C++常见英文面试笔精彩试题.docx

C++常见英文面试笔精彩试题.docx

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C++常见英文面试笔精彩试题

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）;//callingBooconstructor

BooObj2（Obj1）;//callingboocopyconstructor

BooObj2=Obj1;//callingboocopyconstructor

Whenarecopyconstructorscalled?

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

i:

j）

template:

template

Tmin（Ti,Tj）

{

returni

i:

j;

}

WhatareC++storageclasses?

auto

register

static

extern

auto:

thedefault.Variablesareautomaticallycreatedandinitializedwhentheyaredefinedandaredestroyedattheendoftheblockcontainingtheirdefinition.Theyarenotvisibleoutsidethatblock

register:

atypeofautovariable.asuggestiontothecompilertouseaCPUregisterforperformance

static:

avariablethatisknownonlyinthefunctionthatcontainsitsdefinitionbutisneverdestroyedandretains=keepitsvaluebetweencallstothatfunction.Itexistsfromthetimetheprogrambeginsexecution

extern:

astaticvariablewhosedefinitionandplacementisdeterminedwhenallobjectandlibrarymodulesarecombined（linked）toformtheexecutablecodefile.Itcanbevisibleoutsidethefilewhereitisdefined.

WhatarestoragequalifiersinC++?

Theyare..

const

volatile

mutable

Constkeywordindicatesthatmemoryonceinitialized,shouldnotbealteredbyaprogram.

volatilekeywordindicatesthatthevalueinthememorylocationcanbealteredeventhoughnothingintheprogram

codemodifiesthecontents.forexampleifyouhaveapointertohardwarelocationthatcontainsthetime,wherehardwarechangesthevalueofthispointervariableandnottheprogram.Theintentofthiskeywordtoimprovetheoptimizationabilityofthecompiler.

mutablekeywordindicatesthatparticularmemberofastructureorclasscanbealteredevenifaparticularstructurevariable,class,orclassmemberfunctionisconstant.

structdata

{

charname[80];

mutabledoublesalary;

}

constdataMyStruct={"SatishShetty",1000};//initlizedbycomplier

strcpy（MyStruct.name,"ShilpaShetty"）;//compilererror

MyStruct.salaray=2000;//complierishappyallowed

Whatisreference?

?

referenceisanamethatactsasanalias,oralternativename,forapreviouslydefinedvariableoranobject.

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=2.0;

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

b）Theactualargumentisofthewrongtype,butofatypethatcanbeconvertedtothecorrecttype

longtemp=3L;

doublevalue=cuberoot（temp）;//longtodoubleconversion

Whatisvirtualfunction?

Whenderivedclassoverridesthebaseclassmethodbyredefiningthesamefunction,thenifclientwantstoaccessredefinedthemethodfromderivedclassthroughapointerfrombaseclassobject,thenyoumustdefinethisfunctioninbaseclassasvirtualfunction.

classparent

{

voidShow（）

{

cout<<"i'mparent"<

}

};

classchild:

publicparent

{

voidShow（）

{

cout<<"i'mchild"<

}

};

parent*parent_object_ptr=newchild;

parent_object_ptr->show（）//callsparent->show（）i

nowwegotovirtualworld...

classparent

{

virtualvoidShow（）

{

cout<<"i'mparent"<

}

};

classchild:

publicparent

{

voidShow（）

{

cout<<"i'mchild"<

}

};

parent*parent_object_ptr=newchild;

parent_object_ptr->show（）//callschild->show（）

Whatispurevirtualfunction?

orwhatisabstractclass?

Whenyoudefineonlyfunctionprototypeinabaseclasswithoutimplementationanddothecompleteimplementation实现inderivedclass.Thisbaseclassiscalledabstractclassandclientwon'tabletoinstantiateanobjectusingthisbaseclass.

Youcanmakeapurevirtualfunctionorabstractclassthisway..

classBoo

{

voidfoo（）=0;

}

BooMyBoo;//compilationerror

WhatisMemoryalignment?

?

Thetermalignmentprimarilymeansthetendency趋向ofanaddresspointerva