1. 27 April, 2000 CS1001 Lecture 25 Files Internal Files

2. 27 April, 2000 File Access OPEN the file READ from an existing file WRITE to a new file CLOSE the file

3. 27 April, 2000 OPEN Statement OPEN (open-list) where open-list is: Must include Unit Specifier Also includes: –FILE = Clause –STATUS = Clause –ACTION = Clause May include –POSITION = Clause – IOSTAT = Clause May include : –ERR = Clause –ACCESS = Clause –FORM = Clause –RECL = Clause –BLANK = Clause –PAD = Clause –DELIM = Clause

4. 27 April, 2000 Unit Specifier Required –May not be 0, 5, or 6 –0 is standard error output, mapped to unit 6 –5 is standard input, your keyboard –6 is standard output, your monitor –Has the form UNIT = integer-expression or simply integer-expression FILE = Clause FILE = character-expression, where character- expression is the filename e.g., FILE = “file.out”

5. 27 April, 2000 STATUS = Clause STATUS = character-expression, where character- expression can have one of the following values: –OLD meaning the file already exists –NEW meaning the file is being created –REPLACE creates a new file to replace an old file –SCRATCH no name for FILE= given, creates a work file that is deleted upon CLOSE –UNKNOWN default if STATUS= omitted e.g., STATUS = “NEW”

6. 27 April, 2000 IOSTAT = Clause IOSTAT = status-variable, where status-variable is an integer variable to which is assigned: –0 if the file is opened successfully –Positive value otherwise, representing the number of the error message in a list found in the system manuals e.g., IOSTAT = iOpenError then later on, check iOpenError

7. 27 April, 2000 ERR = Clause ERR = n, where n is the label of an executable statement that is the next statement executed if an error occurs in trying to open the file e.g., ERR = 30 30 PRINT *, “File Open Error = “, OpenError

8. 27 April, 2000 READ Statement READ (control-list) input-list –Must have a Unit Specifier –Must have a Format Specifier –Optional ADVANCE =Clause –Optional IOSTAT = Clause –Optional END = Clause –Optional ERR = Clause, same as OPEN –Optional REC = Clause for direct-access files e.g., READ (12, 10) iVariable, rVariable, cVariable 10 FORMAT (I4, F7.2, A12)

9. 27 April, 2000 END = Clause END = n, where n is the label of a statement to be executed when the end of a sequential file is encountered e.g., END = 40 40 PRINT *, “End of file reached”

10. 27 April, 2000 Comment on File Reading In a file like “student.dat” on page A17, to read in a last name, like “Peters”, you must read in: –All of the lines (records) up to that line –All of the line itself READ (12, 10) iStudNum, cLName, cName, cInit, & cAddress, iPhone, cGender, iClass, cMajor, iCredits, & iGPA 10 FORMAT (I5, A15, A15, A1, A22, I7, A1, I1, A4, I3, I3)

11. 27 April, 2000 WRITE Statement WRITE (control-list) output-list –Must have a Unit Specifier –Usually has a Format Specifier –Optional ERR = Clause –Optional IOSTAT = Clause –Optional REC = Clause e.g., WRITE (13, 10) iVar, rVar, cString 10 FORMAT (I4, F7.2, A12)

12. 27 April, 2000 ENDFILE Statement ENDFILE writes into the file a special record called and end-of-file record When encountered by a READ statement: –IOSTAT = clause condition can be detected –END = clause statement can be executed Once encountered, no more data can be transferred to or from this file unless the file is repositioned using REWIND or BACKSPACE

13. 27 April, 2000 CLOSE Statement CLOSE (close-list) where close-list is: –Must include Unit Specifier, same as OPEN –May include IOSTAT = Clause, same as OPEN –May include ERR = Clause, same as OPEN –May include STATUS = Clause –All files that are not closed by means of a CLOSE statement are automatically closed when an END or STOP statement is executed

14. 27 April, 2000 SUBROUTINE ReadList (Names, Numbers, Active, NumRecords) INTEGER, INTENT(IN) :: NumRecords CHARACTER *20, INTENT(OUT) :: Names(NumRecords) CHARACTER *13, INTENT(OUT) :: Numbers(NumRecords) LOGICAL, INTENT(OUT) :: Active(NumRecords) CHARACTER *20 :: Filename INTEGER :: i,Status PRINT *, 'Enter filename of input file: ' READ *, Filename OPEN (UNIT=1, ACCESS = 'sequential', FILE = Filename, & FORM = 'Formatted', STATUS = ’old') DO i = 1, NumRecords READ (1, 2, IOSTAT=Status) Names(i), Numbers(i), Active(i) 2 FORMAT (A20, A13,L1) IF (Status <= 0 ) EXIT END DO ENFILE(1) CLOSE (1) END SUBROUTINE ReadList

