Lecture13

Structures&UnionsCProgrammingLanguageOutlineBasicsofStructureArrayofStructureStructuresandFunctionstypedefUnionTypesandVariablesMemoryAllocationofUnionVariablesBasicsofStructureStructureisacompounddatatype,itcancontainsmemberswithdifferenttypes.Youmustdeclareastructuretypefirst,thenusethistypetodefineastructurevariable,andthenyouareabletousethevariable.DeclarationofStructureSyntaxstructName { DeclarationofMembers };Example

structstudent_info { charid[10];charname[20];charsex;intage;floatscores[8];};Examplestructtime{inttm_sec;/*secondsaftertheminute(0,59)*/inttm_min;/*minutesafterthehour(0,59)*/inttm_hour;/*hourssincemidnight(0,23)*/inttm_mday;/*dayofthemonth(1,31)*/inttm_mon;/*monthssinceJanuary(0,11)*/inttm_year;/*yearssince1900*/inttm_wday;/*dayssinceSunday(0,6)*/inttm_yday;/*dayssinceJanuary1(0,365)*/};StructureVariableThreewaystodefineastructurevariable1)Declarethetypefirst,usethetypetodefinethevariablesSyntax:structType_NameVariable_Name;

structstudent_infostu1;

structstudent_infostu2,stu3;StructureVariable2)Combinethedeclarationanddefinitionstructstudent_info{charid[10];charname[20];intscore;}stu1,stu2,stu3;StructureVariable3)AnonymousDeclarationstruct{charid[10];charname[20];intscore;

}stu1,stu2,stu3;StructureVariableThesizeofmemoryunitsthatoccupiedbyastructurevariableisthesummationofmemoriesthatoccupiedbyallofitsmembers.Pleasenotesomecompilerswillallocatemoreunitsofmemoryforastructurevariablethanitneededforthepurposetogetabetterprocessperformance.StructureVariableTogettheactualmemorysizethatastructurevariableuses,youcanuseoperatorsizeof.Suchassizeof(strucutstudent)or

sizeofstu1DeclarationofStructureMemberofastructurecanalsobeastructuretype.Example

structdate_type {intyear; intmonth;intday;}； structstudent_info {charid[10];charname[20];

structdate_typebirthday;}；InitiationAssignthevaluetoeachmemberrespectively.Suchas:structstudent_infostu1={“1234567890”,

“Tom”,‘M’,{1988,8,8}};structstudent_infostu2={“1234567890”,

“Tom”,‘M’,1988,8,8};OperationsThestructurevariablescandooperationsasawholeonfollowing:Assignmentoperationmustbeonsametypestructuresvariables.Thevalueofeachmemberwillbeassignedrespectively.Useastheargumenttopassthevalue,oruseasthereturnvalue.OperationsThestructurevariablescanNOTdooperationsasawholeonfollowing:InputandoutputArithmeticandcomparisonButmembersofstructurevariablecandoaboveoperationsjustasindividualvariables..Operator.operatorisusedtoreferthememberofstructurevariables.Syntax:variable.memberstu1.idstu3.birthday.yearExample1,2,3ArrayofStructureElementsofanarrayarestructuretype.Declarethestructure,definethearray,usetheindextorefertheelementofarrayandusethe.operatortoreferthememberofstructure.Example4StructuresandFunctionsStructurevariablesasawhole,oreachmembersofthestructurevariablescanworkastheargumentorreturnvalueofthefunctions.Example5,6typedeftypedefkeywordisusedtodefineanewtypebasedonacurrenttype.Syntax:

typedeftypeNew_Type;typedefintINTEGER;typedefstructstuSTUDENT;typedefstructstu{…}STUDENT;typedefThenewtypenamedefinedbytypedefareequivalenttotheoldone.Thenewoneandtheoldonecanbeusedalternatively.typedefstructstudent_infoSTUDENT;STUDENTstu1,stu2;structstudent_infostu3;UnionsUnionisaspecialdatatype.Itcontainsmembers,andallmemberssharethesameamountofmemory.Theuseofunionissimilarwithstructure,declarefirst,anddefinethevariablelater.UnionDeclarationsunionName

{DeclarationofMembers;

}；

uniondemo{floatf_value;inti_value;doubled_value;};UnionDefinitionsuniondemounion1;uniondemo{floatf_value;inti_value;doubled_value;}union2;UnionInitializationsToinitializeaninstanceofaunionwhiledefiningit,youcaninitializeitonlywithaconstantofthesametypeasthefirstvariableintheunion.UnionInitializationsuniondemo{floatf_value;inti_value;doubled_value;}union1={3.14f};oruniondemounion2=3.14f;

UnionOperationsSimilarwithstructuresunion1.f_value=2.5;union2.i_value++;union3.d_value=uionn1.d_value;Example7MemoryAllocationofUnionVariables

i_value

f_value

d_valueUnionOperationsExample8