C++编程思想 答案 第十一章 其他章节点击用户名找 thinking in C++ annotated solution guidecharpter 11Word文件下载.docx

C++编程思想 答案 第十一章 其他章节点击用户名找 thinking in C++ annotated solution guidecharpter 11Word文件下载.docx

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Writeaprograminwhichyoutryto

（1）Createareferencethatisnotinitializedwhenitiscreated.

（2）Changeareferencetorefertoanotherobjectafteritisinitialized.（3）CreateaNULLreference.

11-4

Writeafunctionthattakesapointerargument,modifieswhatthepointerpointsto,andthenreturnsthedestinationofthepointerasareference.

11-5

Createaclasswithsomememberfunctions,andmakethattheobjectthatispointedtobytheargumentofExercise4.Makethepointeraconstandmakesomeofthememberfunctionsconstandprovethatyoucanonlycalltheconstmemberfunctionsinsideyourfunction.Maketheargumenttoyourfunctionareferenceinsteadofapointer.

11-6

Takethecodefragmentsatthebeginningofthesectiontitled“Pointerreferences”andturnthemintoaprogram.

11-7

Createafunctionthattakesanargumentofareferencetoapointertoapointerandmodifiesthatargument.Inmain（）,callthefunction.

11-8

Createafunctionthattakesachar&

argumentandmodifiesthatargument.Inmain（）,printoutacharvariable,callyourfunctionforthatvariable,andprintitoutagaintoprovetoyourselfthatithasbeenchanged.Howdoesthisaffectprogramreadability?

Solution:

//:

S11:

CallByRef.cpp

#include<

iostream>

voidnextc（char&

c）{

staticcharletter='

a'

;

c=letter++;

}

intmain（）{

usingnamespacestd;

charc='

z'

cout<

<

"

c=="

<

c<

endl;

nextc（c）;

/*Output:

c==z

c==a

c==b

*/

///:

~

ACprogrammerwillfinditverystrangeindeedthatcischangedinmain（）,sinceapointerwasn’tpassed.Pass-by-referencesemanticshavesideeffectsandshouldbeusedsparingly.Agoodexampleisistream:

:

get（char&

c）.Sincestreamfunctionsreturnareferencetothestreamitselfsoyoucanimmediatelytestitforend-of-file,thecharacterextractedfromtheinputstreamisstoredviathereferenceargumentc.

11-9

Writeaclassthathasaconstmemberfunctionandanon-constmemberfunction.Writethreefunctionsthattakeanobjectofthatclassasanargument;

thefirsttakesitbyvalue,thesecondbyreference,andthethirdbyconstreference.Insidethefunctions,trytocallbothmemberfunctionsofyourclassandexplaintheresults.

11-10

（Somewhatchallenging）Writeasimplefunctionthattakesanintasanargument,incrementsthevalue,andreturnsit.Inmain（）,callyourfunction.Nowdiscoverhowyourcompilergeneratesassemblycodeandtracethroughtheassemblystatementssothatyouunderstandhowargumentsarepassedandreturned,andhowlocalvariablesareindexedoffthestack.

11-11

Writeafunctionthattakesasitsargumentsachar,int,float,anddouble.Generateassemblycodewithyourcompilerandfindthestatementsthatpushtheargumentsonthestackbeforeafunctioncall.

11-12

Writeafunctionthatreturnsadouble.Generateassemblycodeanddeterminehowthevalueisreturned.

11-13

ProduceassemblycodeforPassingBigStructures.cpp.Tracethroughanddemystifythewayyourcompilergeneratescodetopassandreturnlargestructures.

11-14

Writeasimplerecursivefunctionthatdecrementsitsargumentandreturnszeroiftheargumentbecomeszero,otherwiseitcallsitself.Generateassemblycodeforthisfunctionandexplainhowthewaythattheassemblycodeiscreatedbythecompilersupportsrecursion.

11-15

Writecodetoprovethatthecompilerautomaticallysynthesizesacopy-constructorifyoudon’tcreateoneyourself.Provethatthesynthesizedcopy-constructorperformsabitcopyofprimitivetypesandcallsthecopy-constructorofuser-definedtypes.

