C++常見英文面試筆試題資料僅供參考C/C++ProgramminginterviewquestionsandanswersBySatishShetty,July14th,Whatisencapsulation??

Containingandhidinginformationaboutanobject,suchasinternaldatastructuresandcode.Encapsulationisolates(使隔離)theinternalcomplexityofanobject'soperationfromtherestoftheapplication.Forexample,aclientcomponentaskingfornetrevenue（收益）fromabusinessobjectneednotknowthedata'sorigin.

Whatisinheritance?Inheritanceallowsoneclasstoreusethestateandbehaviorofanotherclass.Thederivedclassinheritsthepropertiesandmethodimplementationsofthebaseclassandextendsitbyoverridingmethodsandaddingadditionalpropertiesandmethods.

WhatisPolymorphism??Polymorphismallowsaclienttotreatdifferentobjectsinthesamewayeveniftheywerecreatedfromdifferentclassesandexhibit（展現(xiàn)）differentbehaviors.Youcanuseimplementation（實現(xiàn)）inheritancetoachievepolymorphisminlanguagessuchasC++andJava.Baseclassobject'spointercaninvoke（調用）methodsinderivedclassobjects.YoucanalsoachievepolymorphisminC++byfunctionoverloadingandoperatoroverloading.

Whatisconstructororctor?Constructorcreatesanobjectandinitializesit.Italsocreatesvtable變量列表？forvirtualfunctions.Itisdifferentfromothermethodsinaclass.

Whatisdestructor?Destructorusuallydeletesanyextraresourcesallocatedbytheobject.

Whatisdefaultconstructor?Constructorwithnoargumentsoralltheargumentshasdefaultvalues.

Whatiscopyconstructor?Constructorwhichinitializestheit'sobjectmembervariables(byshallowcopying)withanotherobjectofthesameclass.Ifyoudon'timplementoneinyourclassthencompilerimplementsoneforyou.forexample:

BooObj1(10);//callingBooconstructorBooObj2(Obj1);//callingboocopyconstructor

BooObj2=Obj1;//callingboocopyconstructorWhenarecopyconstructorscalled?Copyconstructorsarecalledinfollowingcases:

a)whenafunctionreturnsanobjectofthatclassbyvalue

b)whentheobjectofthatclassispassedbyvalueasanargumenttoafunction

c)whenyouconstructanobjectbasedonanotherobjectofthesameclass

d)Whencompilergeneratesatemporaryobject

Whatisassignmentoperator?Defaultassignmentoperatorhandlesassigningoneobjecttoanotherofthesameclass.Membertomembercopy(shallowcopy)

Whatarealltheimplicitmemberfunctionsoftheclass?Orwhatareallthefunctionswhichcompilerimplementsforusifwedon'tdefineone.??defaultctor

copyctor

assignmentoperator

defaultdestructor

addressoperator

Whatisconversionconstructor?constructorwithasingleargumentmakesthatconstructorasconversionctoranditcanbeusedfortypeconversion.forexample:classBoo

{

public:

Boo(inti);

};

BooBooObject=10;//assigningint10Booobject

Whatisconversionoperator??

classcanhaveapublicmethodforspecificdatatypeconversions.forexample:

classBoo

{

doublevalue;

public:

Boo(inti)

operatordouble()

{

returnvalue;

}

};

BooBooObject;

doublei=BooObject;//assigningobjecttovariableioftypedouble.nowconversionoperatorgetscalledtoassignthevalue.

Whatisdiffbetweenmalloc()/free()andnew/delete?mallocallocatesmemoryforobjectinheapbutdoesn'tinvokeobject'sconstructortoinitiallizetheobject.newallocatesmemoryandalsoinvokesconstructortoinitializetheobject.malloc()andfree()donotsupportobjectsemantics

Doesnotconstructanddestructobjects

string*ptr=(string*)(malloc(sizeof(string)))

Arenotsafe

Doesnotcalculatethesizeoftheobjectsthatitconstruct

Returnsapointertovoid

int*p=(int*)(malloc(sizeof(int)));

int*p=newint;

Arenotextensible

newanddeletecanbeoverloadedinaclass"delete"firstcallstheobject'sterminationroutine(i.e.itsdestructor)andthenreleasesthespacetheobjectoccupiedontheheapmemory.Ifanarrayofobjectswascreatedusingnew,thendeletemustbetoldthatitisdealingwithanarraybyprecedingthenamewithanempty[]:-Int_t*my_ints=newInt_t[10];...delete[]my_ints;

whatisthediffbetween"new"and"operatornew"?

