C语言程序设计课件英文Cprogramla

ChapterSevenFileChapterSevenFile1Contents

Introduction1Open/closefile2Read/writefile

3

Checkthestateoftheopeningfile4Thelocationofthefilepointer54hapterSevenContentsIntroduction1Open/clo2Howtogetthedatawhilerunaprogram?Wherewilltheresultin?Howcaninputtheresultofaprogramtoanotherprogram?

Introduction

TheprocedureofClanguageEditLinkCreatetheprogramtextCompileCompileitsuccessfullyLinkittotheCfunctionlibrary

hapterSevenHowtogetthedatawhilerun3

Introductionprogram

formatoutputcharacteroutputstringoutputinitializationassignmentinputfromkeyboardmemorymemoryformatinputcharacterinputstringinputQuestionReaddatafromafileWritedatatoafilehapterSevenIntroductionprogramformato4

Introduction

Fileisthegatherofrelatedinformationsavedinmemorydevice(assistantmemory)

OSmanagessysteminfiles

Processingfilesmeansfileinput/outprocessing.Procedure1openfile2fileread/write3closefile.Interfaceinput/outdevicesaretreatedasfilesinC.Fileaccessingmethods:

1)BufferedI/O(orstreamI/O)2)UnbufferedI/O(orlow-levelI/O)hapterSevenIntroductionFileisth5

IntroductionBuffered(temporarystoragelocation)

We’lldiscussBufferedI/OinourlectureInbufferedI/O,---openacommunicationareainRAMDISkPROGRAMOutputfilebuffer

InputfilebufferTherearetwowaystodealwithfile:BinaryfileASCIIfilestreamhapterSevenIntroductionBuffered6

IntroductionstreamStreamistheabstractoffileusedtodealwithfile.TherearetwokindsofstreamsinC.ThecharacterisASCIIcode.oneASCIIcodeoccupiesonebyte,newline‘\n’isendofline.Afterread/writeacharacterfrom/toASCIIfile,thefpincreasesautomaticallytoguaranteetheread/writesequences.TextstreamBinarystreamStoringdatatodiskintheformthesameasinRAM.Example:10000Inbinaryfile,use2bytesInASCIIfile,use5byteshapterSevenIntroductionstreamStreamis7Open/closefileHowtomagangeafileinC?PointerOperationsopenfile（loadfile）operatefileusingfunctionsclosefile（removefilefrommemory）BDFACEAfilesystemcreatanewfiledeleteanoldoneread/write

accessafilebyitsnamemanagethememoryfileusedlimittheuser’srighthapterSevenOpen/closefileHowtomagange8Open/closefile

Filepointer,pointstoastructurethatcontainsinformationaboutthefile,suchasthelocationofabuffer,thecurrentcharacterpositioninthebuffer,whetherthefileisbeingreadorwritten,andwhethererrorsorendoffilehaveoccurred.Usersdon’tneedtoknowthedetails,becausethedefinitionsobtainedfrom<stdio.h>includeastructuredeclarationcalledFILE.

AboutfilepointerIamastudent.hapterSevenOpen/closefileFilepo9

2Thefunctionofopeningafile:FILE*fp;

uppercaseletters,otherwise,can’tberecognized,

definedtostandardstructure,key--word

#include<stdio.h>isnecessary

fopen(filename,*mode);stringchararraycharpointerpathsareallowed

1filespointer:openingafileusefunctionfopen()

readwriteappend……Open/closefilehapterSeven2Thefunctionofopeninga10Open/closefilefp=fopen(“file.txt”,“r”);openfile.txt,readinASCIIOpeningafilemeans….returnsafilepointerspecifytheoperationtobedone

definingafilenamefirst……pointstothefirstlocationoffilebuffer.r----readfile.txtwhichThereturnedvalueisassignedtoafilepointer.hapterSevenOpen/closefilefp=fopen(“fil11

Ifprocessissuccessful,thereturnedvalueisafilepointer.(address)FLIE*fp;Otherwise,returnNULLpointer.if((fp=fopen(“file.txt”“r”)==NULL)){printf(“can’topenfile\n”);exist(1);}Open/closefileSymbolExplanationrreadwwriteaappendtTextstreambBinarystream+Permitread/write

Iffopenfails,returnvalueiszero(NULLpointer)when:

1)fopenwantstoopenanonexistedfileforreading.2)readafilenotpermittedread.3)createafilebutdiskisfull.

