HP OpenVMS Systems Documentation

HP OpenVMS Programming Concepts Manual

Example 28-2 shows the code for performing the same functions as Example 28-1 but in an Alpha system's environment.

Example 28-2 Mapping a Data File to the Common Block on an Alpha System

!INCOME.OPT

PSECT_ATTR = INC_DATA, SOLITARY, SHR, WRT

INCOME.FOR

! Declare variables to hold statistics
REAL PERSONS_HOUSE (2048),
2    ADULTS_HOUSE (2048),
2    INCOME_HOUSE (2048)
INTEGER TOTAL_HOUSES, STATUS
! Declare section information
! Data area
COMMON /INC_DATA/ PERSONS_HOUSE,
2                 ADULTS_HOUSE,
2                 INCOME_HOUSE,
2                 TOTAL_HOUSES
! Addresses
INTEGER ADDR(2),
2       RET_ADDR(2)
! Section length
INTEGER SEC_LEN
! Channel
INTEGER*2 CHAN,
2         GARBAGE
COMMON /CHANNEL/ CHAN,
2                GARBAGE
! Mask values
INTEGER MASK
INCLUDE '($SECDEF)'
! User-open routines
INTEGER UFO_OPEN,
2       UFO_CREATE
EXTERNAL UFO_OPEN,
2        UFO_CREATE
! Declare logical unit number
INTEGER STATS_LUN
! Declare status variables and values
INTEGER STATUS,
2       IOSTAT,
2       IO_OK
PARAMETER (IO_OK = 0)
INCLUDE '($FORDEF)'
EXTERNAL INCOME_BADMAP
! Declare logical for INQUIRE statement
LOGICAL EXIST
! Declare subprograms invoked as functions
INTEGER LIB$GET_LUN,
2       SYS$CRMPSC,
2       SYS$DELTVA,
2       SYS$DASSGN
! Get logical unit number for STATS.SAV
STATUS = LIB$GET_LUN (STATS_LUN)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
INQUIRE (FILE = 'STATS.SAV',
2        EXIST = EXIST)
IF (EXIST) THEN
  OPEN (UNIT=STATS_LUN,
2       FILE='STATS.SAV',
2       STATUS='OLD',
2       USEROPEN = UFO_OPEN)
  MASK = SEC$M_WRT
ELSE
  ! If STATS.SAV does not exist, create new database
  MASK = SEC$M_WRT .OR. SEC$M_DZRO
  SEC_LEN =
!  (address of last - address of first + size of last + 511)/512
2  ( (%LOC(TOTAL_HOUSES) - %LOC(PERSONS_HOUSE(1)) + 4 + 511)/512 )
  OPEN (UNIT=STATS_LUN,
2       FILE='STATS.SAV',
2       STATUS='NEW',
2       INITIALSIZE = SEC_LEN,
2       USEROPEN = UFO_CREATE)
END IF
! Free logical unit number and map section
CLOSE (STATS_LUN)
! ********
! MAP DATA
! ********
STATUS = LIB$GETSYI(SYI$_PAGE_SIZE, PAGE_MAX,,,,)
IF (.NOT. STATUS) CALL LIB$STOP (%VAL (STATUS))
! Specify first and last address of section
ADDR(1) = %LOC(PERSONS_HOUSE(1))
! Section will always be smaller than page_max bytes
ADDR(2) = ADDR(1) + PAGE_MAX -1
! Map the section
STATUS = SYS$CRMPSC (ADDR,
2                    RET_ADDR,
2                    ,
2                    %VAL(MASK),
2                    ,,,
2                    %VAL(CHAN),
2                    ,,,)
IF (.NOT. STATUS) CALL LIB$SIGNAL(%VAL(STATUS))
! Check for correct mapping
IF (ADDR(1) .NE. RET_ADDR (1))

2  CALL LIB$SIGNAL (%VAL (%LOC(INCOME_BADMAP)))
   .
   .
   .
                     ! Reference data using the
                     ! data structures listed
                     ! in the common block
   .
   .
   .
! Close and update STATS.SAV
STATUS = SYS$DELTVA (RET_ADDR,,)
IF (.NOT. STATUS) CALL LIB$SIGNAL(%VAL(STATUS))
STATUS = SYS$DASSGN (%VAL(CHAN))
IF (.NOT. STATUS) CALL LIB$SIGNAL(%VAL(STATUS))

END

28.4.1.2 Using the User-Open Routine

When you open a file for mapping in Fortran, for example, you must specify a user-open routine ( Section 28.6 discusses user-open routines) to perform the following operations:

Set the user-file open bit (FAB$V_UFO) in the file access block (FAB) options mask.
Open the file using SYS$OPEN for an existing file or SYS$CREATE for a new file. (Do not invoke SYS$CONNECT if you have set the user-file open bit.)
Return the channel number to the program unit that started the OPEN operation. The channel number is in the additional status longword of the FAB (FAB$L_STV) and must be returned in a common block.
Return the status of the open operation (SYS$OPEN or SYS$CREATE) as the value of the user-open routine.

