C语言基础教程课件(英文版)ch(1).ppt

AFirstBookofANSICFourthEdition Chapter12Structures AFirstBookofANSIC FourthEdition 2 Objectives SingleStructuresArraysofStructuresPassingandReturningStructuresUnions Optional CommonProgrammingandCompilerErrors AFirstBookofANSIC FourthEdition 3 Introduction EachdataitemlistedinFigure12 1isanentitybyitself calledadatafieldTogether allthedatafieldsformasingleunitcalledarecordInC arecordisreferredtoasastructure AFirstBookofANSIC FourthEdition 4 Introduction continued AFirstBookofANSIC FourthEdition 5 Introduction continued Astructure sformconsistsofthesymbolicnames datatypes andarrangementofindividualdatafieldsintherecordThestructure scontentsconsistoftheactualdatastoredinthesymbolicnames AFirstBookofANSIC FourthEdition 6 Introduction continued AFirstBookofANSIC FourthEdition 7 SingleStructures StructuredefinitioninC struct intmonth intday intyear birth ReservesstoragefortheindividualdataitemslistedinthestructureThethreedataitemsarethemembersofthestructureAssigningactualdatavaluestothedataitemsofastructureiscalledpopulatingthestructure AFirstBookofANSIC FourthEdition 8 spacingofastructuredefinitionisnotrigid SingleStructures continued AFirstBookofANSIC FourthEdition 9 SingleStructures continued Multiplevariablescanbedefinedinonestatementstruct intmonth intday intyear birth current CommontolisttheformofthestructurewithnofollowingvariablenamesThelistofstructuremembersmustbeprecededbyauser selectedstructuretypenamestructDate intmonth intday intyear AFirstBookofANSIC FourthEdition 10 Byconventionthefirstletterofuser selectedstructuretypenamesisuppercase SingleStructures continued AFirstBookofANSIC FourthEdition 11 SingleStructures continued Initializationofstructuresfollowsthesamerulesasfortheinitializationofarrays structDatebirth 12 28 1987 StructurememberscanbeofanydatatypestructPayRecord charname 20 intidNum doubleregRate doubleotRate structPayRecordemployee H Price 12387 15 89 25 50 AFirstBookofANSIC FourthEdition 12 SingleStructures continued AdvantageofstructuresiswhenthesamestructuretypeisusedinalistmanytimesIndividualmemberscanbearraysandstructuresstruct charname 20 structDatebirth person Example person name 4 AFirstBookofANSIC FourthEdition 13 ArraysofStructures AFirstBookofANSIC FourthEdition 14 ArraysofStructures continued AFirstBookofANSIC FourthEdition 15 Innerbracesarenotnecessary ArraysofStructures continued AFirstBookofANSIC FourthEdition 16 ArraysofStructures continued Withoutexplicitinitializers thenumericelementsofbothstaticandexternalarraysorstructuresareinitializedto0 ornulls AninferioralternativetoanarrayofstructuresisparallelarraysParallelarraysaretwoormorearrays whereeacharrayhasthesamenumberofelementsandtheelementsineacharrayaredirectlyrelatedbytheirpositioninthearraysTheyarerarelyusedanymore AFirstBookofANSIC FourthEdition 17 PassingandReturningStructures Individualstructuremembersmaybepassedtoafunctioninthesamemannerasanyscalarvariabledisplay emp idNum calcPay emp payRate emp hours Onmostcompilers completecopiesofallmembersofastructurecanalsobepassedtoafunctionbyincludingthenameofthestructureasanargumenttothecalledfunctioncalcNet emp AFirstBookofANSIC FourthEdition 18 Passbyvalue Althoughthestructuresinmain andcalcNet usethesamegloballydefinedstructuretype thisisnotstrictlynecessary althoughitispreferable PassingandReturningStructures continued AFirstBookofANSIC FourthEdition 19 PassingandReturningStructures continued AstructurecanbepassedbyreferencecalcNet doublecalcNet structEmployee pt pt idNumor pt idNum AFirstBookofANSIC FourthEdition 20 PassingandReturningStructures continued AFirstBookofANSIC FourthEdition 21 PassingandReturningStructures continued AFirstBookofANSIC FourthEdition 22 PassingandReturningStructures continued and canbeappliedtostructures pt hours pt hours pt hours AFirstBookofANSIC FourthEdition 23 PassingandReturningStructures continued AFirstBookofANSIC FourthEdition 24 ReturningStructures AFirstBookofANSIC FourthEdition 25 ReturningStructures continued AFirstBookofANSIC FourthEdition 26 Unions Aunionisadatatypethatreservesthesameareainmemoryfortwoormorevariablesunion charkey intnum doubleprice val Eachofthesetypes butonlyoneatatime canactuallybeassignedtotheunionvariableAunionreservessufficientmemorylocationstoaccommodateitslargestmember sdatatype AFirstBookofANSIC FourthEdition 27 Unions continued IndividualunionmembersareaccessedusingthesamenotationasstructuremembersTypically asecondvariablekeepstrackofthecurrentdatatypestoredintheunionswitch uType case c printf c val key break case i printf d val num break case d printf f val price break default printf Invalidtype c uType AFirstBookofANSIC FourthEdition 28 Unions continued AtypenamecanbeassociatedwithauniontocreatetemplatesunionDateTime longdays doubletime unionDateTimefirst second pt PointerstounionsusethesamenotationaspointerstostructuresUnionsmaybemembersofstructuresandarrays structures arrays andpointersmaybemembersofunions AFirstBookofANSIC FourthEdition 29 Unions continued struct charuType union char text doublerate uTax flag rateisreferencedasflag uTax rateThefirstcharacterofthestringwhoseaddressisstoredinthepointertextisaccessedas flag uTax text AFirstBookofANSIC FourthEdition 30 CommonProgrammingErrors Attemptingtousestructuresandunions ascompleteentities inrelationalexpressionsAssigninganincorrectaddresstoapointerthatisamemberofastructureorunionStoringonedatatypeinaunionandaccessingitbythewrongvariablenamecanresultinanerrorthatisparticularlytroublesometolocate AFirstBookofANSIC FourthEdition 31 CommonC