C++编程思想 答案 第八章 其他章节请点击用户名找 hinking in C++ annotated solution guidecharpter 8.docx

C++编程思想 答案 第八章 其他章节请点击用户名找 hinking in C++ annotated solution guidecharpter 8.docx

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C++编程思想答案第八章其他章节请点击用户名找hinkinginC++annotatedsolutionguidecharpter8

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AnnotatedSolutionGuide

Revision1.0

forThinkinginC++,2ndedition,Volume1

byChuckAllison

©2001MindView,Inc.AllRightsReserved.

[PreviousChapter][TableofContents][NextChapter]

Chapter8

8-1

Createthreeconstintvalues,thenaddthemtogethertoproduceavaluethatdeterminesthesizeofanarrayinanarraydefinition.TrytocompilethesamecodeinCandseewhathappens（youcangenerallyforceyourC++compilertorunasaCcompilerbyusingacommand-lineflag）.

（Lefttothereader）

8-2

ProvetoyourselfthattheCandC++compilersreallydotreatconstantsdifferently.Createaglobalconstanduseitinaglobalconstantexpression;thencompileitunderbothCandC++.

Solution:

//:

S08:

GlobalConst.cpp

constintn=100;

constintm=n+2;

intmain（）{

}///:

~

WhilethisisalegalC++program,Cdoesn’tallowexpressionswithconstvariablesatthegloballevel,sotheabovecodewillnotcompileinC.Ifyoumovethedeclarationofminsideofmain（）,however,itworksfineinC.Butdon’tletthismakeyouthinkthatyoucandothisforarraydeclarations.Exercise1showsthatyoucannotuseaconstvariableasanarraydimensioninCunderanycircumstances.

8-3

Createexampleconstdefinitionsforallthebuilt-intypesandtheirvariants.Usetheseinexpressionswithotherconststomakenewconstdefinitions.Makesuretheycompilesuccessfully.

（Lefttothereader）

8-4

Createaconstdefinitioninaheaderfile,includethatheaderfileintwo.cppfiles,thencompilethosefilesandlinkthem.Youshouldnotgetanyerrors.NowtrythesameexperimentwithC.

（Lefttothereader）

8-5

Createaconstwhosevalueisdeterminedatruntimebyreadingthetimewhentheprogramstarts（you’llhavetousethestandardheader）.Laterintheprogram,trytoreadasecondvalueofthetimeintoyourconstandseewhathappens.

Solution:

//:

S08:

ConstTime.cpp

#include

#include

usingnamespacestd;

consttime_tnow=time（0）;

intmain（）{

cout<（now）<

//now=time（0）;

//cout<（now）<

}

/*Output:

949180534

*/

///:

~

Thefirstcommentedlineisillegalbecauseyoucan’tassigntoconstvariables–theycanonlybeinitialized.ImadethevariablenowglobaltoemphasizeanimportantdifferencebetweenCandC++:

youcaninitializeautomaticvariablesatruntimeinC,butnotglobals,likeyoucaninC++.Forexample,thefollowingCprogramworksjustfine:

//:

S08:

ConstTime.c

#include

#include

intmain（）{

consttime_tnow=time（0）;

printf（"%ld",now）;

}

/*Output:

949180534

*/

///:

~

Ifyoumovethedefinitionofnowoutsideofmain（）,aCcompilerwillcomplain.

8-6

Createaconstarrayofchar,thentrytochangeoneofthechars.

（Lefttothereader）

8-7

Createanexternconstdeclarationinonefile,andputamain（）inthatfilethatprintsthevalueoftheexternconst.Provideanexternconstdefinitioninasecondfile,thencompileandlinkthetwofilestogether.

（Lefttothereader）

8-8

Writetwopointerstoconstlongusingbothformsofthedeclaration.Pointoneofthemtoanarrayoflong.Demonstratethatyoucanincrementordecrementthepointer,butyoucan’tchangewhatitpointsto.

（Lefttothereader）

8-9

Writeaconstpointertoadouble,andpointitatanarrayofdouble.Showthatyoucanchangewhatthepointerpointsto,butyoucan’tincrementordecrementthepointer.

（Lefttothereader）

8-10

Writeaconstpointertoaconstobject.Showthatyoucanonlyreadthevaluethatthepointerpointsto,butyoucan’tchangethepointerorwhatitpointsto.

（Lefttothereader）

8-11

Removethecommentontheerror-generatinglineofcodeinPointerAssignment.cpptoseetheerrorthatyourcompilergenerates.

（Lefttothereader）

8-12

Createacharacterarrayliteralwithapointerthatpointstothebeginningofthearray.Nowusethepointertomodifyelementsinthearray.Doesyourcompilerreportthisasanerror?

Shouldit?

Ifitdoesn’t,whydoyouthinkthatis?

Solution:

//:

S08:

StringLiteral.cpp

#include

intmain（）{

usingnamespacestd;

char*word="hello";

*word='j';

cout<

}

/*Output:

jello

*/

///:

~

Asexplainedinthebook,eventhoughstringliteralsarearraysofconstchar,forcompatibilitywithCyoucanassignthemtoachar*（“pointertoanon-constchar”）.You’renotsupposedtobeabletochangeastringliteral（thestandardsaysthatanysuchattempthasundefinedresults）,butmostcompilersruntheprogramabovethesame.It’scertainlynotarecommendpractice.