"operatornew"workslikemalloc.

Whatisdifferencebetweentemplateandmacro??Thereisnowayforthecompilertoverifythatthemacroparametersareofcompatibletypes.Themacroisexpandedwithoutanyspecialtypechecking.Ifmacroparameterhasapost-incrementedvariable(likec++),theincrementisperformedtwotimes.Becausemacrosareexpandedbythepreprocessor,compilererrormessageswillrefertotheexpandedmacro,ratherthanthemacrodefinitionitself.Also,themacrowillshowupinexpandedformduringdebugging.forexample:Macro:#definemin(i,j)(i<j?i:j)template:

template<classT>

Tmin(Ti,Tj)

{

returni<j?i:j;

}

WhatareC++storageclasses?auto

register

static

externauto:thedefault.Variablesareautomaticallycreatedandinitializedwhentheyaredefinedandaredestroyedattheendoftheblockcontainingtheirdefinition.Theyarenotvisibleoutsidethatblockregister:atypeofautovariable.asuggestiontothecompilertouseaCPUregisterforperformancestatic:avariablethatisknownonlyinthefunctionthatcontainsitsdefinitionbutisneverdestroyedandretains=keepitsvaluebetweencallstothatfunction.Itexistsfromthetimetheprogrambeginsexecutionextern:astaticvariablewhosedefinitionandplacementisdeterminedwhenallobjectandlibrarymodulesarecombined(linked)toformtheexecutablecodefile.Itcanbevisibleoutsidethefilewhereitisdefined.

WhatarestoragequalifiersinC++?Theyare..const

volatile

mutableConstkeywordindicatesthatmemoryonceinitialized,shouldnotbealteredbyaprogram.volatilekeywordindicatesthatthevalueinthememorylocationcanbealteredeventhoughnothingintheprogram

codemodifiesthecontents.forexampleifyouhaveapointertohardwarelocationthatcontainsthetime,wherehardwarechangesthevalueofthispointervariableandnottheprogram.Theintentofthiskeywordtoimprovetheoptimizationabilityofthecompiler.mutablekeywordindicatesthatparticularmemberofastructureorclasscanbealteredevenifaparticularstructurevariable,class,orclassmemberfunctionisconstant.structdata

{

charname[80];

mutabledoublesalary;

}constdataMyStruct={"SatishShetty",1000};//initlizedbycomplierstrcpy(MyS,"ShilpaShetty");//compilererror

MyStruct.salaray=;//complierishappyallowed

Whatisreference??referenceisanamethatactsasanalias,oralternativename,forapreviouslydefinedvariableoranobject.prependingvariablewith"&"symbolmakesitasreference.forexample:inta;

int&b=a;&讀amp

Whatispassingbyreference?Methodofpassingargumentstoafunctionwhichtakesparameteroftypereference.forexample:voidswap(int&x,int&y)

{

inttemp=x;

x=y;

y=temp;

}inta=2,b=3;swap(a,b);

Basically,insidethefunctiontherewon'tbeanycopyofthearguments"x"and"y"insteadtheyrefertooriginalvariablesaandb.sonoextramemoryneededtopassargumentsanditismoreefficient.

Whendouse"const"referenceargumentsinfunction?a)Usingconstprotectsyouagainstprogrammingerrorsthatinadvertently不經(jīng)意的alterdata.

b)Usingconstallowsfunctiontoprocessbothconstandnon-constactualarguments,whileafunctionwithoutconstintheprototypecanonlyacceptnonconstantarguments.

c)Usingaconstreferenceallowsthefunctiontogenerateanduseatemporaryvariableappropriately.

