课程资源linux程序设计ch3-1system programming

Ch3Ch3LinuxSystem–FileEnyiSoftwareInstituteofNanjingUniversityWhatisFileandFileAnobjectthatcanbewrittento,orreadfrom,orboth.Afilehascertainattributes,includingaccesspermissionsandtype.FileAcollectionoffilesandcertainoftheirattributes.Itprovidesanamespaceforfileserialnumbersreferringtothosefiles.文件系统的多种含FileTypesandFileregularcharacterspecialblockspecialsymbolicFileBytestream;noparticularinternalFileSystemsinVirtualFilesystemSwitchVFSVirtual;onlyexistsinsuperi-nodefiledentryExt2FileExt2HardlinkandsymbolicHard不 文件系Symbolic 文件系Review“lsSystemCalls&LibraryLinux内核的对外接口用户程序和内核之间唯一的接口;提供最小接口依赖于系统调用UnbufferedI/O&BufferedUnbufferedread/write->SystemFileNotinANSIC,butinPOSIX.1andBufferedImplementedinstandardI/O处理很多细节如缓存分配以优化长度执行I/O等Stream->apointertoBasicI/OSystemFileBasicopen/creat,close,read,write,FileFileAsmallnon-negativeint(inSTDIN_FILENO(0),STDOUT_FILENOSTDERR_FILENOGeneralstepsoffile/*arudimentaryexampleprogram{intfd,nread;charbuf[1024];/*openfile“data”forreading*/fd=open(“data”,O_RDONLY);/*readinthedatanread=read(fd,buf,/*closethefile}Openandpossiblycreateafileor#include<sys/types.h>#include<sys/stat.h>#include<fcntl.h>intopen(constchar*pathname,intintopen(constchar*pathname,intflags,mode_tmode);intcreat(constchar*pathname,mode_tmode);(Return:anewfiledescriptorifsuccess;-1ifParameter“flags”:fileaccessOneofO_RDONLY,O_WRONLYorO_RDWRwhichrequestopeningthefileread-only,write-onlyorread/write,respectively,bitwise-or‟dwithzeroormoreofthefollowing:(Alldefinedin O_APPEND:thefileisopenedinappendO_TRUNC:Ifthefilealreadyexistsandisaregularfileandtheopenmodeallowswritingwillbetruncatedtolength0.O_CREAT:IfthefiledoesnotexistitwillbeO_EXCL:WhenusedwithO_CREAT,ifthefilealreadyexistsitisanerrorandtheopenwillfail.…“creat”function:equivalenttoopenwithflagsequaltoO_CREAT|O_WRONLY|O_TRUNCParameter“mode”:specifiesthepermissionstouseincaseanewfileiscreated.Thevalueofparameter取 含S_IRGRPS_IXOTH

ReadbyownerWritebyownerExecutebyownerRead,writeandexecutebyReadbygroupWritebygroupRead,writeandexecutebygroupReadbyothersWritebyothersExecutebyothersRead,writeandexecutebyParameter“mode”&umask:afileprotectionTheinitialaccessmodeofanewmode&Closeafile#includeintclose(int(Return:0ifsuccess;-1ifReadfromafile#includessize_tread(intfd,void*buf,size_t(返回值读到的字节数，若已到文件尾为0，若出错为-Writetoafile#includessize_twrite(intfdconstvoid*bufsize_tcount);(返回值:若成功为已写的字节数，若出错为-1)while((n=read(STDIN_FILENO,buf,BUFSIZE))>if(write(STDOUT_FILENO,buf,n)!=err_sys(“writeiferr_sys(“readRepositionread/writefile#include#includeoff_tlseek(intfildes,off_toffset,int(Return:theresultingoffsetlocationifsuccess;-1ifThedirectiveSEEK_SET:theoffsetissetto“offset”SEEK_CUR:theoffsetissettoitscurrentlocation“offset”SEEK_END:theoffsetifsettothesizeofthefileplusDuplicateafile#includeintdup(intintdup2(intoldfd,int(Return:thenewfiledescriptorifsuccess;-1ifFileExample:Manipulateafile#include#includeintfcntl(intfd,intintfcntl(intfd,intcmd,longintfcntl(intfd,intcmd,structflock(返回值:若成功则依赖于cmd，若出错为-TheoperationisdeterminedbyfcntlFunctionThevalueofF_DUPFD:DuplicateafileexecF_GETOWN/F_SETOWN:ManageI/Oavailabilitydup/dup2andfcntlFunctionThevalueofF_DUPFD:DuplicateafileexecF_GETOWN/F_SETOWN:ManageI/Oavailabilitydup/dup2andControl#includeintioctl(intd,intrequest,StandardI/OFileStandardI/OFileStreamand“FILE”FILE*Predefinedpointer:stdin,stdout,BufferedThreetypesofFullLineNosetbuf/setvbufStreamBufferingThreetypesofblockbuffered(fullylinesetbuf,setvbuf#includevoidsetbuf(FILE*stream,charintsetvbuf(FILE*stream,char*buf,intmode,voidsetbuf(FILE ,charintsetvbuf(FILE*stream,char*buf,inttype,unsignedsize);StandardI/OStreamStream每次一个字符的每次一行的直接I/O(二进制格式化StreamStreamStreamOpena#includeFILE*fopen(constchar*filename,constcharintfclose(FILEParameter Opentextfilefor Truncatefiletozerolengthorcreatetextfile