4)disksectorisbad.hapterSevenIfprocessissuccessful,th123CloseafileCloseafileopened,argument&apointertofiletobeclosedinorderto1)releasefpand2)cleanupthebuffer.fclose(fp);Open/closefile

Openedfilemustbeclosedbeforeendingaprogram,otherwise,datamaybelost.hapterSeven3CloseafileCloseafileope13

Writesstringintofilepointedbystream

Fileread/writefgets(string,n,stream)

Readsastringofupton-1charactersfromstreamandplacesthemintostringfputs(string,stream)

1read/writefilefunctionsfgetc(fp),fputc(fp)

read/writeacharfrom/tofileread:c=fgetc(fp);readacharfromnamedfile.write:fputc(c,fp);writectonamedfile.Prototypeinstdio.hreturnEOF(-1)ifa)attheendoffile;b)detectinganerror;Usingfunctionfgets()andfputs()canrealizestringinput/ouputinfiles.hapterSevenWritesstringintofilepoi14

main(intargc,char*argv[]){intc;FILE*fpr,*fpd;if(argc!=3) {putchar('\007');puts("Usage:copyfile1,file2"); exit();} if((fpr=fopen(argv[1],"r"))==NULL) {printf("%c",'\007');printf("file%scan'topen\n",argv[1]); exit();} if((fpd=fopen(argv[2],"w"))==NULL) {printf("\files%scan'topen\n",argv[2]); exit();}while((c=fgetc(fpr))!=EOF)fputc(c,fpd);fclose(fpr);fclose(fpd);}Inputthreestrings(filename)Sourcefilenameobjectfilename

Thefunctionofthisprogramistocopyfile1tofile2hapterSevenmain(intargc,char15#include<stdio.h>main(){FILE*fp;charc1；fp=fopen(“file.dat”,”r”)；

c1=fgetc(fp);putchar(c1);fclose(fp);}#include<stdio.h>main(){FILE*fp;charch=‘a’;fp=fopen(“file.dat”,”w”);fputc(ch,fp);fclose(fp);}Readthecharacterfromfile.dat

writecharacter‘a’tofile.dat.

Fileread/writefscanf(stream,format,arg,...)

Readsdatafromstreamusingformatconversionspecifierintoaddressspecifierdbyarg.fprintf(stream,format,arg,...)

Writesargintostreamusingformatconversionspecifier.hapterSeven#include<stdio.h>#include<stdi16main(){FILE*fp;char*c1=“TurboC”;charc2[10];fp=fopen(“file2.dat”,”w”);

fputs(c1,fp);

fclose(fp);fp=fopen(“file2.dat”,”r”);

fgets(c2,8,fp);printf(“%s\n”,c2);fclose(fp);}

Fileread/write

readastringfromdeterminedfile(fp),haveread7chars;Returnedvalue:normalthe1stlocationofthestring;errororendoffileNULLwriteastringtodeterminedfile(fp)Returnedvalue:normal:thenumberofchars;error:NULLhapterSevenmain()Fileread/writeread17main(){FILE*fp;char*c1=“TurboC”;charc2[10];fp=fopen(“file3.dat”,”w”);fprintf(fp,”%s”,c1);fclose(fp);fp=fopen(“file3.dat”,”r”);fscanf(fp,”%s”,c2);printf(“%s\n”,c2);fclose(fp);}

Fileread/writeItissimilartoprintf,addfp–filepointerItissimilartoscanf,addfp–filepointerhapterSevenmain()Fileread/writeItiss18main(){FILE*fp;charstr[81],filename[80];gets(filename);if((fp=fopen(filename,”w”))==NULL){printf(“cannotopenthisfile\n”);exit(0);}while(strlen(gets(str))>0){fputs(str,fp);fputs(“\n”,fp);}fclose(fp);}Inputseveralstrings,thensavethemtodiskCanyouuse“filename”here?Howmanystringsshouldyouinput??