After setting the user-file open bit in the FAB options mask, you cannot use language I/O statements to access data in that file. Therefore, you should free the logical unit number associated with the file. The file is still open. You access the file with the channel number.

Example 28-3 shows a user-open routine invoked by the sample program in Section 28.4.1.1 if the file STATS.SAV exists. (If STATS.SAV does not exist, the user-open routine must invoke SYS$CREATE rather than SYS$OPEN.)

Example 28-3 Using a User-Open Routine

!UFO_OPEN.FOR

INTEGER FUNCTION UFO_OPEN (FAB,
2                          RAB,
2                          LUN)

! Include Open VMS RMS definitions
INCLUDE '($FABDEF)'
INCLUDE '($RABDEF)'
! Declare dummy arguments
RECORD /FABDEF/ FAB
RECORD /RABDEF/ RAB
INTEGER LUN
! Declare channel
INTEGER*4 CHAN
COMMON /CHANNEL/ CHAN
! Declare status variable
INTEGER STATUS
! Declare system procedures
INTEGER SYS$OPEN
! Set useropen bit in the FAB options longword
FAB.FAB$L_FOP = FAB.FAB$L_FOP .OR. FAB$M_UFO
! Open file
STATUS = SYS$OPEN (FAB)
! Read channel from FAB status word
CHAN = FAB.FAB$L_STV

! Return status of open operation
UFO_OPEN = STATUS

END

28.4.1.3 Initializing a Mapped Database

The first time you map a file you must perform the following operations in addition to those listed at the beginning of Section 28.4.1:

Specify the size of the file---SYS$CRMPSC maps data based on the size of the file. Therefore, when creating a file that is to be mapped, you must specify in your program a file large enough to contain all of the expected data. Figure the size of your database as follows:
- Find the size of the common block (in bytes)---Subtract the location of the first variable in the common block from the location of the last variable in the common block and then add the size of the last element.
- Find the number of blocks in the common block---Add 511 to the size and divide the result by 512 (512 bytes = 1 block).
Initialize the file when you map it---The blocks allocated to a file might not be initialized and therefore contain random data. When you first map the file, you should initialize the mapped area to zeros by setting the SEC$V_DZRO bit in the mask argument of SYS$CRMPSC.

The user-open routine for creating a file is the same as the user-open routine for opening a file except that SYS$OPEN is replaced by SYS$CREATE.

28.4.1.4 Saving a Mapped File

To close a data file that was opened for user I/O, you must deassign the I/O channel assigned to that file. Before you can deassign a channel assigned to a mapped file, you must delete the virtual memory associated with the file (the memory used by the common block). When you delete the virtual memory used by a mapped file, any changes made while the file was mapped are written back to the disk file. Use the Delete Virtual Address Space (SYS$DELTVA) system service to delete the virtual memory used by a mapped file. Use the Deassign I/O Channel (SYS$DASSGN) system service to deassign the I/O channel assigned to a file.

The program segment shown in Example 28-4 closes a mapped file, automatically writing any modifications back to the disk. To ensure that the proper locations are deleted, pass SYS$DELTVA the addresses returned to your program by SYS$CRMPSC rather than the addresses you passed to SYS$CRMPSC. If you want to save modifications made to the mapped section without closing the file, use the Update Section File on Disk (SYS$UPDSEC) system service. To ensure that the proper locations are updated, pass SYS$UPDSEC the addresses returned to your program by SYS$CRMPSC rather than the addresses you passed to SYS$CRMPSC. Typically, you want to wait until the update operation completes before continuing program execution. Therefore, use the efn argument of SYS$UPDSEC to specify an event flag to be set when the update is complete, and wait for the system service to complete before continuing. For a complete description of the SYS$DELTVA, SYS$DASSGN, and SYS$UPDSEC system services, see the HP OpenVMS System Services Reference Manual.