8-13

Createafunctionthattakesanargumentbyvalueasaconst;thentrytochangethatargumentinthefunctionbody.

（Lefttothereader）

8-14

Createafunctionthattakesafloatbyvalue.Insidethefunction,bindaconstfloat&totheargument,andonlyusethereferencefromthenontoensurethattheargumentisnotchanged.

（Lefttothereader）

8-15

ModifyConstReturnValues.cppremovingcommentsontheerror-causinglinesoneatatime,toseewhaterrormessagesyourcompilergenerates.

（Lefttothereader）

8-16

ModifyConstPointer.cppremovingcommentsontheerror-causinglinesoneatatime,toseewhaterrormessagesyourcompilergenerates.

（Lefttothereader）

8-17

MakeanewversionofConstPointer.cppcalledConstReference.cppwhichdemonstratesreferencesinsteadofpointers（youmayneedtolookforwardtoChapter11）.

Solution:

//:

S08:

ConstReference.cpp

//Constantreferencearg/return

voidt（int&）{}

voidu（constint&cir）{

inti=cir;

}

constint&w（）{

staticinti;

returni;

}

intmain（）{

intx=0;

int&ir=x;

constint&cir=x;

t（ir）;

//!

t（cir）;//NotOK

u（ir）;

u（cir）;

//!

int&ip2=w（）;//NotOK

constint&cir2=w（）;

//!

w（）=1;//NotOK

}///:

~

WhencomparingthisprogramtoConstPointer.cppinthebook,noticefirsttheomissionofthosestatementsthatqualifythereferenceitselfasconst.Whileyoucandeclareapointeritselftobeconst（asopposedtoapointer-to-const）,allreferencesareimplicitlyconst,becauseonceboundtoanobjectyoucan’tchangethatbinding（moreinChapter11）.Thecommented-outstatementsareallconstviolations（i.e.,youcan’tassignviaareference-to-const）.

8-18

ModifyConstTemporary.cppremovingthecommentontheerror-causinglinetoseewhaterrormessagesyourcompilergenerates.

（Lefttothereader）

8-19

Createaclasscontainingbothaconstandanon-constfloat.Initializetheseusingtheconstructorinitializerlist.

Solution:

//:

S08:

InitList.cpp

#include

usingnamespacestd;

classHasFloats{

constfloatx_;

floaty_;

public:

HasFloats（floatx,floaty）

:

x_（x）,y_（y）

{}

voiddisplay（）const{

cout<<"x=="<

}

};

intmain（）{

HasFloatsh（3,4）;

h.display（）;

}

/*Output:

x==3,y==4

*/

///:

~

Youcaninitializey_inthebodyoftheconstructorifyouwish,butconstmemberslikex_mustbeinitializedintheinitializerlist.

8-20

CreateaclasscalledMyStringwhichcontainsastringandhasaconstructorthatinitializesthestring,andaprint（）function.ModifyStringStack.cppsothatthecontainerholdsMyStringobjects,andmain（）soitprintsthem.

（Lefttothereader）

8-21

Createaclasscontainingaconstmemberthatyouinitializeintheconstructorinitializerlistandanuntaggedenumerationthatyouusetodetermineanarraysize.

（Lefttothereader）

8-22

InConstMember.cpp,removetheconstspecifieronthememberfunctiondefinition,butleaveitonthedeclaration,toseewhatkindofcompilererrormessageyouget.

（Lefttothereader）

8-23

Createaclasswithbothconstandnon-constmemberfunctions.Createconstandnon-constobjectsofthisclass,andtrycallingthedifferenttypesofmemberfunctionsforthedifferenttypesofobjects.

（Lefttothereader）

8-24

Createaclasswithbothconstandnon-constmemberfunctions.Trytocallanon-constmemberfunctionfromaconstmemberfunctiontoseewhatkindofcompilererrormessageyouget.

（Lefttothereader）

8-25

InMutable.cpp,removethecommentontheerror-causinglinetoseewhatsortoferrormessageyourcompilerproduces.

（Lefttothereader）

8-26

ModifyQuoter.cppbymakingquote（）aconstmemberfunctionandlastquotemutable.

Solution:

Here’sthemodifiedclassdefinition:

//:

S08:

Quoter.cpp{O}

#include

#include

#include

usingnamespacestd;

classQuoter{

mutableintlastquote;

public:

Quoter（）;

intlastQuote（）const;

constchar*quote（）const;

};///:

~

Don’tforgettoaddaconstsuffixtothedefinitionofQuoter:

:

quote（）also.Nootherchangesarenecessary.

8-27

Createaclasswithavolatiledatamember.Createbothvolatileandnon-volatilememberfunctionsthatmodifythevolatiledatamember,andseewhatthecompilersays.Createbothvolatileandnon-volatileobjectsofyourclassandtrycallingboththevolatileandnon-volatilememberfunctionstoseewhatissuccessfulandwhatkindoferrormessagesthecompilerproduces.

Solution:

//:

S08:

Volatile.cpp

classVolatile{

volatileintx;

public:

voidmod1（intx）{

this->x=x;

}

voidmod2（intx）volatile{

this->x=x;

}

};

intmain（）{

Volatilev1;

volatileVolatilev2;

v1.mod1

（1）;

v1.mod2

（2）;

//!

v2.mod1（3）;//Error

v2.mod2（4）;

}///:

~

Theonlyerrorisinattemptingtocallanon-volatilefunctionforavolatileobject.Youmightthinkthatmod1（