AutoCopy.cpp

usingnamespacestd;

classInner{

doublex;

public:

Inner（doublex）{

this->

x=x;

}

Inner（constInner&

i2）{

x=i2.x;

Inner:

Inner（constInner&

）\n"

doublegetX（）const{

returnx;

};

classOuter{

Innerm;

intn;

Outer（doublex,inti）:

m（x）,n（i）{}

voidprint（）{

'

（'

m.getX（）<

'

n<

Outero1（10.0,20）;

o1.print（）;

Outero2（o1）;

o2.print（）;

（10,20）

）

ClassOutercontainsaninstanceofclassInnerandanint,butithasnocopyconstructor,sothecompilerwillbuildoneforus.ClassInnerhasacopyconstructorthatannouncesitselfsoyoucanseethatitexecutes,andthesubsequentcalltoOuter:

print（）alsorevealsthattheintmemberwascopiedcorrectly.

11-16

Writeaclasswithacopy-constructorthatannouncesitselftocout.Nowcreateafunctionthatpassesanobjectofyournewclassinbyvalueandanotheronethatcreatesalocalobjectofyournewclassandreturnsitbyvalue.Callthesefunctionstoprovetoyourselfthatthecopy-constructorisindeedquietlycalledwhenpassingandreturningobjectsbyvalue.

TraceCopies.cpp

classTrace{

Trace（intn）{

Trace:

Trace（"

n=n;

Trace（constTrace&

t）{

Trace（constTrace&

n=t.n;

intgetN（）const{

returnn;

voidf（Tracet）{

f（"

t.getN（）<

Traceg（）{

Tracet

（2）;

returnt;

Traceh（intn）{

Tracet1=1;

f（t1）;

Tracet2=g（）;

Tracet3=h（3）;

*CompilerA:

Trace

（1）

f

（1）

Trace

（2）

Trace（3）

*CompilerB:

Simplydefineacopyconstructorthatannouncesitself.Rememberthatifyoudefineanyconstructoratall（includingacopyconstructor）,thecompilerwillnotsynthesizeadefaultconstructorforyou,soIneededtodefinesomeconstructorotherthanthecopyconstructorsoIcancreateTraceobjects.IchosetotakeanintargumentsoIcanbettertracethroughthehiddenoperations.

CompilerAperformsnooptimizationssoyoucanseeallthepossibleoperations.Thefirstlineisthecreationoft1,andthenexttwoarethecallthatpassest1tof（）.Thecalltog（）invokestwocallstothecopyconstructor:

onetocreatethereturnvalue,andanothertoinitializet2withthatvalue.Noticethath（）returnsaTraceobjectbyvalue,butinsteadofusingthecopyconstructoritusesthesingle-argconstructorthattakesanint.That’sbecausewe’reaskingthecompilertocreateaTraceobjectfromanint.Thebottomlineis,wheneveranobjectiscreated,someconstructoriscalled;

whichonedependsonthecontext.

CompilerBisalotsmarterthanCompilerAwhenitcomestocreatingcopies.

11-17

Createaclassthatcontainsadouble*.Theconstructorinitializesthedouble*bycallingnewdoubleandassigningavaluetotheresultingstoragefromtheconstructorargument.Thedestructorprintsthevaluethat’spointedto,assignsthatvalueto-1,callsdeleteforthestorage,andthensetsthepointertozero.Nowcreateafunctionthattakesanobjectofyourclassbyvalue,andcallthisfunctioninmain（）.Whathappens?

Fixtheproblembywritingacopy-constructor.

ShallowCopy.cpp

classHasPointer{

double*p;

HasPointer（doublex）{

p=newdouble（x）;

~HasPointer（）{

~HasPointer（）\n"

deletep;

*p<

voidf（HasPointerhp）

{

hp.print（）;

HasPointerhp（5）;

f（hp）;

5

~HasPointer（）

accessviolationerror...!

!

>

（Asasidenote,noticethatyoucanuseconstructorsyntaxtoinitializebuilt-intypesinnewexpressions,asintheconstructorforHasPointer.）

Whenyoucallf（hp）,acopyofhpispassedtof（）,thedestructorofwhichexecuteswhenthatcopyisnolongerneeded.Problemis,thedestructordeletesp,sowhenthedestructorrunsagaintodestroyhpasmain（）completes,ittriestodeletepasecondtime!

ThesolutionistohavethecompilerperformadeepcopyofHasPointerobjectsviaanappropriatecopyconstructor,suchas:

HasPointer（constHasPointer&

rhs）{

p=newdouble（*rhs.p）;

Asarule,aclasswithapointermemberprobablyneedsacopyconstructor（andasyou’llseeinthenextchapter,anappropriateassignmentoperatortoo）.

11-18

Createaclasswithaconstructorthatlookslikeacopy-construct