Chapter 7 FilesObjectivesFileFile AccessFile UtilitiesAccess File by File PointerAccess File by File Pointer - fopenAccess File by File Pointer – fopen (Cont.)Slide 9Slide 10Access File by File Pointer – fscanf, fprintfAccess File by File Pointer – getc, putcAccess File by File Pointer – fgets, fputsAccess File by File Pointer – fread, fwriteAccess File by File Pointer – rewindAccess File by File Pointer – fseekAccess File by File Pointer – ftellAccess File by File Pointer – feofAccess File by File Pointer – fcloseAccess File by File Pointer (Cont.)Other Utilities Using File PointerAccess File by File DescriptorAccess File by File Descriptor - openAccess File by File Descriptor – open (Cont.)Slide 25Slide 26Slide 27Access File by File Descriptor – read, writeAccess File by File Descriptor – read, write (Cont.)Access File by File Descriptor – lseekAccess File by File Descriptor – closeAccess File by File Descriptor (Cont.)Slide 33Interacting with Operating EnvironmentInteracting with Operating Environment (Cont.)Interacting with Operating Environment - systemInteracting with Operating Environment – popen, pcloseReferencesChapter 7 FilesBy C. ShingITEC DeptRadford UniversitySlide 2ObjectivesUnderstand how to use file utilitiesUnderstand how to use files by file pointersUnderstand how to use files by file descriptorsUnderstand how to interact with operating environmentSlide 3FileA stream of bytesText file: user readableBinary file: machine readable, more efficientSlide 4File AccessCan access (by opening file first) byFile pointer: address of a structure FILE * defined in stdio.hHas buffer availableFile descriptor: non-negative number represents fileNo data structure, flexibleNeeds to define buffer to hold more than 1 characterNo formatting specifiedSlide 5File UtilitiesCreate a temporary filetmpnam (NULL)Returns a string of a temporary file nameDelete fileremove (filenamestring);Change filenamerename (oldname string, newnamestring);Example: char *tmpfile;tmpfile=tmpnam(NULL);remove (tmpfile);Slide 6Access File by File PointerFile pointer: declare for each file usedPre-defined: stdin (keyboard input), stdout (output to screen),stderr (error message to screen)Declared asFILE *filepointername;Example:FILE *infile, *outfile;Slide 7Access File by File Pointer - fopenOpen file:Form: fopen (“filename”, ”permission”)Returns a file pointer Starts from beginning of the fileNeed to check successful when use fopenSlide 8Access File by File Pointer – fopen (Cont.)Open file: (Cont.)Permission:Unix: both text and binary filer: read, for inputw: write, for outputIf file not exist, create itIf file exists, erase file content a: append to end of file, for updatingIf file not exist, create itr+. w+: read and writeSlide 9Access File by File Pointer – fopen (Cont.)Open file: (Cont.)Example:infile=fopen (“/usr/include/stdio.h”, “r”); or outfile=fopen (“current_dir_file”, “w”); or outfile=fopen (argv[1], “a”);Slide 10Access File by File Pointer – fopen (Cont.)Open file: (Cont.)Permission: (Cont.)MS-DOSTex file: same as in UnixBinary file:rb: readwb: writeab: appendr+, w+: read and writeSlide 11Access File by File Pointer – fscanf, fprintfRead/Write file: for text fileAny data typeInput form:fscanf(inputfilepointer, “format”, variable_addr)Output form:fprintf(outputfilepointer, “format”, variable_list)Example:char character;while (fscanf(infile,”%c”,&character) != EOF)fprintf (outfile, ”%c”, character);Slide 12Access File by File Pointer – getc, putcRead/Write file:CharacterInput form: getc (inputfilepointer)Output form: putc (character_variable, outputfilepointer)Example:char character;while ((character=getc(infile)) != EOF)putc (character, outfile);Slide 13Access File by File Pointer – fgets, fputsRead/Write file:StringInput form: fgets (string, n, inputfilepointer)Read at most n-1 characters into string from inputfileOutput form: fputs (string, outputfilepointer)Writes the string (except NULL character into outputfileExample:while (fgets(instring, n, infile) != EOF)fputs (instring, outfile);Slide 14Access File by File Pointer – fread, fwriteRead/Write file: for binary fileInput form: fread (arrayaddress, cellsize, n, inputfilepointer)Read at most n*cellsize bytes into arrayaddress from inputfileOutput form: fwrite (arrayaddress, cellsize, n, outputfilepointer)Writes at most n*cellsize bytes from arrayaddress into outputfileExample:int arrayA[n];while (fread(arrayA, 4, n, infile) > 0)fwrite (arrayA, 4, n, outfile);Slide 15Access File by File Pointer – rewindMove pointer to the beginning of the file:Form: rewind (filepointer);Example:rewind (infile);Slide 16Access File by File Pointer – fseekMove pointer to any place of the file: fseekForm: fseek (filepointer, offset, position);(Byte) Offset (int): relative to position-: to previous+: to nextPosition:0: beginning1: current position2: endExample:fseek (outfile, 0, 2); // go to the end of the fileSlide 17Access File by File Pointer – ftellcheck the current file position: ftellForm: ftell (filepointer);Example:while (ftell (infile)>0) putc(getc(infile), outfile);Slide 18Access File by File Pointer – feofcheck the end of file: feofForm: feof (filepointer);Example:while (!feof (infile)) putc(getc(infile), outfile);Slide 19Access File by File Pointer – fcloseForm: fclose (filepointer);Example:fclose (infile);fclose (outfile);Slide 20Access File by File Pointer (Cont.)Class Example: Example1(Bubble) Sort Structure using Files:Program, Data, OutputSlide 21Other Utilities Using File Pointertmpfile(): returns a file pointerExample:FILE *tmpfileptr; tmpfileptr=tmpfile();putc(getc(infile),tmpfileptr);Slide 22Access File by File DescriptorFile descriptor: nonnegative integer for each file Reserved: 0 (stdin), 1 (stdout), 2 (stderr)The rest files starts using 3, created when use open()Slide 23Access File by File Descriptor - openOpen file:Starts from beginning of the fileDefined in unistd.h (in MS-DOS, use io.h)check successful when use openForm: open (“filename”, options, permission_octal)Returns a file descriptorSlide 24Access File by File Descriptor – open