C++InterviewQuestion.docx

C++InterviewQuestion.docx

《C++InterviewQuestion.docx》由会员分享，可在线阅读，更多相关《C++InterviewQuestion.docx（12页珍藏版）》请在冰豆网上搜索。

C++InterviewQuestion

C++InterviewQuestions

Name:

ZhuoDu

1.Howdoyoudecidewhichintegertypetouse?

Itdependsonourrequirement.Whenwearerequiredanintegertobestoredin1byte（meanslessthanorequalto255）weuseshortint,for2bytesweuseint,for8bytesweuselongint.Acharisfor1-byteintegers,ashortisfor2-byteintegers,anintisgenerallya2-byteor4-byteinteger（thoughnotnecessarily）,alongisa4-byteinteger,andalonglongisa8-byteinteger.

2.Whatdoesexternmeaninafunctiondeclaration?

Anexternfunctionoramembercanbeaccessedoutsidethescopeofthe.cppfileinwhichitwasdefined.

3.What’stheautokeywordgoodfor?

 Itdeclaresanobjectwithautomaticstorageduration.Whichmeanstheobjectwillbedestroyedattheendoftheobjectsscope.Allvariablesinfunctionsthatarenotdeclaredasstaticandnotdynamicallyallocatedhaveautomaticstoragedurationbydefault.

4.Definealinkedlistnodewhichcontainsapointertoitself.

#include

intmain（）{

void*ptr;

ptr=&ptr;

return0;

}

5.HowdoIdeclareanarrayofNpointerstofunctionsreturningpointerstofunctionsreturningpointerstocharacters?

Ifyouwantthecodetobeevenslightlyreadable,youwillusetypedefs.

typedefchar*（*functiontype_one）（void）;

typedeffunctiontype_one（*functiontype_two）（void）;

functiontype_twomyarray[N];//assumingNisaconstintegral

char*（*（*a[N]）（））（）;

6.HowcanIdeclareafunctionthatreturnsapointertoafunctionofitsowntype?

some_typef（）

{

staticintcnt=1;

std:

:

cout<

:

endl;

}

intmain（）

{

f（）（）（）...（）;//ncalls

}

7.WhatcanIsafelyassumeabouttheinitialvaluesofvariableswhicharenotexplicitlyinitialized?

Itdependsoncomplierwhichmayassignanygarbagevaluetoavariableifitisnotinitialized.

8.HowcanIcreateatwo-dimensionaldynamicarray?

Adynamic2Darrayisbasicallyanarrayof pointerstoarrays.Weshouldinitializeitusingaloop,likethis:

int**ary=newint*[rowCount];

for（inti=0;i

ary[i]=newint[colCount];

9.HowcanIdeallocateatwo-dimensionaldynamicarray?

Codetodeallocatethedynamicallyallocated2Darrayusingdeleteoperatorisasfollows,

voiddestroyTwoDimenArrayOnHeapUsingDelete（int**ptr,introw,intcol）

{

for（inti=0;i

delete[]ptr[i];

}

delete[]ptr;

}

10.Whatisavirtualfunction?

A virtualfunction isamember function thatyouexpecttoberedefinedinderivedclasses.Whenyourefertoaderivedclassobjectusingapointerorareferencetothebaseclass,youcancalla virtualfunctionforthatobjectandexecutethederivedclass'sversionofthe function.

11.HowdoIdodynamicbinding?

DynamicBinding:

thedecisionismadeatrun-timebaseduponthetypeoftheactualobject.CheckedVector:

:

operator[]willbecalledinthiscaseas（*vp->vptr[1]）（vp,0）.

Usewhenthederivedclassesmaybeabletoprovideadifferent（e.g.,morefunctional,moreefficient）implementationthatshouldbeselectedatrun-timeUsedtobuilddynamictypehierarchies&toform“abstractdatatypes”C

12.WhenshouldIusealocalstaticvariableinafunction?

a staticvariable isa variable thathasbeen allocatedstatically—whose lifetime or"extent"extendsacrosstheentirerunoftheprogram. 

13.WhenshouldIuse“register”todeclareavariable?

Usingregisterkeyword,youareinstructingthecompilertosavethecurrentdataintheregistermemoryoftheprocessor.Dataintheregistercanbefetchedquicklybytheprocessorbecauseofthelocalityofdata.Thedataiswiththeprocessor.Fetchingdatafromsecondarymemory（e.g.Harddisk）ormainmemory（RAM）requiresinstructioncycles. 

Butregistermemoryislimited!

!

ItsnegligibleifyouwillcompareitwiththeamountyoucanhaveonRAMorHardDisks. 

14.CanIputafunctionintoastruct?

Yes,a struct isidenticaltoa class exceptforthedefaultaccesslevel（member-wiseandinheritance-wise）.（andtheextrameaning class carrieswhenusedwithatemplate）

15.HowdoIinitializeapointertoafunction?

classFoo{

private:

staticdouble（*my_ptr_fun）（double,double）;

};

doublebar（double,double）;

double（*Foo:

:

my_ptr_fun）（double,double）=&bar;

Whateveryouwouldneedastaticfunctionpointerforanyway.

Thisiscalled initialization. instantiation meanssomethingdifferentinC++.

16.Arearraysrow-majororcolumn-major?

row-major

17.Whatisthedifferencebetweenanormalpointerandavoidpointer?