WhenaretemporaryvariablescreatedbyC++compiler?Providedthatfunctionparameterisa"constreference",compilergeneratestemporaryvariableinfollowing2ways.a)Theactualargumentisthecorrecttype,butitisn'tLvaluedoubleCube(constdouble&num)

{

num=num*num*num;

returnnum;}doubletemp=2.0;

doublevalue=cube(3.0+temp);//argumentisaexpressionandnotaLvalue;

b)Theactualargumentisofthewrongtype,butofatypethatcanbeconvertedtothecorrecttypelongtemp=3L;

doublevalue=cuberoot(temp);//longtodoubleconversion

Whatisvirtualfunction?

Whenderivedclassoverridesthebaseclassmethodbyredefiningthesamefunction,thenifclientwantstoaccessredefinedthemethodfromderivedclassthroughapointerfrombaseclassobject,thenyoumustdefinethisfunctioninbaseclassasvirtualfunction.classparent

{

voidShow()

{

cout<<"i'mparent"<<endl;

}

};

classchild:publicparent

{

voidShow()

{

cout<<"i'mchild"<<endl;

}};

parent*parent_object_ptr=newchild;parent_object_ptr->show()//callsparent->show()i

nowwegotovirtualworld...classparent

{

virtualvoidShow()

{

cout<<"i'mparent"<<endl;

}

};

classchild:publicparent

{

voidShow()

{

cout<<"i'mchild"<<endl;

}};

parent*parent_object_ptr=newchild;parent_object_ptr->show()//callschild->show()

Whatispurevirtualfunction?orwhatisabstractclass?

Whenyoudefineonlyfunctionprototypeinabaseclasswithoutimplementationanddothecompleteimplementation實現(xiàn)inderivedclass.Thisbaseclassiscalledabstractclassandclientwon'tabletoinstantiateanobjectusingthisbaseclass.Youcanmakeapurevirtualfunctionorabstractclassthisway..classBoo

{

voidfoo()=0;

}

BooMyBoo;//compilationerror

WhatisMemoryalignment??Thetermalignmentprimarilymeansthetendency趨向ofanaddresspointervaluetobeamultipleofsomepoweroftwo.Soapointerwithtwobytealignmenthasazerointheleastsignificantbit.Andapointerwithfourbytealignmenthasazeroinboththetwoleastsignificantbits.Andsoon.Morealignmentmeansalongersequenceofzerobitsinthelowestbitsofapointer.

Whatproblemdoesthenamespacefeaturesolve?Multipleprovidersoflibrariesmightusecommonglobalidentifierscausinganamecollisionwhenanapplicationtriestolinkwithtwoormoresuchlibraries.Thenamespacefeaturesurroundsalibrary'sexternaldeclarationswithauniquenamespacethateliminates消除space[identifier]{namespace-body}Anamespacedeclarationidentifiesandassignsanametoadeclarativeregion.

Theidentifierinanamespacedeclarationmustbeuniqueinthedeclarativeregioninwhichitisused.Theidentifieristhenameofthenamespaceandisusedtoreferenceitsmembers.

Whatistheuseof'using'declaration?Ausingdeclarationmakesitpossibletouseanamefromanamespacewithoutthescope范圍operator.

WhatisanIterator迭代器class?Aclassthatisusedtotraversethrough穿過theobjectsmaintainedbyacontainerclass.Therearefivecategoriesofiterators:inputiterators,outputiterators,forwarditerators,bidirectionaliterators,randomaccess.Aniteratorisanentitythatgivesaccesstothecontentsofacontainerobjectwithoutviolatingencapsulationconstraints.Accesstothecontentsisgrantedonaone-at-a-timebasisinorder.Theordercanbestorageorder(asinlistsandqueues)orsomearbitraryorder(asinarrayindices)oraccordingtosomeorderingrelation(asinanorderedbinarytree).Theiteratorisaconstruct,whichprovidesaninterfacethat,whencalled,yieldseitherthenextelementinthecontainer,orsomevaluedenotingthefactthattherearenomoreelementstoexamine.Iteratorshidethedetailsofaccesstoandupdateoftheelementsofacontainerclass.Somethinglikeapointer.

