C++编程思想 答案 第七章 其他章节请点击用户名找 thinking in C++ annotated solution guidecharpter 7Word格式文档下载.docx

C++编程思想 答案 第七章 其他章节请点击用户名找 thinking in C++ annotated solution guidecharpter 7Word格式文档下载.docx

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Text.cpp

#include<

iostream>

fstream>

string>

usingnamespacestd;

classText{

stringtext;

public:

Text（）{}

Text（conststring&

fname）{

ifstreamifs（fname.c_str（））;

stringline;

while（getline（ifs,line））

text+=line+'

\n'

;

}

stringcontents（）{

returntext;

};

intmain（intargc,char*argv[]）{

if（argc>

1）

{

Textt1;

Textt2（argv[1]）;

cout<

<

"

t1:

\n"

<

t1.contents（）<

endl;

t2:

t2.contents（）<

}

///:

~

WhencreatingaTextobject,thecompilerguaranteesthatthetextdatamemberhasitsdefaultconstructor（string:

:

string（））executedbeforeeitherTextconstructorruns,hencethedefaultTextconstructorjustbuildsanemptystring.Thisprogramprintsanemptystringfort1followedbythecontentsofthefilenamedinthefirstcommand-lineargument.Notetheuseofstring:

c_str（）inthesecondconstructor.That’sbecausetheifstreamconstructortakesachar*argument,notastring.

7-2

CreateaMessageclasswithaconstructorthattakesasinglestringwithadefaultvalue.Createaprivatememberstring,andintheconstructorsimplyassigntheargumentstringtoyourinternalstring.Createtwooverloadedmemberfunctionscalledprint（）:

onethattakesnoargumentsandsimplyprintsthemessagestoredintheobject,andonethattakesastringargument,whichitprintsinadditiontotheinternalmessage.Doesitmakesensetousethisapproachinsteadoftheoneusedfortheconstructor?

Message.cpp

classMessage{

stringmsg;

Message（conststring&

s="

MSG"

）:

msg（s）{}

voidprint（）{

msg<

voidprint（conststring&

suffix）{

'

suffix<

intmain（）{

Messagem1;

Messagem2（"

Error"

）;

m1.print（）;

m2.print（）;

m1.print（"

hello"

m2.print（"

goodbye"

/*Output:

MSG

Error

MSGhello

Errorgoodbye

*/

It’susuallymoreflexibletoallowoptionalargumentsinthecalltoprint,sincethetextofamessageisfixedwhenitiscreated.Acommontechniqueallowsanoptionalprefixformessages,asthefollowingexampleillustrates.

MessageWithPrefix.cpp

s）:

prefix）{

prefix<

Messagem（"

Thisisamessage"

m.print（）;

m.print（"

Attention"

Thisisamessage

Attention:

Thisisamessage

7-3

Determinehowtogenerateassemblyoutputwithyourcompiler,andrunexperimentstodeducethename-decorationscheme.

（Lefttothereader）

7-4

Createaclassthatcontainsfourmemberfunctions,with0,1,2,and3intarguments,respectively.Createamain（）thatmakesanobjectofyourclassandcallseachofthememberfunctions.Nowmodifytheclasssoithasinsteadasinglememberfunctionwithalltheargumentsdefaulted.Doesthischangeyourmain（）?

Here’sthefirstversion:

ManyArgs.cpp

classManyArgs{

voidf（）{

{}\n"

voidf（inti）{

{"

i<

}\n"

voidf（inti,intj）{

"

j<

voidf（inti,intj,intk）{

k<

ManyArgsa;

a.f（）;

a.f

（1）;

a.f（1,2）;

a.f（1,2,3）;

{}

{1}

{1,2}

{1,2,3}

Nowcomparetheoutputabovetothatfromthisdefault-argumentversion:

DefaultArgs.cpp

classDefaultArgs{

voidf（inti=0,intj=0,intk=0）{

DefaultArgsa;

{0,0,0}

{1,0,0}

{1,2,0}

Althoughit’struethattheoperationsinmain（）didnotchange,therespectiveoutputssuggestwheneachfeatureisappropriate.Usedefaultargumentswhentheretrulyisadefaultvalue（likezeroabove）.Whenyouwantnovalueatallincertaininstances,thenthefunctionsaredifferentenoughthatyouneedtheoverloads.

7-5

Createafunctionwithtwoargumentsandcallitfrommain（）.Nowmakeoneoftheargumentsa“placeholder”（noidentifier）andseeifyourcallinmain（）changes.

NamelessArg.cpp

voidtwoArgs（inti,floatx）{

twoArgs（"

x<

）\n"

voidplaceHolder（inti,float）{

）\n"

twoArgs（1,2）;

placeHolder（1,2）;

twoArgs（1,2）

twoArgs（1,）

Placeholdersareusefulinthoserareoccasions（ofteninmaintainingcode）whenyouneeddifferentversionsofafunction,butonlythetype,notthevalue,ofthedifferentiatingparameterisimportant.

（Exercises6–10lefttothereader）

7-6

ModifyStash3.handStash3.cpptousedefaultargumentsintheconstructor.TesttheconstructorbymakingtwodifferentversionsofaStashobject.

7-7

CreateanewversionoftheStackclass（fromChapter6）thatcontainsthedefaultconstructorasbefore,andasecondconstructorthattakesasitsargumentsanarrayofpointerstoobjectsandthesizeofthatarray.ThisconstructorshouldmovethroughthearrayandpusheachpointerontotheStack.Testyourclasswithanarrayofstring.

7-8

ModifySuperVarsothatthereare#ifdefsaroundallthevartypecodeasdescribedinthesectiononenum.Makevartypearegularandpublicenumeration（withnoinstance）andmodifyprint（）sothatitrequiresavartypeargumenttotellitwhattodo.

7-9

ImplementMem2.handmakesurethatthemodifiedclassstillworkswithMemTest.cpp.

7-10

UseclassMemtoimplementStash.Notethatbecausetheimplementationisprivateandthushiddenfromtheclientprogrammer,thetestcodedoesnotneedtobemodified.

InclassMem,addaboolmoved（）memberfunctionthattakestheresultofacalltopointer（）andtellsyouwhetherthepointerhasmoved（duetoreallocation）.Writeamain（）thattestsyourmoved（）memberfunction.Doesitmakemoresensetousesomethinglikemoved（）ortosimplycallpointer（）everytimeyouneedtoaccessthememoryinMem?

LastUpdate:

06/27/2002