Ch_05_IO_Streams_as_an_Introduction_to_Objects_and_Classes.ppt

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1、Chapter5I/OStreamsasanIntroductiontoObjectsandClassesCopyright©2008PEARSONEDUCATIONASIALIMITEDandTsinghuaUniversityPressOverview5.1StreamsandBasicFileI/O5.2ToolsforStreamI/O5.3CharacterI/O5.4Inheritance5.5RandomAccesstoFiles(Optional)25.1StreamsandBasicFileI/OCopyright©2008PEARSONEDUCATI

2、ONASIALIMITEDandTsinghuaUniversityPressI/OStreamsI/OreferstoprograminputandoutputInputisdeliveredtoyourprogramviaastreamobjectInputcanbefromThekeyboardAfileOutputisdeliveredtotheoutputdeviceviaastreamobjectOutputcanbetoThescreenAfile4ObjectsObjectsarespecialvariablesthatHavetheirownspec

3、ial-purposefunctionsSetC++apartfromearlierprogramminglanguages5StreamsandBasicFileI/OFilesforI/OarethesametypeoffilesusedtostoreprogramsAstreamisaflowofdata.Inputstream:DataflowsintotheprogramIfinputstreamflowsfromkeyboard,theprogramwillacceptdatafromthekeyboardIfinputstreamflowsfromaf

4、ile,theprogramwillacceptdatafromthefileOutputstream:DataflowsoutoftheprogramTothescreenToafile6cinAndcoutStreamscinInputstreamconnectedtothekeyboardcoutOutputstreamconnectedtothescreencinandcoutdefinedintheiostreamlibraryUseincludedirective:#includeYoucandeclareyourownstreamst

5、ousewithfiles.7WhyUseFiles?Filesallowyoutostoredatapermanently!DataoutputtoafilelastsaftertheprogramendsAninputfilecanbeusedoverandoverNotypingofdataagainandagainfortestingCreateadatafileorreadanoutputfileatyourconvenienceFilesallowyoutodealwithlargerdatasets8FileI/OReadingfromafileTak

6、inginputfromafileDonefrombeginningtotheend(fornow)Nobackinguptoreadsomethingagain(OKtostartover)JustasdonefromthekeyboardWritingtoafileSendingoutputtoafileDonefrombeginningtoend(fornow)Nobackinguptowritesomethingagain(OKtostartover)Justasdonetothescreen9StreamVariablesLikeothervariables,

7、astreamvariable…MustbedeclaredbeforeitcanbeusedMustbeinitializedbeforeitcontainsvaliddataInitializingastreammeansconnectingittoafileThevalueofthestreamvariablecanbethoughtofasthefileitisconnectedtoCanhaveitsvaluechangedChangingastreamvaluemeansdisconnectingfromonefileand