Example 28-4 Closing a Mapped File

! Section address
INTEGER*4 ADDR(2),
2         RET_ADDR(2)
! Event flag
INTEGER*4 FLAG
! Status block
STRUCTURE /IO_BLOCK/
  INTEGER*2 IOSTAT,
2           HARDWARE
  INTEGER*4 BAD_PAGE
END STRUCTURE
RECORD /IO_BLOCK/ IOSTATUS
   .
   .
   .
! Get an event flag
STATUS = LIB$GET_EF (FLAG)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL(STATUS))
! Update the section
STATUS = SYS$UPDSEC (RET_ADDR,
2                    ,,,
2                    %VAL(FLAG)
2                    ,
2                    IOSTATUS,,)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL(STATUS))
! Wait for section to be updated
STATUS = SYS$SYNCH (%VAL(FLAG),
2                   IOSTATUS)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL(STATUS))
   .
   .
   .

28.5 Opening and Updating a Sequential File

This section provides an example, written in HP Fortran, of how to open and update a sequential file on a VAX system. A sequential file consists of records arranged one after the other in the order in which they are written to the file. Records can only be added to the end of the file. Typically, sequential files are accessed sequentially.

Creating a Sequential File

To create a sequential file, use the OPEN statement and specify the following keywords and keyword values:

STATUS ='NEW'
ACCESS = 'SEQUENTIAL'
ORGANIZATION = 'SEQUENTIAL'

The file structure keyword ORGANIZATION also accepts the value 'INDEXED' or 'RELATIVE'.

Example 28-5 creates a sequential file of fixed-length records.

Example 28-5 Creating a Sequential File of Fixed-Length Records

   .
   .
   .
INTEGER STATUS,
2       LUN,
2       LIB$GET_INPUT,
2       LIB$GET_LUN,
2       STR$UPCASE
INTEGER*2     FN_SIZE,
2             REC_SIZE
CHARACTER*256 FILENAME
CHARACTER*80  RECORD
! Get file name
STATUS = LIB$GET_INPUT (FILENAME,
2                       'File name: ',
2                       FN_SIZE)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
! Get free unit number
STATUS = LIB$GET_LUN (LUN)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
! Open the file
OPEN (UNIT = LUN,
2     FILE = FILENAME (1:FN_SIZE),
2     ORGANIZATION = 'SEQUENTIAL',
2     ACCESS = 'SEQUENTIAL',
2     RECORDTYPE = 'FIXED',
2     FORM = 'UNFORMATTED',
2     RECL = 20,
2     STATUS = 'NEW')
! Get the record input
STATUS = LIB$GET_INPUT (RECORD,
2                       'Input: ',
2                       REC_SIZE)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
DO WHILE (REC_SIZE .NE. 0)

  ! Convert to uppercase
  STATUS = STR$UPCASE (RECORD,RECORD)
  IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))

  WRITE  (UNIT=LUN) RECORD(1:REC_SIZE)
  ! Get more record input
  STATUS = LIB$GET_INPUT (RECORD,
2                         'Input: ',
2                         REC_SIZE)
  IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))

END DO

END

Updating a Sequential File

To update a sequential file, read each record from the file, update it, and write it to a new sequential file. Updated records cannot be written back as replacement records for the same sequential file from which they were read.

Example 28-6 updates a sequential file, giving the user the option of modifying a record before writing it to the new file. The same file name is used for both files; because the new update file was opened after the old file, the new file has a higher version number.

Example 28-6 Updating a Sequential File

   .
   .
   .
INTEGER STATUS,
2       LUN1,
2       LUN2,
2       IOSTAT
INTEGER*2  FN_SIZE
CHARACTER*256 FILENAME
CHARACTER*80 RECORD
CHARACTER*80 NEW_RECORD
INCLUDE '($FORDEF)'
INTEGER*4 LIB$GET_INPUT,
2         LIB$GET_LUN,
2         STR$UPCASE
! Get file name
STATUS = LIB$GET_INPUT (FILENAME,
2                       'File name: ',
2                       FN_SIZE)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
! Get free unit number
STATUS = LIB$GET_LUN (LUN1)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
! Open the old file
OPEN (UNIT=LUN1,
2     FILE=FILENAME (1:FN_SIZE),
2     ORGANIZATION='SEQUENTIAL',
2     ACCESS='SEQUENTIAL',
2     RECORDTYPE='FIXED',
2     FORM='UNFORMATTED',
2     RECL=20,
2     STATUS='OLD')
! Get free unit number
STATUS = LIB$GET_LUN (LUN2)
IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
! Open the new file
OPEN (UNIT=LUN2,
2     FILE=FILENAME (1:FN_SIZE),
2     ORGANIZATION='SEQUENTIAL',
2     ACCESS='SEQUENTIAL',
2     RECORDTYPE='FIXED',
2     FORM='UNFORMATTED',
2     RECL=20,
2     STATUS='NEW')
! Read a record from the old file
READ (UNIT=LUN1,
2     IOSTAT=IOSTAT) RECORD
IF (IOSTAT .NE. IOSTAT_OK) THEN
  CALL ERRSNS (,,,,STATUS)
  IF (STATUS .NE. FOR$_ENDDURREA) THEN
    CALL LIB$SIGNAL (%VAL(STATUS))
  END IF
END IF

