C常见英文面试笔试题.docx

C常见英文面试笔试题.docx

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C常见英文面试笔试题

ThefinalrevisionwasonNovember23,2020

C常见英文面试笔试题

C/C++Programminginterviewquestionsandanswers

BySatishShetty,July14th,2004

Whatisencapsulation

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

Whatisinheritance

Inheritanceallowsoneclasstoreusethestateandbehaviorofanotherclass.Thederivedclassinheritsthepropertiesandmethodimplementationsofthebaseclassandextendsitbyoverridingmethodsandaddingadditionalpropertiesandmethods.

WhatisPolymorphism

Polymorphismallowsaclienttotreatdifferentobjectsinthesamewayeveniftheywerecreatedfromdifferentclassesandexhibit（展现）differentbehaviors.

Youcanuseimplementation（实现）inheritancetoachievepolymorphisminlanguagessuchasC++andJava.

Baseclassobject'spointercaninvoke（调用）methodsinderivedclassobjects.

YoucanalsoachievepolymorphisminC++byfunctionoverloadingandoperatoroverloading.

Whatisconstructororctor

Constructorcreatesanobjectandinitializesit.Italsocreatesvtable变量列表forvirtualfunctions.Itisdifferentfromothermethodsinaclass.

Whatisdestructor

Destructorusuallydeletesanyextraresourcesallocatedbytheobject.

Whatisdefaultconstructor

Constructorwithnoargumentsoralltheargumentshasdefaultvalues.

Whatiscopyconstructor

Constructorwhichinitializestheit'sobjectmembervariables（byshallowcopying）withanotherobjectofthesameclass.Ifyoudon'timplementoneinyourclassthencompilerimplementsoneforyou.

forexample:

BooObj1（10）;Membertomembercopy（shallowcopy）

WhatarealltheimplicitmemberfunctionsoftheclassOrwhatareallthefunctionswhichcompilerimplementsforusifwedon'tdefineone.

defaultctorcopyctorassignmentoperatordefaultdestructoraddressoperator

Whatisconversionconstructor

constructorwithasingleargumentmakesthatconstructorasconversionctoranditcanbeusedfortypeconversion.

forexample:

classBoo{public:

Boo（inti）;};

BooBooObject=10;forexample:

classBoo{doublevalue;public:

Boo（inti）operatordouble（）{returnvalue;}};

BooBooObject;

doublei=BooObject;nowconversionoperatorgetscalledtoassignthevalue.

Whatisdiffbetweenmalloc（）/free（）andnew/delete

mallocallocatesmemoryforobjectinheapbutdoesn'tinvokeobject'sconstructortoinitiallizetheobject.

newallocatesmemoryandalsoinvokesconstructortoinitializetheobject.

malloc（）andfree（）donotsupportobjectsemanticsDoesnotconstructanddestructobjectsstring*ptr=（string*）（malloc（sizeof（string）））ArenotsafeDoesnotcalculatethesizeoftheobjectsthatitconstructReturnsapointertovoidint*p=（int*）（malloc（sizeof（int）））;int*p=newint;Arenotextensiblenewanddeletecanbeoverloadedinaclass

"delete"firstcallstheobject'sterminationroutine.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）

template:

template

Tmin（Ti,Tj）

{

returni

j;}

WhatareC++storageclasses

autoregisterstaticextern

auto:

thedefault.Variablesareautomaticallycreatedandinitializedwhentheyaredefinedandaredestroyedattheendoftheblockcontainingtheirdefinition.Theyarenotvisibleoutsidethatblock

register:

atypeofautovariable.asuggestiontothecompilertouseaCPUregisterforperformance

static:

avariablethatisknownonlyinthefunctionthatcontainsitsdefinitionbutisneverdestroyedandretains=keepitsvaluebetweencallstothatfunction.Itexistsfromthetimetheprogrambeginsexecution

extern:

astaticvariablewhosedefinitionandplacementisdeterminedwhenallobjectandlibrarymodulesarecombined（linked）toformtheexecutablecodefile.Itcanbevisibleoutsidethefilewhereitisdefined.

WhatarestoragequalifiersinC++

Theyare..

constvolatilemutable

Constkeywordindicatesthatmemoryonceinitialized,shouldnotbealteredbyaprogram.

volatilekeywordindicatesthatthevalueinthememorylocationcanbealteredeventhoughnothingintheprogramcodemodifiesthecontents.forexampleifyouhaveapointertohardwarelocationthatcontainsthetime,wherehardwarechangesthevalueofthispointervariableandnottheprogram.Theintentofthiskeywordtoimprovetheoptimizationabilityofthecompiler.

mutablekeywordindicatesthatparticularmemberofastructureorclasscanbealteredevenifaparticularstructurevariable,class,orclassmemberfunctionisconstant.

structdata{charname[80];mutabledoublesalary;}

constdataMyStruct={"SatishShetty",1000};prependingvariablewith"&"symbolmakesitasreference.

forexample:

inta;int&b=a;

&读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不经意的alterdata.b）Usingconstallowsfunctiontoprocessbothconstandnon-constactualarguments,whileafunctionwithoutconstintheprototypecanonlyacceptnonconstantarguments.c）Usingaconstreferenceallowsthefunctiontogenerateanduseatemporaryvariableappropriately.

WhenaretemporaryvariablescreatedbyC++compiler

Providedthatfunctionparameterisa"constreference",compilergeneratestemporaryvariableinfollowing2ways.

a）Theactualargumentisthecorrecttype,butitisn'tLvalue

doubleCube（constdouble&num）{num=num*num*num;returnnum;

}

doubletemp=;

doublevalue=cube+temp）;classparent{voidShow（）{cout<<"i'mparent"<

classchild:

publicparent{voidShow（）{cout<<"i'mchild"<

};

parent*parent_object_ptr=newchild;

parent_object_ptr->show（）.

classparent{virtualvoidShow（）{cout<<"i'mparent"<

classchild:

publicparent{voidShow（）{cout<<"i'mchild"<

};

parent*parent_object_ptr=newchild;

parent_object_ptr->show（）Thisbaseclassiscalledabstractclassandclientwon'tabletoinstantiateanobjectusingthisbaseclass.

Youcanmakeapurevirtualfunctionorabstractclassthisway..

classBoo{voidfoo（）=0;}

BooMyBoo;Soapointerwithtwobytealignmenthasazerointheleastsignificantbit.Andapointerwithfourbytealignmenthasazeroinboththetwoleastsignificantbits.Andsoon.Morealignmentmeansalongersequenceofzerobitsinthelowestbitsofapointer.

Whatproblemdoesthenamespacefeaturesolve

Multipleprovidersoflibrariesmightusecommonglobalidentifierscausinganamecollisionwhenanapplicationtriestolinkwithtwoormoresuchlibraries.Thenamespacefeaturesurroundsalibrary'sexternaldeclarationswithauniquenamespacethateliminates消除thepotentialforthosecollisions.

namespace[identifier]{namespace-body}

Anamespacedeclarationidentifiesandassignsanametoadeclarativeregion.Theidentifierinanamespacedeclarationmustbeuniqueinthedeclarativeregioninwhichitisused.Theidentifieristhenameofthenamespaceandisusedtoreferenceitsmembers.

Whatistheuseof'using'declaration

Ausingdeclarationmakesitpossibletouseanamefromanamespacewithoutthescope范围operator.

WhatisanIterator迭代器class

Aclassthatisusedtotraversethrough穿过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悬挂pointer

Adanglingpointerariseswhenyouusetheaddressofanobjectafteritslifetimeisover.Thismayoccurinsituationslikereturningaddressesoftheautomaticvariablesfromafunctiono