15. 27 April, 2000 Internal Files Sequence of memory locations containing information stored in character form and named by a character variable, array, or array element –Used to convert character information to numeric form –Used to convert character information into a character array Internal File Example Given cDate = “JULY 4, 1776” cYear = cDate(9:12) READ (UNIT = cYear, FMT = ‘(I4)’) iYear or READ (cYear, ‘(I4)’) iYear or READ (cDate(9:12), ‘(I4)’) iYear or READ (cDate, ‘(8X, I4)’) iYear Each of these takes the last four characters in the string cDate and converts it to an integer format named iYear

16. 27 April, 2000 OPEN Arguments Back up slides

17. 27 April, 2000 ACTION = Clause ACTION = i-o-action, where i-o-action is a character expression whose value is one of: –“READ” which opens the file for reading only –“WRITE” which opens the file for writing only –“READWRITE” which opens the file for reading and writing e.g., ACTION = “READ”

18. 27 April, 2000 POSITION = Clause POSITION = character-expression, where the value of character-expression is: –“REWIND” which positions the file at its initial point (beginning), default for new file –“APPEND” which positions the file at its end –“ASIS” leaves its position unchanged, default for an existing file already open e.g., POSITION = “REWIND”

19. 27 April, 2000 ACCESS = Clause ACCESS = access-method, where access-method can be either: –“SEQUENTIAL” meaning a file is accessed sequentially, without defined records –“DIRECT” for record oriented files, where each record has a record number for access e.g., ACCESS = ‘“SEQUENTIAL”

20. 27 April, 2000 FORM = Clause FORM = form-specifier, where form-specifier is a character expression that is either: –“FORMATTED” –‘UNFORMATTED” –If omitted, file is assumed formatted if sequential, unformatted if direct-access e.g., FORM = “FORMATTED”

21. 27 April, 2000 PAD = Clause Only applies to FORMATTED files PAD = character-expression, which can have the values: –“YES”, means the input proceeds as if the actual record were padded with blanks between fields –“NO” e.g., PAD =“YES” is the default

22. 27 April, 2000 RECL = Clause RECL = record-length, where record-length is an integer whose value must be positive –Only used for direct-access files and specifies the length of the records in the file –In a formatted file, the record length is the number of characters in a record e.g., RECL = 25

23. 27 April, 2000 BLANK = Clause Only applies to FORMATTED files BLANK = blank-specifier, which can be –“ZERO” –“NULL” The first causes blanks in numeric fields to be interpreted as zeros, the other causes blanks to be ignored. BLANK = “NULL” is default

24. 27 April, 2000 DELIM = Clause Only applies to FORMATTED files DELIM = character-expression, which can be: –“APOSTROPHE” is to be used as the delimiter for character strings written to a file –“QUOTE” is to be used as the delimiter for character strings written to a file –“NONE” –DELIM = “NONE” is the default

25. 27 April, 2000 STATUS = Clause STATUS = character-expression –“KEEP” may not be used for SCRATCH files. Otherwise the state of existence of the file remains unchanged (not deleted). –“DELETE” is the default if this clause is omitted, however, it depends upon a PERMANENCE property which can be “TEMPORARY” or “PERMANENT” –STATUS is usually not used

26. 27 April, 2000 READ Arguments Backup slides

27. 27 April, 2000 ADVANCE = Clause ADVANCE = character-expression, which can have the values: –“YES” specifies that output should advance to a new line after the current output has been completed –“NO” does not advance the output –ADVANCE = “YES” is the default

28. 27 April, 2000 IOSTAT = Clause IOSTAT = integer-variable, where –Positive value if an error occurs, usually the error number from a list in a manual –Negative value if the end of data occurs but no input error occurs –0 if neither an input error nor an end of data occurs

29. 27 April, 2000 REC = Clause REC = integer-expression, where integer- expression is positive and indicates the number of the record to be read from a direct-access file –Control list may not contain both an END = clause and a REC = clause e.g., REC = iPartNumber

30. 27 April, 2000 WRITE arguments Backup slides

31. 27 April, 2000 File-Positioning Statements REWIND unit or REWIND position-list BACKSPACE unit or BACKSPACE position-list ENDFILE unit or ENDFILE position-list Where position-list –Must contain unit or UNIT = unit –May contain ERR = clause –May contain IOSTAT = clause

32. 27 April, 2000 REWIND and BACKSPACE REWIND positions the file at the beginning of the file’s first record BACKSPACE positions the file at the beginning of the preceding record or line Neither has an affect if the file is already at the beginning e.g., REWIND 8 or REWIND (8, IOSTAT = iError)

33. 27 April, 2000 Not Needed For This Class INQUIRE Merging Files External Sorting Unformatted Files