Genericpointeroftype 'void*' iscompatiblewithany（data-）pointer,butyoucannotusethefollowingoperatorsonit:

+-++--+=-=*->[]

18.Whatwillthefollowingprogramdo?

voidmain（）

{

inti;

chara[]="String";

char*p="NewSring";

char*Temp;

Temp=a;

a=malloc（strlen（p）+1）;

strcpy（a,p）;//Linenumber:

9//

p=malloc（strlen（Temp）+1）;

strcpy（p,Temp）;

printf（"（%s,%s）",a,p）;

free（p）;

free（a）;

}//Linenumber15//

a）Swapcontentsofp&aandprint:

（Newstring,string）

b）Generatecompilationerrorinlinenumber8

c）Generatecompilationerrorinlinenumber5

d）Generatecompilationerrorinlinenumber7

e）Generatecompilationerrorinlinenumber1

b）

19.enumnumber{a=-1,b=4,c,d,e};

Whatisthevalueofe?

（a）7

（b）4

（c）5

（d）15

（e）3

（d）15

20.Whatisthedifferencebetweenoverloadingandoverriding?

Themostbasic difference isthat overloading isbeingdoneinthesameclasswhilefor overriding baseandchildclassesarerequired.Overriding isallaboutgivingaspecificimplementationtotheinheritedmethodofparentclass.

21.Whatisthedifferencebetweenprivateandprotectedaccess?

Privatevariables,arevariablesthatarevisibleonlytotheclasstowhichtheybelong.

Protectedvariables,arevariablesthatarevisibleonlytotheclasstowhichtheybelong,andanysubclasses.

22.Whenarecopyconstructorscalled?

1.Whenanobjectoftheclassisreturnedbyvalue.

2.Whenanobjectoftheclassispassed（toafunction）byvalueasanargument.

3.Whenanobjectisconstructedbasedonanotherobjectofthesameclass.

4.Whencompilergeneratesatemporaryobject.

Itishowever,notguaranteedthatacopyconstructorwillbecalledinallthesecases,becausetheC++Standardallowsthecompilertooptimizethecopyawayincertaincases,oneexamplebeingthe returnvalueoptimization（sometimesreferredtoasRVO）.

23.Whatisdifferencebetweenmalloc（）/free（）andnew/delete?

24.HowdoIoverloadanassignmentoperator?

youcanoverloadtheassignmentoperator（=）justasyoucanotheroperatorsanditcanbeusedtocreateanobjectjustlikethecopyconstructor.

Followingexampleexplainshowanassignmentoperatorcanbeoverloaded.

#include

usingnamespacestd;

classDistance

{

private:

intfeet;//0toinfinite

intinches;//0to12

public:

//requiredconstructors

Distance（）{

feet=0;

inches=0;

}

Distance（intf,inti）{

feet=f;

inches=i;

}

voidoperator=（constDistance&D）

{

feet=D.feet;

inches=D.inches;

}

//methodtodisplaydistance

voiddisplayDistance（）

{

cout<<"F:

"<

"<

}

};

intmain（）

{

DistanceD1（11,10）,D2（5,11）;

cout<<"FirstDistance:

";

D1.displayDistance（）;

cout<<"SecondDistance:

";

D2.displayDistance（）;

//useassignmentoperator

D1=D2;

cout<<"FirstDistance:

";

D1.displayDistance（）;

return0;

}

25.Whatisspecialtostaticdatamembersandmemberfunctionsinaclass?

Aconstructorisaspecialmemberfunctionthatiscalledwheneveranewinstanceofaclassiscreated.Thecompilercallstheconstructorafterthenewobjecthasbeenallocatedinmemory,andconvertsthat"raw"memoryintoaproper,typedobject.Theconstructorisdeclaredmuchlikeanormalmemberfunctionbutitwillsharethenameoftheclassandithasnoreturnvalue.

26.whatisthedifferencebetween"new"and"operatornew"?

operatornew isthelowestlevelallocationmechanism.Actualobjectsshouldbeallocatedwith new,whichtellsC++toactuallycreatetheobjectandsetupallitsnecessaryplumbing（superclassinformation,vtables,etc.）,withoutwhichitisn'tcapableof being anobject.

27.Whatisthepurposeofkeyword“volatile”?

olatileisahinttotheimplementationto avoidaggressiveoptimizationinvolvingtheobjectbecausethevalueoftheobjectmightbechangedbymeansundetectablebyanimplementation.

28.Whatisthepurposeofkeyword“mutable”?

Itallowsthedifferentiationofbitwiseconstandlogicalconst.Logicalconstiswhenanobjectdoesn'tchangeinawaythatisvisiblethroughthepublicinterface,likeyourlockingexample.Anotherexamplewouldbeaclassthatcomputesavaluethefirsttimeitisrequested,andcachestheresult.

29.Whatispurevirtualfunction?

orwhatisabstractclass?

bstractClassisaclasswhichcontainsatleastonePureVirtualfunctioninit.AbstractclassesareusedtoprovideanInterfaceforitssubclasses.ClassesinheritinganAbstractClassmustprovidedefinitiontothepurevirtualfunction,otherwisetheywillalsobecomeabstractclass.

30.Canacopyconstructoracceptanobjectofthesameclassasparameter,insteadofreferenceoftheobject?

No.Itisspecifiedinthedefinitionofthecopyconstructoritself.Itshouldgenerateanerrorifaprogrammerspecifiesacopyconstructorwithafirstargumentthatisanobjectandnotareference.

31.Whatisalocalclass?

Whycanitbeuseful?

localclassisaclassdefinedwithinthescopeofafunction--anyfunction,whetheramemberfunctionorafreefunction.

Likenestedclasses,localclassesc