OpenforOpenforreadingand Openforreadingandwriting.Thefileiscreatedifitdoesnotexist,otherwiseitistruncated. Openforreadingandappending.ThefileiscreateddoesnotStreamopen/closeCloseastream#include<stdio.h>intfclose(FILE*fp);(Return:0ifsuccess;-1ifInputofagetc,fgetc,getchar#include<stdio.h>intgetc(FILE*fp);intfgetc(FILE*fp);intgetchar(void);(Result:Readsthenextcharacterfromastreamreturnsitasanunsignedcharcasttoanint,EOFonendoffileorThreeferror,feof,ungetcfunction:pushacharacterbacktoaOutputofaputc,fputc,putchar#includeintputc(intc,FILE*fp);intfputc(intc,FILE*fp);intputchar(intc);(Return:thecharacterifsuccess;-1ifInputofaLineoffgets,gets#includechar*fgets(char*s,intsize,FILEchar*gets(char fgets:readsinatmostsize-1charactersfromstreamandstoresthemintothebufferpointedbys.ReadingstopsafteranEOForanewline.A„\0‟characterisstoredattheendofthebuffer.OutputofaLineoffputs,puts#includeintfputs(constchar*s,FILEintputs(constcharQuestion:I/ORewritegetc/putcBinaryStreamfread/fwrite#includesize_tfread(void*ptr,size_tsize,size_tnmemb,FILEsizefwrite(constvoid*ptr,size_tsize,size_tnmemb,FILE(Return:thenumberofaitemssuccessfullyreadorBinarystreamRead/writeabinaryfloatif(fwrite(&data[2],sizeof(float),4,fp)!=4err_sys(“fwriteRead/writeastructshort long charif(fwrite(&item,sizeof(item),1,fp)!=err_sys(“fwriteFormattedscanf,fscanf,sscanf#includeintscanf(constchar*format,intfscanf(FILE*stream,constchar*format,intsscanf(constchar*str,constchar*format,Usefgets,thenparsetheFormattedI/Oprintf,fprintf,sprintf#includeintprintf(constchar*format,intfprintf(FILE*stream,constchar*format,intsprintf(char*str,constchar*format,Repositionafseek, l,rewind#includeintfseek(FILE*stream,longintoffset,intlong l(FILEvoidrewind(FILEfgetpos,fsetposfunctions(IntroducedinANSI#includeintfgetpos(FILE*fp,fpos_tintfsetpos(FILE*fp,constfpos_tFlusha#includeintfflush(FILEStreamandFile#include<stdio.h>intfileno(FILE#includeFILE*fdopen(intfildes,constcharTemporaryCreateanameforatemporary#includechar*tmpnam(char(返回值:指向唯一路径名的指针Createatemporary#include<stdio.h>FILE*tmpfile(void);(返回值:若成功为文件指针，若出错为AdvancedSystemHandlingfileHandlingGetfilestatus#include<sys/stat.h>#include<unistd.h>intstat(constchar*filename,structstatintfstat(intfiledes,structstatintlstat(constchar*file_name,structstat(Return:0ifsuccess;-1ifstructstructstatmode_tst_mode;/*filetype&

/*inodenumber(serialnumber)*/ /*devicenumber(filesystem)*/st_nlink;/*linkcount*/ /*userIDof /*groupIDofowner*/ /*sizeoffile,inbytes*/st_atime;/*timeoflastaccess*/st_mtime;/*timeoflastmodification*/st_ctime;/*timeoflastfilestatus

/*Optimalblocksizefor/*number512-byteblocksTestmacrosforfileDefinedin File

regularcharacterspecialblockspecialsymbolicFilePermission-DeepintoSUID,SGID,StickyFile

含ReadbyownerWritebyownerExecutebyownerRead,writeandexecutebyReadbygroupWritebygroupRead,writeandexecutebyReadbyothersWritebyothersExecutebyothersRead,writeandexecutebyFilepermission

含SetuserIDonexecutionSetgroupIDonexecutionSaved-textbit(stickybit)Example:testingfileif(buf.st_mode&printf(“readablebyprintf(“unreadablebyaccess#includeintaccess(constchar*pathname,intmode);(Return:0ifsuccess;-1iffailure)ParameterR_OK,W_OK,X_OK, odChangepermissionsofa od(constchar*path,mode_tmode);intf od(intfildes,mode_tmode);(Return:0ifsuccess;-1iffailure)Changeownershipofafile#include<sys/types.h>#include<unistd.h>intchown(constchar*path,uid_towner,gid_tgroup);intfchown(intfd,uid_towner,gid_tgroup);intlchown(constchar*path,uid_towner,gid_t(Return:0ifsuccess;-1ifumask为进程设置文件存取权 #include<sys/stat.h>mode_tumask(mode_tCreateanewlinkto(makeanewnamefor)a#includeintlink(constchar*oldpath,constchar (Return:0ifsuccess;-1ifDeleteanameandpossiblythefileitrefers#includeintunlink(constchar*pathname);(Return:0ifsuccess;-1ifCreateasymboliclink(named thcontainsthesting#includeintsymlink(constchar*oldpath,constchar (Return:0ifsuccess;-1ifReadvalueofasymbolic#includeintreadlink(constchar*path,char*buf,size_t(Return:thecountof cedinthebufferif-1ifHandlingchdir/fchdir,Readamkdir/rmdir#include#includeintmkdir(constchar*pathname,mode_t(Return:0ifsuccess;-1if#includeintrmdir(constchar(Return:0ifsuccess;-1ifChangeworking#includeintchdir(constcharintfchdir(int(Return:0ifsuccess;-1if cd(1)getcwd获得当前工 的绝对路#includechar*getcwd(char*buf,size_t(返回值:若成功则为buf，若出错则为ReadaDataDIR,structDat