1. Chapter 7 Files By C. Shing ITEC Dept Radford University

2. Slide 2 Objectives 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 environment

3. Slide 3 File A stream of bytes Text file: user readable Binary file: machine readable, more efficient

4. Slide 4 File 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 specified

5. Slide 5 File 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);

6. Slide 6 Access 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 as FILE *filepointername; Example: FILE *infile, *outfile;

7. Slide 7 Access 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 fopen

8. Slide 8 Access 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 write

9. Slide 9 Access 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”);

10. Slide 10 Access 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 write

11. Slide 11 Access 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);

12. Slide 12 Access 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);

13. Slide 13 Access 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 outputfile Example: while (fgets(instring, n, infile) != EOF) fputs (instring, outfile);

14. Slide 14 Access 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 outputfile Example: int arrayA[n]; while (fread(arrayA, 4, n, infile) > 0) fwrite (arrayA, 4, n, outfile);

15. Slide 15 Access File by File Pointer – rewind Move pointer to the beginning of the file: Form: rewind (filepointer); Example: rewind (infile);

16. Slide 16 Access File by File Pointer – fseek Move pointer to any place of the file: fseek Form: fseek (filepointer, offset, position); Offset: relative to position -: to previous +: to next Position: 0: beginning 1: current position 2: end Example: fseek (outfile, 0, 2); // go to the end of the file

17. Slide 17 Access File by File Pointer – ftell check the current file position: ftell Form: ftell (filepointer); Example: while (ftell (infile)>0) putc(getc(infile), outfile);

18. Slide 18 Access File by File Pointer – feof check the end of file: feof Form: feof (filepointer); Example: while (!feof (infile)) putc(getc(infile), outfile);

19. Slide 19 Access File by File Pointer – fclose Form: fclose (filepointer); Example: fclose (infile); fclose (outfile);

20. Slide 20 Access File by File Pointer (Cont.) Class Example: Example1

21. Slide 21 Other Utilities Using File Pointer tmpfile(): returns a file pointer Example: FILE *tmpfileptr; tmpfileptr=tmpfile(); putc(getc(infile),tmpfileptr);

22. Slide 22 Access 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()

23. Slide 23 Access 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 descriptor

24. Slide 24 Access File by File Descriptor – open (Cont.) Example: #include int infilefd; infilefd=open(argv[1],O_CREAT, 0400);

25. Slide 25 Access File by File Descriptor – open (Cont.) Open file: (Cont.) Permission: defined in /usr/include/fcntl.h, use | to collect rights O_CREAT: create if not exists O_RDONLY: read only O_WRONLY: write only O_EXCL: give error if set O_CREAT and file exists O_RDWR: read and write

26. Slide 26 Access File by File Descriptor – open (Cont.) Open file: (Cont.) Permission: (Cont.) O_APPEND: file pointer at file end O_TRUNC: if file exists, truncate file to empty O_NONBLOCK: not block for named pipe

27. Slide 27 Access File by File Descriptor – open (Cont.) Open file: (Cont.) Example: infilefd=open (“/usr/include/stdio.h”, O_RDONLY); or outfilefd=open (argv[2], O_CREAT|O_WRONLY|O_TRUNC, 0600);

28. Slide 28 Access File by File Descriptor – read, write Read/Write file: for both text and binary files Input form: read (inputfd, bufferaddress, size) Read at most size bytes into buffer from inputfile, it returns numbers of bytes read Output form: write (outputfd, bufferaddress, size) Prints at most size bytes from buffer address into outputfile

29. Slide 29 Access File by File Descriptor – read, write (Cont.) Example: int size; char buffer[80]; while ((size=read(infilefd, buffer, 512)) > 0) write (outfilefd, buffer, size);

30. Slide 30 Access File by File Descriptor – lseek Move pointer to any place of the file: lseek Form: lseek (filefd, offset, position); Offset (long): relative to position -: to previous +: to next Position: defined in /usr/include/stdio.h or /usr/include/unistd.h 0 (or SEEK_SET): beginning 1 (or SEEK_CUR): current position 2 (or SEEK_END): end Example: lseek (outfilefd, 0, 2); // go to the end of the file

31. Slide 31 Access File by File Descriptor – close Form: close (filedescriptor); Example: close (infilefd); close (outfilefd);

32. Slide 32 Access File by File Descriptor (Cont.) Class Example: Example 2

33. Slide 33 Access File by File Descriptor (Cont.) Example: sparse.c sparse.txt normal.txt

34. Slide 34 Interacting with Operating Environment Call Unix command Use system tool Form: system (“Unix commands”); Wait program

35. Slide 35 Interacting with Operating Environment (Cont.) Send in output from Unix environment using pipe Open pipe Form: popen (“Unix command”, “permission”); Return a file pointer Close pipe Use pclose(filepointer)

36. Slide 36 Interacting with Operating Environment - system Example: system (“vi myfile”); Or char *cmdstr; sprintf(cmdstr, “vi %s”, argv[1]); system (cmdstr);

37. Slide 37 Interacting with Operating Environment – popen, pclose Example: FILE *fileptr; fileptr=popen (“find. -name myfile.c -print | more”, “r”); while ((character=getc(fileptr)) != EOF) putc(character, stdout); pclose(fileptr);

38. Slide 38 References Deitel & Deitel: C How to Program, 4th ed., Chapter 11, Prentice Hall