Whatisadangling懸掛pointer?Adanglingpointerariseswhenyouusetheaddressofanobjectafteritslifetimeisover.Thismayoccurinsituationslikereturningaddressesoftheautomaticvariablesfromafunctionorusingtheaddressofthememoryblockafteritisfreed.

WhatdoyoumeanbyStackunwinding?Itisaprocessduringexceptionhandlingwhenthedestructoriscalledforalllocalobjectsinthestackbetweentheplacewheretheexceptionwasthrownandwhereitiscaught.

拋出異常與棧展開（stackunwinding）拋出異常時，將暫停當前函數(shù)的執(zhí)行，開始查找匹配的catch子句。首先檢查throw本身是否在try塊內部，如果是，檢查與該try相關的catch子句，看是否能夠處理該異常。如果不能處理，就退出當前函數(shù)，而且釋放當前函數(shù)的內存并銷毀局部對象，繼續(xù)到上層的調用函數(shù)中查找，直到找到一個能夠處理該異常的catch。這個過程稱為棧展開（stackunwinding）。當處理該異常的catch結束之后，緊接著該catch之后的點繼續(xù)執(zhí)行。1.為局部對象調用析構函數(shù)如上所述，在棧展開的過程中，會釋放局部對象所占用的內存并運行類類型局部對象的析構函數(shù)。但需要注意的是，如果一個塊經(jīng)過new動態(tài)分配內存，而且在釋放該資源之前發(fā)生異常，該塊因異常而退出，那么在棧展開期間不會釋放該資源，編譯器不會刪除該指針，這樣就會造成內存泄露。2.析構函數(shù)應該從不拋出異常在為某個異常進行棧展開的時候，析構函數(shù)如果又拋出自己的未經(jīng)處理的另一個異常，將會導致調用標準庫terminate函數(shù)。一般terminate函數(shù)將調用abort函數(shù)，導致程序的非正常退出。因此析構函數(shù)應該從不拋出異常。3.異常與構造函數(shù)如果在構造函數(shù)對象時發(fā)生異常，此時該對象可能只是被部分構造，要保證能夠適當?shù)某蜂N這些已構造的成員。4.未捕獲的異常將會終止程序不能不處理異常。如果找不到匹配的catch，程序就會調用庫函數(shù)terminate。Nametheoperatorsthatcannotbeoverloaded??sizeof,.,.*,.->,::,?:

Whatisacontainerclass?Whatarethetypesofcontainerclasses?Acontainerclassisaclassthatisusedtoholdobjectsinmemoryorexternalstorage.Acontainerclassactsasagenericholder.Acontainerclasshasapredefinedbehaviorandawell-knowninterface.Acontainerclassisasupportingclasswhosepurposeistohidethetopologyusedformaintainingthelistofobjectsinmemory.Whenacontainerclasscontainsagroupofmixedobjects,thecontaineriscalledaheterogeneous不均勻的多樣的container;whenthecontainerisholdingagroupofobjectsthatareallthesame,thecontaineriscalledahomogeneous單一的均勻的container.

Whatisinlinefunction??The__inlinekeywordtellsthecompilertosubstitute替代thecodewithinthefunctiondefinitionforeveryinstanceofafunctioncall.However,substitutionoccursonlyatthecompiler'sdiscretion靈活性.Forexample,thecompilerdoesnotinlineafunctionifitsaddressistakenorifitistoolargetoinline.

使用預處理器實現(xiàn)，沒有了參數(shù)壓棧，代碼生成等一系列的操作,因此，效率很高，這是它在C中被使用的一個主要原因

Whatisoverloading??WiththeC++language,youcanoverloadfunctionsandoperators.Overloadingisthepracticeofsupplyingmorethanonedefinitionforagivenfunctionnameinthesamescope.-Anytwofunctionsinasetofoverloadedfunctionsmusthavedifferentargumentlists.