Fileread/writehapterSevenmain()Inputseveralstrings,19freadreadsnitemsofsizelengthfromstreamintobuffer.

Fileread/write

fwrite()/fread()*Twostandardlibraryfunctionsareavailabletofacilitatethestorageofdataarraysinbinaryforms.Thesearefwrite()andfread().fwrite(buffer,size,n,stream);fread(buffer,size,n,stream);

buffer:apointertothestartofthebuffertobewrittenintostream.

n:itemsinthebufferoflengthsizeinbytes.hapterSevenfreadreadsnitemsofsizele20

whencomputerarestarted,3standardfilesareopenedautomatically,and3associatedfilepointersareprovided。Userneedn'twritestatementstoopenstandardfilesandafterprogramareexecuted,standardfilesautomaticallyclosed.2Interfaceinput/outdevicesstdinfileinputstdoutstandardoutputpointerstderrerror

exit(1):returntoos.Innormalexistexit(0):---normalexist.3Exitfunctionsprogramwillstoprightaway.

Fileread/writehapterSevenwhencomputerares21Thefile’sstateisnecessarywhenusinginput/outfunctions,especiallytestingtheendofafile.Thereareonecoupleofwaystotesttheendoffile1EOF

Whenreading/writingASCIIfile,EOFisusedtotestifthefilepointerpointstotheendoffile,ifso,thevalueofEOFis-1Can’tsuitforbinaryfile2functionfeof()

feof(filepointername)

Thereturnvalueisnonzeroattheendoffile,Otherwise,itisnottheendoffile.CheckthestateoftheopeningfilehapterSevenThefile’sstateisnecessary22while(feof(fp)==0)c=fgetc(fp);Checkthestateoftheopeningfilewhile((c=fgetc(fp)!=EOF))

putchar(c);Example:readcharactersfromafilehapterSevenwhile(feof(fp)==0)Checkthe23Thelocationofhefilepointer1rewind

rewind(filepointername）

Setsfilepointertostreamtobeginningoffile2fseek

Locatesfilepointerforstreamatoffsetbytesfromorigins

fseek(filepointername，offsets，origin）

Noreturnvalue

GenerallyitisUsedforbinaryfile0:thebegining1:currentposition2:theend

Thenumberofbytes+movebackwards-moveforwards

return:azeroifthepointerwasresetwithouterror.hapterSevenThelocationofhefilepointe243、Thecurrentposition

ftell(filepointername）

Returnscurrentpositionoffilepointedfromstream

Return1LmeansthereissomethingwrongThelocationofthefilepointerWhereisthecurrentpositionofthefilepointer?

0Beginningoffile1Currentpositionoffilepointer2Endoffile

fseek(filepointername，distance，origin）hapterSeven3、Thecurrentpositionftell25main(intargc,char*argv[]) {chars[80];inta; FILE*fp; if((fp=fopen("test","w"))==NULL) {printf("can'topenfile"); exit();} fscanf(stdin,"%s%d",s,&a);/*readfromkeyboard*/ fprintf(fp,"%s%d",s,a);/*writetofile*/ fclose(fp);if((fp=fopen("test","r"))==NULL) {printf("can'topenfile"); exit();}fscanf(fp,"%s%d",s,&a);/*readfromfile*/ fprintf(stdout,"%s%d",s,a);/*printonscreen*/ fclose(fp);}ThelocationofthefilepointerhapterSevenmain(intargc,char*argv[]26

