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 11.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 11.docx

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C++编程思想答案第十一章其他章节点击用户名找thinkinginC++annotatedsolutionguidecharpter11

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AnnotatedSolutionGuide

Revision1.0

forThinkinginC++,2ndedition,Volume1

byChuckAllison

©2001MindView,Inc.AllRightsReserved.

[PreviousChapter][TableofContents][NextChapter]

Chapter11

11-1

Turnthe“bird&rock”codefragmentatthebeginningofthischapterintoaCprogram（usingstructsforthedatatypes）,andshowthatitcompiles.NowtrytocompileitwiththeC++compilerandseewhathappens.

（Lefttothereader）

11-2

Takethecodefragmentsinthebeginningofthesectiontitled“ReferencesinC++”andputthemintoamain（）.Addstatementstoprintoutputsothatyoucanprovetoyourselfthatreferencesarelikepointersthatareautomaticallydereferenced.

（Lefttothereader）

11-3

Writeaprograminwhichyoutryto

（1）Createareferencethatisnotinitializedwhenitiscreated.

（2）Changeareferencetorefertoanotherobjectafteritisinitialized.（3）CreateaNULLreference.

（Lefttothereader）

11-4

Writeafunctionthattakesapointerargument,modifieswhatthepointerpointsto,andthenreturnsthedestinationofthepointerasareference.

（Lefttothereader）

11-5

Createaclasswithsomememberfunctions,andmakethattheobjectthatispointedtobytheargumentofExercise4.Makethepointeraconstandmakesomeofthememberfunctionsconstandprovethatyoucanonlycalltheconstmemberfunctionsinsideyourfunction.Maketheargumenttoyourfunctionareferenceinsteadofapointer.

（Lefttothereader）

11-6

Takethecodefragmentsatthebeginningofthesectiontitled“Pointerreferences”andturnthemintoaprogram.

（Lefttothereader）

11-7

Createafunctionthattakesanargumentofareferencetoapointertoapointerandmodifiesthatargument.Inmain（）,callthefunction.

（Lefttothereader）

11-8

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

Solution:

//:

S11:

CallByRef.cpp

#include

voidnextc（char&c）{

staticcharletter='a';

c=letter++;

}

intmain（）{

usingnamespacestd;

charc='z';

cout<<"c=="<

nextc（c）;

cout<<"c=="<

nextc（c）;

cout<<"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.

（Lefttothereader）

11-10

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

（Lefttothereader）

11-11

Writeafunctionthattakesasitsargumentsachar,int,float,anddouble.Generateassemblycodewithyourcompilerandfindthestatementsthatpushtheargumentsonthestackbeforeafunctioncall.

（Lefttothereader）

11-12

Writeafunctionthatreturnsadouble.Generateassemblycodeanddeterminehowthevalueisreturned.

（Lefttothereader）

11-13

ProduceassemblycodeforPassingBigStructures.cpp.Tracethroughanddemystifythewayyourcompilergeneratescodetopassandreturnlargestructures.

（Lefttothereader）

11-14

Writeasimplerecursivefunctionthatdecrementsitsargumentandreturnszeroiftheargumentbecomeszero,otherwiseitcallsitself.Generateassemblycodeforthisfunctionandexplainhowthewaythattheassemblycodeiscreatedbythecompilersupportsrecursion.

（Lefttothereader）

11-15

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

Solution:

//:

S11:

AutoCopy.cpp

#include

usingnamespacestd;

classInner{

doublex;

public:

Inner（doublex）{

this->x=x;

}

Inner（constInner&i2）{

x=i2.x;

cout<<"Inner:

:

Inner（constInner&）\n";

}

doublegetX（）const{

returnx;

}

};

classOuter{

Innerm;

intn;

public:

Outer（doublex,inti）:

m（x）,n（i）{}

voidprint（）{

cout<<'（'<

}

};

intmain（）{

Outero1（10.0,20）;

o1.print（）;

Outero2（o1）;

o2.print（）;

}

/*Output:

（10,20）

Inner:

:

Inner（constInner&）

（10,20）

*/

///:

~

ClassOutercontainsaninstanceofclassInnerandanint,butithasnocopyconstructor,sothecompilerwillbuildoneforus.ClassInnerhasacopyconstructorthatannouncesitselfsoyoucanseethatitexecutes,andthesubsequentcalltoOuter:

:

print（）alsorevealsthattheintmemberwascopiedcorrectly.

11-16

Writeaclasswithacopy-constructorthatannouncesitselftocout.Nowcreateafunctionthatpassesanobjectofyournewclassinbyvalueandanotheronethatcreatesalocalobjectofyournewclassandreturnsitbyvalue.Callthesefunctionstoprovetoyourselfthatthecopy-constructorisindeedquietlycalledwhenpassingandreturningobjectsbyvalue.

Solution:

//:

S11:

TraceCopies.cpp

#include

usingnamespacestd;

classTrace{

intn;

public:

Trace（intn）{

cout<<"Trace:

:

Trace（"<

this->n=n;

}

Trace（constTrace&t）{

cout<<"Trace:

:

Trace（constTrace&）\n";

n=t.n;

}

intgetN（）const{

returnn;

}

};

voidf（Tracet）{

cout<<"f（"<

}

Traceg（）{

Tracet

（2）;

returnt;

}

Traceh（intn）{

returnn;

}

intmain（）{

Tracet1=1;

f（t1）;

Tracet2=g（）;

Tracet3=h（3）;

}

/*Output:

*CompilerA:

Trace:

:

Trace

（1）

Trace:

:

Trace（constTrace&）

f

（1）

Trace:

:

Trace

（2）

Trace:

:

Trace（constTrace&）

Trace:

:

Trace（constTrace&）

Trace:

:

Trace（3）

Trace:

:

Trace（constTrace&）

*CompilerB:

Trace:

:

Trace

（1）

Trace:

:

Trace（constTrace&）

f

（1）

Trace:

:

Trace

（2）

Trace:

:

Trace（constTrace&）

Trace:

:

Trace（3）

*/

///:

~

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.

Solution:

//:

S11:

ShallowCopy.cpp

#include

usingnamespacestd;

classHasPointer{

double*p;

public:

HasPointer（doublex）{

p=newdouble（x）;

}

~HasPointer（）{

cout<<"~HasPointer（）\n";

deletep;

}

voidprint（）{

cout<<*p<

}

};

voidf（HasPointerhp）

{

hp.print（）;

}

intmain（）{

HasPointerhp（5）;

f（hp）;

}

/*Output:

5

~HasPointer（）

~HasPointer（）

!

!

>

*/

///:

~

（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