-Overloadingfunctionswithargumentlistsofthesametypes,basedonreturntypealone,isanerror.

WhatisOverriding?Tooverrideamethod,asubclassoftheclassthatoriginallydeclaredthemethodmustdeclareamethodwiththesamename,returntype(orasubclassofthatreturntype),andsameparameterlist.

Thedefinitionofthemethodoverridingis:

·Musthavesamemethodname.

·Musthavesamedatatype.

·Musthavesameargumentlist.

Overridingamethodmeansthatreplacingamethodfunctionalityinchildclass.Toimplyoverridingfunctionalityweneedparentandchildclasses.Inthechildclassyoudefinethesamemethodsignatureasonedefinedintheparentclass.

Whatis"this"pointer?Thethispointerisapointeraccessibleonlywithinthememberfunctionsofaclass,struct,oruniontype.Itpointstotheobjectforwhichthememberfunctioniscalled.Staticmemberfunctionsdonothaveathispointer.Whenanon-staticmemberfunctioniscalledforanobject,theaddressoftheobjectispassedasahiddenargumenttothefunction.Forexample,thefollowingfunctioncallmyDate.setMonth(3);canbeinterpreted解釋thisway:setMonth(&myDate,3);Theobject'saddressisavailablefromwithinthememberfunctionasthethispointer.Itislegal,thoughunnecessary,tousethethispointerwhenreferringtomembersoftheclass.

Whathappenswhenyoumakecall"deletethis;"??Thecodehastwobuilt-inpitfalls陷阱/誤區(qū).First,ifitexecutesinamemberfunctionforanextern,static,orautomaticobject,theprogramwillprobablycrashassoonasthedeletestatementexecutes.Thereisnoportablewayforanobjecttotellthatitwasinstantiatedontheheap,sotheclasscannotassertthatitsobjectisproperlyinstantiated.Second,whenanobjectcommitssuicidethisway,theusingprogrammightnotknowaboutitsdemise死亡/轉讓.Asfarastheinstantiatingprogramisconcerned有關的,theobjectremainsinscopeandcontinuestoexisteventhoughtheobjectdiditselfin.Subsequent后來的dereferencing間接引用（dereferencingpointer

重引用指針，dereferencingoperator

取值運算符）ofthepointercanandusuallydoesleadtodisaster不幸.Youshouldneverdothis.Sincecompilerdoesnotknowwhethertheobjectwasallocatedonthestackorontheheap,"deletethis"couldcauseadisaster.

Howvirtualfunctionsareimplemented執(zhí)行C++?Virtualfunctionsareimplementedusingatableoffunctionpointers,calledthevtable.Thereisoneentryinthetablepervirtualfunctionintheclass.Thistableiscreatedbytheconstructoroftheclass.Whenaderivedclassisconstructed,itsbaseclassisconstructedfirstwhichcreatesthevtable.Ifthederivedclassoverridesanyofthebaseclassesvirtualfunctions,thoseentriesinthevtableareoverwrittenbythederivedclassconstructor.Thisiswhyyoushouldnevercallvirtualfunctionsfromaconstructor:becausethevtableentriesfortheobjectmaynothavebeensetupbythederivedclassconstructoryet,soyoumightendupcallingbaseclassimplementationsofthosevirtualfunctions

WhatisnamemanglinginC++??Theprocessofencodingtheparametertypeswiththefunction/methodnameintoauniquenameiscallednamemangling.Theinverseprocessiscalleddemangling.ForexampleFoo::bar(int,long)constismangledas`bar__C3Fooil'.

Foraconstructor,themethodnameisleftout.ThatisFoo::Foo(int,long)constismangledas`__C3Fooil'.