/*WritinganarrayofdatausingfwriteFWRITE.C*/#include<stdio.h>main(){staticintbuffer[]={70,71,72,73,74,75,76,77,78,79,80,81,82,83};FILE*fp;inti;fp=fopen("testdata","w");fwrite((char*)buffer,2,14,fp);fclose(fp);}ThelocationofthefilepointerhapterSeven/*Writinganarrayofdata27

/*fread.c*/#include<stdio.h>main(){FILE*fp;staticintbuffer[14];inti;

fp=fopen("testdata","r");fread((char*)buffer,2,14,fp);fclose(fp);for(i=0;i<14;i++) printf("%d\n",buffer[i]);}ThelocationofthefilepointerhapterSeven/*fread.c*/Thelocation28

main(){staticcharbuffer[]="abcdefg";longpick;longoffset;charc; FILE*fp;fp=fopen("testdata","w");fwrite(buffer,1,7,fp); fclose(fp);fp=fopen("testdata","r");for(pick=3;pick<7;pick++){fseek(fp,pick,0);offset=ftell(fp);fscanf(fp,"%c",&c); printf("dataitematoffset%ldis%c\n",offset,c); }fclose(fp); }ThelocationofthefilepointerhapterSevenmain()Thelocationof29ThankYou!ThankYou!30ChapterSevenFileChapterSevenFile31Contents

Introduction1Open/closefile2Read/writefile

3

Checkthestateoftheopeningfile4Thelocationofthefilepointer54hapterSevenContentsIntroduction1Open/clo32Howtogetthedatawhilerunaprogram?Wherewilltheresultin?Howcaninputtheresultofaprogramtoanotherprogram?

Introduction

TheprocedureofClanguageEditLinkCreatetheprogramtextCompileCompileitsuccessfullyLinkittotheCfunctionlibrary

hapterSevenHowtogetthedatawhilerun33

Introductionprogram

formatoutputcharacteroutputstringoutputinitializationassignmentinputfromkeyboardmemorymemoryformatinputcharacterinputstringinputQuestionReaddatafromafileWritedatatoafilehapterSevenIntroductionprogramformato34

Introduction

Fileisthegatherofrelatedinformationsavedinmemorydevice(assistantmemory)

OSmanagessysteminfiles

Processingfilesmeansfileinput/outprocessing.Procedure1openfile2fileread/write3closefile.Interfaceinput/outdevicesaretreatedasfilesinC.Fileaccessingmethods:

1)BufferedI/O(orstreamI/O)2)UnbufferedI/O(orlow-levelI/O)hapterSevenIntroductionFileisth35

IntroductionBuffered(temporarystoragelocation)

We’lldiscussBufferedI/OinourlectureInbufferedI/O,---openacommunicationareainRAMDISkPROGRAMOutputfilebuffer

InputfilebufferTherearetwowaystodealwithfile:BinaryfileASCIIfilestreamhapterSevenIntroductionBuffered36

IntroductionstreamStreamistheabstractoffileusedtodealwithfile.TherearetwokindsofstreamsinC.ThecharacterisASCIIcode.oneASCIIcodeoccupiesonebyte,newline‘\n’isendofline.Afterread/writeacharacterfrom/toASCIIfile,thefpincreasesautomaticallytoguaranteetheread/writesequences.TextstreamBinarystreamStoringdatatodiskintheformthesameasinRAM.Example:10000Inbinaryfile,use2bytesInASCIIfile,use5byteshapterSevenIntroductionstreamStreamis37Open/closefileHowtomagangeafileinC?PointerOperationsopenfile（loadfile）operatefileusingfunctionsclosefile（removefilefrommemory）BDFACEAfilesystemcreatanewfiledeleteanoldoneread/write

accessafilebyitsnamemanagethememoryfileusedlimittheuser’srighthapterSevenOpen/closefileHowtomagange38Open/closefile

Filepointer,pointstoastructurethatcontainsinformationaboutthefile,suchasthelocationofabuffer,thecurrentcharacterpositioninthebuffer,whetherthefileisbeingreadorwritten,andwhethererrorsorendoffilehaveoccurred.Usersdon’tneedtoknowthedetails,becausethedefinitionsobtainedfrom<stdio.h>includeastructuredeclarationcalledFILE.

