWAPRESSCOMTHEEXAMPLESFORTHISPARTICULARCHAPTERARELOCATEDINTHECH7SUBDIRECTORYOFTHEEXAMPLESFOLDERIWILLSPECIFICALLYPOINTOUTALLTHESOURCEFILESCORRESPONDINGTOTHEEXAMPLESASTHEYAREINTRODUCEDINTHETEXTSOMEOFTHEERRORCHECKINGCODEINTHEFIGURESHASBEENTAKENOUTFORTHESAKEOFCLARITYALSO,MANYEXAMPLESINTHISCHAPTERUSESIMPLECONVENIENCEFUNCTIONSFROMACOMMONLIBRARYIWROTETHATHELPSSIMPLIFYTHEEXAMPLESIWILLPOINTOUTTHESEFUNCTIONSANDEXPLAINWHATTHEYDOASTHEYAREINTRODUCEDINTHETEXTTHECOMMONCODEISLOCATEDINTHECOMMONSUBDIRECTORYOFTHEEXAMPLESFOLDER,ANDMUSTFIRSTBEBUILTBEFORETHEEXAMPLESAREBUILTPLEASEREFERTOTHEREADMEFILEINTHEEXAMPLESFOLDERFORDETAILSONBUILDINGTHECOMMONLIBRARYFINALLY,TOCLEARUPANYCONFUSION,THETERMSSTORAGECLASSANDDATATYPEAREINTERCHANGEABLEYOUKNOWTHATSQLITESTORESDATAINTERNALLYUSINGFIVEDIFFERENTDATATYPES,ORSTORAGECLASSESTHESECLASSESAREINTEGER,FLOAT,TEXT,BLOB,ANDNULL,ASDESCRIBEDINCHAPTER4THROUGHOUTTHECHAPTER,ITRYTOUSETHETERMTHATBESTFITSTHECONTEXTWHENSPEAKINGGENERALLY,IUSETHETERMDATATYPE,ASITSEEMSTHEMOSTAPPROPRIATEWHENSPEAKINGABOUTHOWSQLITEHANDLESASPECIFICVALUEINTERNALLY,IFINDTHATTHETERMSTORAGECLASSSEEMSTOWORKBETTERINEITHERCASE,YOUCANEQUATEEITHERTERMASDESCRIBINGASPECIFICFORMORREPRESENTATIONOFDATATHEAPITHEBASICMETHODFORIMPLEMENTINGFUNCTIONS,AGGREGATES,ANDCOLLATIONSCONSISTSOFIMPLEMENTINGACALLBACKFUNCTIONANDTHENREGISTERINGITINYOURPROGRAMONCEREGISTERED,THEYCANBEUSEDFROMSQLFUNCTIONSANDAGGREGATESUSETHESAMEREGISTRATIONFUNCTIONANDSIMILARCALLBACKFUNCTIONSCOLLATIONSEQUENCES,WHILEUSINGASEPARATEREGISTRATIONFUNCTION,AREALMOSTIDENTICALANDCANBETHOUGHTOFASAPARTICULARCLASSOFUSERDEFINEDFUNCTIONTHELIFETIMEOFUSERDEFINEDAGGREGATES,FUNCTIONS,ANDCOLLATIONSISTRANSIENTTHEYAREREGISTEREDONACONNECTIONBYCONNECTIONBASISTHEYARENOTSTOREDINTHEDATABASEITISUPTOYOUTOENSURETHATYOURAPPLICATIONLOADSYOURCUSTOMEXTENSIONSANDREGISTERSTHEMONEACHCONNECTIONSOMETIMESYOUMAYFINDYOURSELFTHINKINGOFYOUREXTENSIONSINTERMSOFSTOREDPROCEDURESANDCOMPLETELYFORGETABOUTTHEFACTTHATTHEYDONTACTUALLYRESIDEINTHEDATABASEEXTENSIONSEXISTINLIBRARIES,NOTINDATABASES,ANDARERESTRICTEDTOTHELIFEOFYOURPROGRAMIFYOUDONTGRASPTHISCONCEPT,YOUMAYDOSOMETHINGLIKETRYTOCREATEATRIGGERWHICHISSTOREDINTHEDATABASETHATREFERENCESYOUREXTENSIONSWHICHARENTSTOREDINTHEDATABASEANDTHENTURNAROUNDANDTRYTOCALLITFROMTHESQLITESHELLORFROMANAPPLICATIONTHATKNOWSNOTHINGOFYOUREXTENSIONSINTHISCASE,YOUWILLFINDTHATEITHERITTRIGGERSANERRORORNOTHINGHAPPENSEXTENSIONSREQUIREYOURPROGRAMTOREGISTERTHEMONEACHANDEVERYCONNECTIONOTHERWISE,THATCONNECTIONSSQLSYNTAXWILLKNOWNOTHINGABOUTTHEMREGISTERINGFUNCTIONSTHATSAID,YOUCANREGISTERFUNCTIONSANDAGGREGATESONACONNECTIONUSINGTHESQLITE3_CREATE_FUNCTION,WHICHISDECLAREDASFOLLOWSINTSQLITE3_CREATE_FUNCTIONSQLITE3CNX,/CONNECTIONHANDLE/CONSTCHARZFUNCTIONNAME,/FUNCTION/AGGREGATENAMEINSQL/INTNARG,/NUMBEROFARGUMENTS1UNLIMITED/INTETEXTREP,/ENCODINGUTF8,16,ETC/VOIDPUSERDATA,/APPLICATIONDATA,PASSEDTOCALLBACK/VOIDXFUNCSQLITE3_CONTEXT,INT,SQLITE3_VALUE,VOIDXSTEPSQLITE3_CONTEXT,INT,SQLITE3_VALUE,VOIDXFINALSQLITE3_CONTEXTINTSQLITE3_CREATE_FUNCTION16SQLITE3CNX,CONSTVOIDZFUNCTIONNAME,INTNARG,INTETEXTREP,VOIDPUSERDATA,VOIDXFUNCSQLITE3_CONTEXT,INTARGS,SQLITE3_VALUE,VOIDXSTEPSQLITE3_CONTEXT,INTARGS,SQLITE3_VALUE,VOIDXFINALSQLITE3_CONTEXTASINTHEPREVIOUSCHAPTER,IHAVEINCLUDEDBOTHTHEUTF8ANDUTF16VERSIONSOFTHISFUNCTIONTOUNDERSCORETHEFACTTHATTHESQLITEAPIHASFUNCTIONSTHATSUPPORTBOTHENCODINGSHOWEVER,FROMNOWON,IWILLONLYREFERTOTHEUTF8VERSIONSFORTHESAKEOFBREVITYTHEARGUMENTSFORSQLITE3_CREATE_FUNCTIONAREDEFINEDASFOLLOWSCNXTHECONNECTIONHANDLEFUNCTIONSANDAGGREGATESARECONNECTIONSPECIFICTHEYMUSTBEREGISTEREDONTHECONNECTIONASITISOPENEDINORDERTOBEUSEDZFUNCTIONNAMETHEFUNCTIONNAMEASITWILLBECALLEDINSQLNARGTHENUMBEROFARGUMENTSREQUIREDBYTHEFUNCTIONSQLITEWILLENFORCETHISASTHEEXACTNUMBEROFARGUMENTSTHATMUSTBEPROVIDEDTOTHEFUNCTIONHOWEVER,IFYOUSPECIFY1FORTHISVALUE,SQLITEWILLALLOWAVARIABLENUMBEROFARGUMENTSETEXTREPTHEENCODINGALLOWABLEVALUESARESQLITE_UTF8,SQLITE_UTF16,SQLITE_UTF16BE,SQLITE_UTF16LE,ANDSQLITE_ANYSQLITE_ANYISFORASINGLEFUNCTIONIMPLEMENTATIONTHATCANNEGOTIATEANYKINDOFTEXTREPRESENTATIONPROVIDEDPUSERDATAAPPLICATIONSPECIFICDATATHISDATAISMADEAVAILABLETHROUGHTHECALLBACKFUNCTIONSSPECIFIEDINXFUNC,XSTEP,ANDXFINALUNLIKEOTHERFUNCTIONS,WHICHRECEIVETHEDATAASAVOIDPOINTERINTHEARGUMENTLIST,THESEFUNCTIONSMUSTUSEASPECIALAPIFUNCTIONTOOBTAINTHISDATAXFUNCTHEFUNCTIONCALLBACKTHISISTHEACTUALIMPLEMENTATIONOFTHESQLFUNCTIONFUNCTIONSONLYPROVIDETHISCALLBACKANDLEAVETHEXSTEPANDXFINALFUNCTIONPOINTERSNULLTHESELATTERTWOCALLBACKSAREEXCLUSIVELYFORAGGREGATEIMPLEMENTATIONSXSTEPTHEAGGREGATESTEPFUNCTIONEACHTIMESQLITEPROCESSESAROWINANAGGREGATEDRESULTSET,ITCALLSXSTEPTOALLOWTHEAGGREGATETOPROCESSTHERELEVANTFIELDVALUESOFTHATROWANDINCLUDETHERESULTINITSAGGREGATECOMPUTATIONXFINALTHEAGGREGATEFINALIZEFUNCTIONWHENALLROWSHAVEBEENPROCESSED,SQLITECALLSTHISFUNCTIONTOALLOWTHEAGGREGATETOCONCLUDEITSPROCESSING,WHICHUSUALLYCONSISTSOFCOMPUTINGTHEFINALVALUEANDOPTIONALLYCLEANINGUPWITHREGARDTOENCODING,YOUCANREGISTERMULTIPLEVERSIONSOFTHESAMEFUNCTIONDIFFERINGONLYINTHEENCODINGETEXTREPARGUMENTANDSQLITEWILLAUTOMATICALLYSELECTTHEBESTVERSIONOFTHEFUNCTIONFORTHECASEINHANDTHESTEPFUNCTIONTHEFUNCTIONANDAGGREGATESTEPFUNCTIONSAREIDENTICAL,ANDAREDECLAREDASVOIDFNSQLITE3_CONTEXTCTX,INTNARGS,SQLITE3_VALUEVALUESTHECTXARGUMENTISTHEFUNCTION/AGGREGATECONTEXTITHOLDSSTATEFORAPARTICULARFUNCTIONCALLINSTANCEANDISTHEMEANSTHROUGHWHICHYOUOBTAINTHEAPPLICATIONDATAPUSERDATAARGUMENTPROVIDEDINSQLITE3_CREATE_FUNCTIONTHEUSERDATAISOBTAINEDFROMTHECONTEXTUSINGSQLITE3_USER_DATA,WHICHISDECLAREDASFOLLOWSVOIDSQLITE3_USER_DATASQLITE3_CONTEXTFORFUNCTIONS,THISDATAISSHAREDAMONGALLCALLSTOLIKEFUNCTIONS,SOITISNOTREALLYUNIQUETOAPARTICULARINSTANCEOFFUNCTIONCALLTHATIS,THESAMEPUSERDATAISPASSEDORSHAREDAMONGALLINSTANCESOFAGIVENFUNCTIONAGGREGATES,HOWEVER,CANALLOCATETHEIROWNSTATEFOREACHPARTICULARINSTANCEUSINGSQLITE3_AGGREGATE_CONTEXT,DECLAREDASFOLLOWSVOIDSQLITE3_AGGREGATE_CONTEXTSQLITE3_CONTEXT,INTNBYTESTHEFIRSTTIMETHISROUTINEISCALLEDFORAPARTICULARAGGREGATE,ACHUNKOFMEMORYOFSIZENBYTESISALLOCATED,ZEROED,ANDASSOCIATEDWITHTHATCONTEXTONSUBSEQUENTCALLSWITHTHESAMECONTEXTFORTHESAMEAGGREGATEINSTANCE,THISALLOCATEDMEMORYISRETURNEDUSINGTHIS,AGGREGATESHAVEAWAYTOSTORESTATEINBETWEENCALLSINORDERTOACCUMULATEDATAWHENTHEAGGREGATECOMPLETESTHEFINALCALLBACK,THEMEMORYISAUTOMATICALLYFREEDBYSQLITENOTEONEOFTHETHINGSYOUWILLSEETHROUGHOUTTHEAPIISTHEUSEOFUSERDATAINVOIDPOINTERSSINCEMANYPARTSOFTHEAPIINVOLVECALLBACKFUNCTIONS,THESESIMPLYSERVEASACONVENIENCETOHELPYOUMAINTAINSTATEWHENIMPLEMENTINGSAIDCALLBACKFUNCTIONSTHENARGSARGUMENTOFTHECALLBACKFUNCTIONCONTAINSTHENUMBEROFARGUMENTSPASSEDTOTHEFUNCTIONRETURNVALUESTHEVALUESARGUMENTISANARRAYOFSQLITEVALUESTRUCTURESTHATAREHANDLESTOTHEACTUALARGUMENTVALUESTHEACTUALDATAFORTHESEVALUESISOBTAINEDUSINGTHEFAMILYOFSQLITE3_VALUE_XXXFUNCTIONS,WHICHHAVETHEFOLLOWINGFORMXXXSQLITE3_VALUE_XXXSQLITE3_VALUEVALUEWHEREXXXISTHECDATATYPETOBERETURNEDFROMTHEVALUEARGUMENTIFYOUREADCHAPTER6,YOUMAYBETHINKINGTHATTHESEFUNCTIONSHAVEASTRIKINGRESEMBLANCETOTHESQLITE3_COLUMN_XXXFAMILYOFFUNCTIONSANDYOUDBERIGHTTHEYWORKINEXACTLYTHESAMEWAY,EVENDOWNTOTHEDIFFERENCEBETWEENTHEWAYSCALARANDARRAYVALUESAREOBTAINEDTHEFUNCTIONSFOROBTAININGSCALARVALUESAREASFOLLOWSINTSQLITE3_VALUE_INTSQLITE3_VALUELONGLONGINTSQLITE3_VALUE_INT64SQLITE3_VALUEDOUBLESQLITE3_VALUE_DOUBLESQLITE3_VALUETHEFUNCTIONSUSEDTOOBTAINARRAYVALUESAREASFOLLOWSINTSQLITE3_VALUE_BYTESSQLITE3_VALUECONSTVOIDSQLITE3_VALUE_BLOBSQLITE3_VALUECONSTUNSIGNEDCHARSQLITE3_VALUE_TEXTSQLITE3_VALUETHESQLITE3_VALUE_BYTESFUNCTIONRETURNSTHEAMOUNTOFDATAINTHEVALUEBUFFERFORABLOBTHESQLITE3_VALUE_BLOBFUNCTIONRETURNSAPOINTERTOTHATDATAUSINGTHESIZEANDTHEPOINTER,YOUCANTHENCOPYOUTTHEDATAFOREXAMPLE,IFTHEFIRSTARGUMENTINYOURFUNCTIONWASABLOB,ANDYOUWANTEDTOMAKEACOPY,YOUWOULDDOSOMETHINGLIKETHISINTLENVOIDDATALENSQLITE3_VALUE_BYTESVALUES0DATAMALLOCLENMEMCPYDATA,SQLITE3_VALUE_BLOBVALUES0,LENJUSTASTHESQLITE3_COLUMN_XXXFUNCTIONSHAVESQLITE_COLUMN_TYPETOPROVIDETHECOLUMNTYPES,THESQLITE3_VALUE_XXXFUNCTIONSLIKEWISEHAVESQLITE3_VALUE_TYPE,WHICHWORKSINTHESAMEWAYITISDECLAREDASFOLLOWSINTSQLITE3_VALUE_TYPESQLITE3_VALUETHISFUNCTIONRETURNSONEOFTHEFOLLOWINGVALUES,WHICHCORRESPONDTOSQLITESINTERNAL,STORAGECLASSESDATATYPES,DEFINEDASDEFINESQLITE_INTEGER1DEFINESQLITE_FLOAT2DEFINESQLITE_TEXT3DEFINESQLITE_BLOB4DEFINESQLITE_NULL5THISCOVERSTHEBASICWORKINGSOFTHEFUNCTION/AGGREGATEINTERFACEWECANNOWDIVEINTOSOMEEXAMPLESANDEVENAFEWPRACTICALAPPLICATIONSTHECOLLATIONINTERFACEISSOSIMILARTHATRATHERTHANPREVIEWINGITHERE,WEWILLJUSTADDRESSITINFULLAFTERWECOVERFUNCTIONSANDAGGREGATESFUNCTIONSLETSSTARTWITHATRIVIALEXAMPLE,ONETHATISVERYEASYTOFOLLOWLETSIMPLEMENTHELLO_NEWMAN,BUTWITHASLIGHTTWISTIWANTTOINCLUDEUSINGFUNCTIONARGUMENTSINTHEEXAMPLE,SOHELLO_NEWMANWILLTAKEONEARGUMENTTHENAMEOFTHEPERSONADDRESSINGHIMITWILLTHUSWORKASFOLLOWSSQLITESELECTHELLO_NEWMANJERRYASREPLYREPLYHELLOJERRYSQLITESELECTHELLO_NEWMANKRAMERASREPLYREPLYHELLOKRAMERSQLITESELECTHELLO_NEWMANGEORGEASREPLYREPLYHELLOGEORGETHEBASICPROGRAMTAKENFROMHELLO_NEWMANCISSHOWNINLISTING71SOMEOFTHEERRORCHECKINGCODEHASBEENREMOVEDFORCLARITYLISTING71THEHELLO_NEWMANTESTPROGRAMINTMAININTARGC,CHARARGVINTRCSQLITE3DBSQLITE3_OPEN“TESTDB“,SQLITE3_CREATE_FUNCTIONDB,“HELLO_NEWMAN“,1,SQLITE_UTF8,NULL,HELLO_NEWMAN,NULL,NULL/LOGSQLASITISEXECUTED/LOG_SQLDB,1/CALLFUNCTIONWITHONETEXTARGUMENT/FPRINTFSTDOUT,“CALLINGWITHONEARGUMENTN“PRINT_SQL_RESULTDB,“SELECTHELLO_NEWMANJERRY“/CALLFUNCTIONWITHTWOARGUMENTSTHISWILLFAILASWEREGISTEREDTHEFUNCTIONASTAKINGONLYONEARGUMENT/FPRINTFSTDOUT,“NCALLINGWITHTWOARGUMENTSN“PRINT_SQL_RESULTDB,“SELECTHELLO_NEWMANJERRY,ELAINE“/CALLFUNCTIONWITHNOARGUMENTSTHISWILLFAILTOO/FPRINTFSTDOUT,“NCALLINGWITHNOARGUMENTSN“PRINT_SQL_RESULTDB,“SELECTHELLO_NEWMAN“/DONE/SQLITE3_CLOSEDBRETURN0THISPROGRAMCONNECTSTOTHEDATABASE,REGISTERSTHEFUNCTION,ANDTHENCALLSITTHREETIMESTHECALLBACKFUNCTIONISIMPLEMENTEDASFOLLOWSVOIDHELLO_NEWMANSQLITE3_CONTEXTCTX,INTNARGS,SQLITE3_VALUEVALUESCONSTCHARMSG/GENERATENEWMANSREPLY/MSGSQLITE3_MPRINTF“HELLOS“,SQLITE3_VALUE_TEXTVALUES0/SETTHERETURNVALUEHAVESQLITECLEANUPMSGW/SQLITE_FREE/SQLITE3_RESULT_TEXTCTX,MSG,STRLENMSG,SQLITE3_FREERUNNINGTHEPROGRAMYIELDSTHEFOLLOWINGOUTPUTCALLINGWITHONEARGUMENTTRACESELECTHELLO_NEWMANJERRYHELLO_NEWMANJERRYHELLOJERRYCALLINGWITHTWOARGUMENTSEXECUTEERRORWRONGNUMBEROFARGUMENTSTOFUNCTIONHELLO_NEWMANCALLINGWITHNOARGUMENTSEXECUTEERRORWRONGNUMBEROFARGUMENTSTOFUNCTIONHELLO_NEWMANTHEFIRSTCALLCONSISTSOFJUSTONEARGUMENTSINCETHEEXAMPLEREGISTEREDTHEFUNCTIONASTAKINGEXACTLYONEARGUMENT,ITSUCCEEDSTHESECONDCALLATTEMPTSTOUSETWOARGUMENTS,WHICHFAILSTHETHIRDCALLUSESNOARGUMENTS,ANDALSOFAILSANDTHEREYOUHAVEITASQLITEEXTENSIONFUNCTIONTHISDOESBRINGUPAFEWNEWFUNCTIONSTHATIHAVENOTADDRESSEDYETTHEFIRSTFEWFUNCTIONSARESPECIFICTOTHECOMMONCODETHEFUNCTIONLOG_SQLSIMPLYCALLSSQLITE3_TRACE,PASSINGINATRACINGFUNCTIONTHATPREFIXESTHETRACEDSQLWITHTHEWORDTRACEIUSETHISSOYOUCANSEEWHATISHAPPENINGINTHEEXAMPLEASTHESQLISEXECUTEDTHESECONDFUNCTIONISPRINT_SQL_RESULT,WHICHHASTHEFOLLOWINGDECLARATIONINTPRINT_SQL_RESULTSQLITE3DB,CONSTCHARSQL,THISISASIMPLEWRAPPERAROUNDSQLITE3_PREPAREANDFRIENDSTHATEXECUTESASQLSTATEMENTANDPRINTSTHERESULTSRETURNVALUESTHISEXAMPLEINTRODUCESANEWSQLITEFUNCTIONSQLITE3_RESULT_TEXTTHISFUNCTIONISJUSTONEOFAFAMILYOFSQLITE_RESULT_XXXFUNCTIONSUSEDTOSETRETURNVALUESFORUSERDEFINEDFUNCTIONSANDAGGREGATESTHESCALARFUNCTIONSAREASFOLLOWSVOIDSQLITE3_RESULT_DOUBLESQLITE3_CONTEXT,DOUBLEVOIDSQLITE3_RESULT_INTSQLITE3_CONTEXT,INTVOIDSQLITE3_RESULT_INT64SQLITE3_CONTEXT,LONGLONGINTVOIDSQLITE3_RESULT_NULLSQLITE3_CONTEXTTHESEFUNCTIONSSIMPLYTAKEASECONDARGUMENTOFTHETYPESPECIFIEDINTHEFUNCTIONNAMEANDSETITASTHERETURNVALUEOFTHEFUNCTIONTHEARRAYFUNCTIONSAREVOIDSQLITE3_RESULT_TEXTSQLITE3_CONTEXT,CONSTCHAR,INTN,VOIDVOIDVOIDSQLITE3_RESULT_BLOBSQLITE3_CONTEXT,CONSTVOID,INTN,VOIDVOIDTHESEFUNCTIONSTAKEARRAYDATAANDSETTHATDATAASTHERETURNVALUEFORTHEFUNCTIONTHEYHAVETHEGENERALFORMVOIDSQLITE3_RESULT_XXXSQLITE3_CONTEXTCTX,/FUNCTIONCONTEXT/CONSTXXXVALUE,/ARRAYVALUE/INTLEN,/ARRAYLENGTH/VOIDFREEVOID/ARRAYCLEANUPFUNCTION/HEREXXXISTHEPARTICULARARRAYTYPEVOIDFORBLOBSORCHARFORTEXTAGAIN,IFYOUREADCHAPTER6,YOUMAYFINDTHESEFUNCTIONSSUSPICIOUSLYSIMILARTOTHESQLITE3_BIND_XXXFUNCTIONS,WHICHTHEYARESETTINGARETURNVALUEFORAFUNCTIONIS,FORALLINTENTSANDPURPOSES,IDENTICALTOBINDINGAVALUETOAPARAMETERIZEDSQLSTATEMENTYOUCOULDEVENPERHAPSREFERTOITAS“BINDINGARETURNVALUE”ARRAYSANDCLEANUPHANDLERSJUSTASINBINDINGARRAYVALUESTOSQLSTATEMENTS,THESEFUNCTIONSWORKINTHESAMEWAYASSQLITE3_BIND_XXXTHEYREQUIREAPOINTERTOTHEARRAY,THELENGTHORSIZEOFTHEARRAY,ANDAFUNCTIONPOINTERTOACLEANUPFUNCTIONTHISCLEANUPFUNCTIONPOINTERCANBEASSIGNEDTHESAMEPREDEFINEDMEANINGSASINSQLITE3_BIND_XXXDEFINESQLITE_STATICVOIDVOID0DEFINESQLITE_TRANSIENTVOIDVOID1SQLITE_STATICMEANSTHATTHEARRAYMEMORYRESIDESINUNMANAGEDSPACE,ANDTHEREFORESQLITESHOULDNOTATTEMPTTOCLEANITUPSQLITE_TRANSIENTTELLSSQLITETHATTHEARRAYDATAISSUBJECTTOCHANGE,ANDTHEREFORESQLITENEEDSTOMAKEITSOWNCOPYINTHISCASE,SQLITEWILLCOPYTHEDATAANDFREEITAFTERTHEFUNCTIONRETURNSTHETHIRDOPTIONISTOPASSINANACTUALFUNCTIONPOINTERTOACLEANUPFUNCTIONOFTHEFORMVOIDCLEANUPVOIDINTHISCASE,SQLITEWILLCALLTHECLEANUPFUNCTIONAFTERTHEUSERDEFINEDFUNCTIONCOMPLETESTHISISTHEMETHODUSEDINTHEPREVIOUSEXAMPLEIUSEDSQLITE3_MPRINTFTOGENERATENEWMANSREPLY,WHICHALLOCATEDASTRINGONTHEHEAPITHENPASSEDINSQLITE3_FREEASTHECLEANUPFUNCTIONTOSQLITE3_RESULT_TEXT,WHICHCOULDFREETHESTRINGMEMORYWHENTHEEXTENSIONFUNCTIONCOMPLETEDERRORCONDITIONSSOMETIMESFUNCTIONSENCOUNTERERRORS,INWHICHCASETHERETURNVALUESHOULDBESETAPPROPRIATELYTHISISWHATSQLITE3_RESULT_ERRORISFORITISDECLAREDASFOLLOWSVOIDSQLITE3_RESULT_ERRORSQLITE3_CONTEXTCTX,/THEFUNCTIONCONTEXT/CONSTCHARMSG,/THEERRORMESSAGE/INTLEN/LENGTHOFTHEERRORMESSAGE/THISTELLSSQLITETHATTHEREWASANERROR,THEDETAILSOFWHICHARECONTAINEDINMSGSQLITEWILLABORTTHECOMMANDTHATCALLEDTHEFUNCTIONANDSETTHEERRORMESSAGETOTHEVALUECONTAINEDINMSGRETURNINGINPUTVALUESSOMETIMES,YOUMAYWANTTOPASSBACKANARGUMENTASTHERETURNVALUEINTHEEXACTSAMEFORMRATHERTHANYOURHAVINGTODETERMINETHEARGUMENTSTYPE,EXTRACTITSVALUEWITHTHECORRESPONDINGSQLITE3_COLUMN_XXXFUNCTION,ANDTHENTURNRIGHTAROUNDANDSETTHERETURNVALUEWITHTHEAPPROPRIATESQLITE3_RESULT_XXXFUNCTION,THEAPIOFFERSSQLITE3_RESULT_VALUESOYOUCANDOALLOFTHISINONEFELLSWOOPITISDECLAREDASFOLLOWSVOIDSQLITE3_RESULT_VALUESQLITE3_CONTEXTCTX,/THEFUNCTIONCONTEXT/SQLITE3_VALUEVALUE/THEARGUMENTVALUE/FOREXAMPLE,SAYYOUWANTEDTOCREATEAFUNCTIONECHOTHATSPITSBACKITSFIRSTARGUMENTTHEIMPLEMENTATIONISASFOLLOWSVOIDECHOSQLITE3_CONTEXTCTX,INTNARGS,SQLITE3_VALUEVALUESSQLITE3_RESULT_VALUECTX,VALUES0ITWOULDWORKFROMSQLASFOLLOWSSQLITESELECTECHOHELLOJERRYASREPLYREPLYHELLOJERRYEVENBETTER,ECHOWORKSEQUALLYWELLWITHARGUMENTSOFANYSTORAGECLASS,ANDRETURNSTHEMACCORDINGLYSQLITESELECTECHO314ASREPLY,TYPEOFECHO314ASTYPEREPLYTYPE314REALSQLITESELECTECHOX0128ASREPLY,TYPEOFECHOX0128ASTYPEREPLYTYPEBLOBSQLITESELECTECHONULLASREPLY,TYPEOFECHONULLASTYPEREPLYTYPENULLACOMPLETEEXAMPLELETSMOVEONTOACOMPLETEEXAMPLETHATUSESMOSTOFTHEAPIFUNCTIONSDESCRIBEDEARLIERTHISWILLGIVEYOUABETTERFEELFORALLTHATISAVAILABLETOYOUINONEPLACEWEWILLIMPLEMENTAFUNCTIONCALLEDFUNCTION,WHICHTAKESAVARIABLENUMBEROFARGUMENTSITWILLPRINTTHEARGUMENTTYPESANDRETURNANINTEGERVALUEIF,HOWEVER,THEFIRSTARGUMENTISTHESTRINGVALUEFAIL,ITWILLCALLTHEERRORHANDLER,RETURNINGANERRORMESSAGETHEMAINFUNCTION,SHOWNINLISTING72,ISMUCHTHESAMEASTHEPREVIOUSEXAMPLETHECOMPLETEEXAMPLEISLOCATEDINFUNCCAGAIN,SOMEOFTHEERRORHANDLINGHASBEENEXCISEDFORCLARITYLISTING72THEMAINFUNCTIONINTMAININTARGC,CHARARGVINTRCSQLITE3DBCONSTCHARSQLSQLITE3_OPEN“TESTDB“,SQLITE3_CREATE_FUNCTIONDB,“FUNCTION“,1,SQLITE_UTF8,NULL,FUNCTION,NULL,NULL/TURNONSQLLOGGING/LOG_SQLDB,1/CALLFUNCTIONWITHONETEXTARGUMENT/EXECUTEDB,“SELECTFUNCTION1“/CALLFUNCTIONWITHSEVERALARGUMENTSOFVARIOUSTYPES/EXECUTEDB,“SELECTFUNCTION1,271828“/CALLFUNCTIONWITHVARIABLEARGUMENTS,THEFIRSTARGUMENTSVALUEBEINGFAILTHISWILLTRIGGERTHEFUNCTIONTOCALLSQLITE3_RESULT_ERROR/EXECUTEDB,“SELECTFUNCTIONFAIL,1,271828,THREE,X0004,NULL“/DONE/SQLITE3_CLOSEDBRETURN0NOTETHE1VALUEFORTHENARGARGUMENTINSQLITE3_CREATE_FUNCTIONTHISCORRESPONDSTOTHENUMBEROFREQUIREDARGUMENTSTHATMUSTBEPROVIDEDTOTHEFUNCTIONUSING1TELLSSQLITETHATTHEFUNCTIONACCEPTSAVARIABLENUMBEROFARGUMENTSNOTETHATTHEREISANEWCONVENIENCEFUNCTIONHERECALLEDEXECUTETHISISJUSTATHINWRAPPERAROUNDSQLITE3_EXECTHATEXECUTESASQLCOMMANDANDREPORTSANYERRORSTOSTANDARDERROR,IFANYITWASLISTEDINCHAPTER6ANDISPARTOFTHECOMMONLIBRARYTHEFUNCTIONSIMPLEMENTATIONISSHOWNINLISTING73外文原文扩展CAPI技术这一章是关于教授SQLITE新技巧的。前一章是研究通用数据库技术，这一章是研究正在发展的部分。API的后半部