Whatisthedifferencebetweenapointerandareference?Areferencemustalwaysrefertosomeobjectand,therefore,mustalwaysbeinitialized;pointersdonothavesuchrestrictions.Apointercanbereassignedtopointtodifferentobjectswhileareferencealwaysreferstoanobjectwithwhichitwasinitialized.Howareprefixandpostfixversionsofoperator++()differentiated?Thepostfixversionofoperator++()hasadummyparameteroftypeint.Theprefixversiondoesnothavedummyparameter.Whatisthedifferencebetweenconstchar*myPointerandchar*constmyPointer?Constchar*myPointerisanonconstantpointertoconstantdata;whilechar*constmyPointerisaconstantpointertononconstantdata.HowcanIhandleaconstructorthatfails?throwanexception.Constructorsdon'thaveareturntype,soit'snotpossibletousereturncodes.Thebestwaytosignalconstructorfailureisthereforetothrowanexception.HowcanIhandleadestructorthatfails?Writeamessagetoalog-file.Butdonotthrowanexception.

TheC++ruleisthatyoumustneverthrowanexceptionfromadestructorthatisbeingcalledduringthe"stackunwinding"processofanotherexception.Forexample,ifsomeonesaysthrowFoo(),thestackwillbeunwoundsoallthestackframesbetweenthethrowFoo()andthe}catch(Fooe){willgetpopped.Thisiscalledstackunwinding.

Duringstackunwinding,allthelocalobjectsinallthosestackframesaredestructed.Ifoneofthosedestructorsthrowsanexception(sayitthrowsaBarobject),theC++runtimesystemisinano-winsituation:shoulditignoretheBarandendupinthe}catch(Fooe){whereitwasoriginallyheaded?ShoulditignoretheFooandlookfora}catch(Bare){handler?Thereisnogoodanswer--eitherchoicelosesinformation.

SotheC++languageguaranteesthatitwillcallterminate()atthispoint,andterminate()killstheprocess.Bangyou'redead.

WhatisVirtualDestructor?

Usingvirtualdestructors,youcandestroyobjectswithoutknowingtheirtype-thecorrectdestructorfortheobjectisinvokedusingthevirtualfunctionmechanism.Notethatdestructorscanalsobedeclaredaspurevirtualfunctionsforabstractclasses.ifsomeonewillderivefromyourclass,andifsomeonewillsay"newDerived",where"Derived"isderivedfromyourclass,andifsomeonewillsaydeletep,wheretheactualobject'stypeis"Derived"butthepointerp'stypeisyourclass.

Canyouthinkofasituationwhereyourprogramwouldcrashwithoutreachingthebreakpointwhichyousetatthebeginningofmain()?C++allowsfordynamicinitializationofglobalvariablesbeforemain()isinvoked.Itispossiblethatinitializationofglobalwillinvokesomefunction.Ifthisfunctioncrashesthecrashwilloccurbeforemain()isentered.

NametwocaseswhereyouMUSTuseinitializationlistasopposedtoassignmentinconstructors.Bothnon-staticconstdatamembersandreferencedatamemberscannotbeassignedvalues;instead,youshoulduseinitializationlisttoinitializethem.

Canyouoverloadafunctionbasedonlyonwhetheraparameterisavalueorareference?No.Passingbyvalueandbyreferencelooksidenticaltothecaller.

WhatarethedifferencesbetweenaC++structandC++class?Thedefaultmemberandbaseclassaccessspecifiers標識符aredifferent.TheC++structhasallthefeaturesoftheclass.Theonlydifferencesarethatastructdefaultstopublicmemberaccessandpublicbaseclassinheritance,andaclassdefaultstotheprivateaccessspecifierandprivatebaseclassinheritance.

Whatdoesextern"C"intfunc(int*,Foo)accomplish實現(xiàn)/達到/完成?Itwillturnoff"namemangling"forfuncsothatonecanlinktocodecompiledbyaCcompiler.

Howdoyouaccessthestaticmemberofaclass?<ClassName>::<StaticMemberName>

Whatismultipleinheritance(virtualinheritance)?Whatareitsadvantagesanddisadvantages?MultipleInheritanceistheprocesswhereby經(jīng)過achildcanbederivedfrommorethanoneparentclass.Theadvantageofmultipleinheritanceisthatitallowsaclasstoinheritthefunctionality功能ofmorethanonebaseclassthus因此allowingformodeling建模ofcomplexrelat