AboutfilepointerIamastudent.hapterSevenOpen/closefileFilepo39

2Thefunctionofopeningafile:FILE*fp;

uppercaseletters,otherwise,can’tberecognized,

definedtostandardstructure,key--word

#include<stdio.h>isnecessary

fopen(filename,*mode);stringchararraycharpointerpathsareallowed

1filespointer:openingafileusefunctionfopen()

readwriteappend……Open/closefilehapterSeven2Thefunctionofopeninga40Open/closefilefp=fopen(“file.txt”,“r”);openfile.txt,readinASCIIOpeningafilemeans….returnsafilepointerspecifytheoperationtobedone

definingafilenamefirst……pointstothefirstlocationoffilebuffer.r----readfile.txtwhichThereturnedvalueisassignedtoafilepointer.hapterSevenOpen/closefilefp=fopen(“fil41

Ifprocessissuccessful,thereturnedvalueisafilepointer.(address)FLIE*fp;Otherwise,returnNULLpointer.if((fp=fopen(“file.txt”“r”)==NULL)){printf(“can’topenfile\n”);exist(1);}Open/closefileSymbolExplanationrreadwwriteaappendtTextstreambBinarystream+Permitread/write

Iffopenfails,returnvalueiszero(NULLpointer)when:

1)fopenwantstoopenanonexistedfileforreading.2)readafilenotpermittedread.3)createafilebutdiskisfull.

4)disksectorisbad.hapterSevenIfprocessissuccessful,th423CloseafileCloseafileopened,argument&apointertofiletobeclosedinorderto1)releasefpand2)cleanupthebuffer.fclose(fp);Open/closefile

Openedfilemustbeclosedbeforeendingaprogram,otherwise,datamaybelost.hapterSeven3CloseafileCloseafileope43

Writesstringintofilepointedbystream

Fileread/writefgets(string,n,stream)

Readsastringofupton-1charactersfromstreamandplacesthemintostringfputs(string,stream)

1read/writefilefunctionsfgetc(fp),fputc(fp)

read/writeacharfrom/tofileread:c=fgetc(fp);readacharfromnamedfile.write:fputc(c,fp);writectonamedfile.Prototypeinstdio.hreturnEOF(-1)ifa)attheendoffile;b)detectinganerror;Usingfunctionfgets()andfputs()canrealizestringinput/ouputinfiles.hapterSevenWritesstringintofilepoi44

main(intargc,char*argv[]){intc;FILE*fpr,*fpd;if(argc!=3) {putchar('\007');puts("Usage:copyfile1,file2"); exit();} if((fpr=fopen(argv[1],"r"))==NULL) {printf("%c",'\007');printf("file%scan'topen\n",argv[1]); exit();} if((fpd=fopen(argv[2],"w"))==NULL) {printf("\files%scan'topen\n",argv[2]); exit();}while((c=fgetc(fpr))!=EOF)fputc(c,fpd);fclose(fpr);fclose(fpd);}Inputthreestrings(filename)Sourcefilenameobjectfilename

Thefunctionofthisprogramistocopyfile1tofile2hapterSevenmain(intargc,char45#include<stdio.h>main(){FILE*fp;charc1；fp=fopen(“file.dat”,”r”)；

c1=fgetc(fp);putchar(c1);fclose(fp);}#include<stdio.h>main(){FILE*fp;charch=‘a’;fp=fopen(“file.dat”,”w”);fputc(ch,fp);fclose(fp);}Readthecharacterfromfile.dat

writecharacter‘a’tofile.dat.

Fileread/writefscanf(stream,format,arg,...)

Readsdatafromstreamusingformatconversionspecifierintoaddressspecifierdbyarg.fprintf(stream,format,arg,...)

Writesargintostreamusingformatconversionspecifier.hapterSeven#include<stdio.h>#include<stdi46main(){FILE*fp;char*c1=“TurboC”;charc2[10];fp=fopen(“file2.dat”,”w”);

fputs(c1,fp);

fclose(fp);fp=fopen(“file2.dat”,”r”);

fgets(c2,8,fp);printf(“%s\n”,c2);fclose(fp);}

Fileread/write

readastringfromdeterminedfile(fp),haveread7chars;Returnedvalue:normalthe1stlocationofthestring;errororendoffileNULLwriteastringtodeterminedfile(fp)Returnedvalue:normal:thenumberofchars;error:NULLhapterSevenmain()Fileread/writeread47main(){FILE*fp;char*c1=“TurboC”;charc2[10];fp=fopen(“file3.dat”,”w”);fprintf(fp,”%s”,c1);fclose(fp);fp=fopen(“file3.dat”,”r”);fscanf(fp,”%s”,c2);printf(“%s\n”,c2);fclose(fp);}

Fileread/writeItissimilartoprintf,addfp–filepointerItissimilartoscanf,addfp–filepointerhapterSevenmain()Fileread/writeItiss48main(){FILE*fp;charstr[81],filename[80];gets(filename);if((fp=fopen(filename,”w”))==NULL){printf(“cannotopenthisfile\n”);exit(0);}while(strlen(gets(str))>0){fputs(str,fp);fputs(“\n”,fp);}fclose(fp);}Inputseveralstrings,thensavethemtodiskCanyouuse“filename”here?Howmanystringsshouldyouinput??

Fileread/writehapterSevenmain()Inputseveralstrings,49freadreadsnitemsofsizelengthfromstreamintobuffer.

Fileread/write

fwrite()/fread()*Twostandardlibraryfunctionsareavailabletofacilitatethestorageofdataarraysinbinaryforms.Thesearefwrite()andfread().fwrite(buffer,size,n,stream);fread(buffer,size,n,stream);

buffer:apointertothestartofthebuffertobewrittenintostream.

n:itemsinthebufferoflengthsizeinbytes.hapterSevenfreadreadsnitemsofsizele50

whencomputerarestarted,3standardfilesareopenedautomatically,and3associatedfilepointersareprovided。Userneedn'twritestatementstoopenstandardfilesandafterprogramareexecuted,standardfilesautomaticallyclosed.2Interfaceinput/outdevicesstdinfileinputstdoutstandardoutputpointerstderrerror

exit(1):returntoos.Innormalexistexit(0):---normalexist.3Exitfunctionsprogramwillstoprightaway.

Fileread/writehapterSevenwhencomputerares51Thefile’sstateisnecessarywhenusinginput/outfunctions,especiallytestingtheendofafile.Thereareonecoupleofwaystotesttheendoffile1EOF

Whenreading/writingASCIIfile,EOFisusedtotestifthefilepointerpointstotheendoffile,ifso,thevalueofEOFis-1Can’tsuitforbinaryfile2functionfeof()

feof(filepointername)

Thereturnvalueisnonzeroattheendoffile,Otherwise,itisnottheendoffile.CheckthestateoftheopeningfilehapterSevenThefile’sstateisnecessary52while(feof(fp)==0)c=fgetc(fp);Checkthestateoftheopeningfilewhile((c=fgetc(fp)!=EOF))

putchar(c);Example:readcharactersfromafilehapterSevenwhile(feof(fp)==0)Checkthe53Thelocationofhefilepointer1rewind

rewind(filepointername）

Setsfilepointertostreamtobeginningoffile2fseek

Locatesfilepointerforstreamatoffsetbytesfromorigins

fseek(filepointername，offsets，origin）

Noreturnvalue

GenerallyitisUsedforbinaryfile0:thebegining1:currentposition2:theend

Thenumberofbytes+movebackwards-moveforwards

return:azeroifthepointerwasreset