DO WHILE (STATUS .NE. FOR$_ENDDURREA)

  TYPE *, RECORD

  ! Get record update
  STATUS = LIB$GET_INPUT (NEW_RECORD,
2                         'Update: ')
  IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))
  ! Convert to uppercase
  STATUS = STR$UPCASE (NEW_RECORD,
2                      NEW_RECORD)
  IF (.NOT. STATUS) CALL LIB$SIGNAL (%VAL (STATUS))

  ! Write unchanged record or updated record
  IF (NEW_RECORD .EQ. ' ' ) THEN
    WRITE (UNIT=LUN2) RECORD
  ELSE
    WRITE (UNIT=LUN2) NEW_RECORD
  END IF

  ! Read the next record
  READ (UNIT=LUN1,
2       IOSTAT=IOSTAT) RECORD
  IF (IOSTAT .NE. IOSTAT_OK) THEN
    CALL ERRSNS (,,,,STATUS)
    IF (STATUS .NE. FOR$_ENDDURREA) THEN
      CALL LIB$SIGNAL (%VAL(STATUS))
    END IF
  END IF
END DO

END

28.6 User-Open Routines

A user-open routine in Fortran, for example, gives you direct access to the file access block (FAB) and record access block (RAB) (the OpenVMS RMS structures that define file characteristics). Use a user-open routine to specify file characteristics that are otherwise unavailable from your programming language.

When you specify a user-open routine, you open the file rather than allow the program to open the file for you. Before passing the FAB and RAB to your user-open routine, any default file characteristics and characteristics that can be specified by keywords in the programming language are set. Your user-open routine should not set or modify such file characteristics because the language might not be aware that you have set the characteristics and might not perform as expected.

28.6.1 Opening a File

Section 28.4.1.2 provides guidelines on opening a file with a user-open routine. This section provides an example of a Fortran user-open routine.

28.6.1.1 Specifying USEROPEN

To open a file with a user-open routine, include the USEROPEN specifier in the Fortran OPEN statement. The value of the USEROPEN specifier is the name of the routine (not a character string containing the name). Declare the user-open routine as an INTEGER*4 function. Because the user-open routine name is specified as an argument, it must be declared in an EXTERNAL statement.

The following statement instructs Fortran to open SECTION.DAT using the routine UFO_OPEN:

! Logical unit number
INTEGER LUN

! Declare user-open routine
INTEGER UFO_OPEN
EXTERNAL UFO_OPEN
   .
   .
   .
OPEN (UNIT = LUN,
2     FILE = 'SECTION.DAT',
2     STATUS = 'OLD',
2     USEROPEN = UFO_OPEN)
   .
   .
   .

Note that Fortran can use the $RAB64DEF style of RABs. Code that uses USEROPEN should expected this types of structure. RTL internally uses NAM$C_MAXRSS as a length limit, and file names must reside in a low memory address.

28.6.1.2 Writing the User-Open Routine

Write a user-open routine as an INTEGER function that accepts three dummy arguments:

FAB address---Declare this argument as a RECORD variable. Use the record structure FABDEF defined in the $FABDEF module of SYS$LIBRARY:FORSYSDEF.TLB.
RAB address---Declare this argument as a RECORD variable. Use the record structure RABDEF defined in the $RABDEF module of SYS$LIBRARY:FORSYSDEF.TLB.
Logical unit number---Declare this argument as an INTEGER.

A user-open routine must perform at least the following operations. In addition, before opening the file, a user-open routine usually adjusts one or more fields in the FAB or the RAB or in both.

Opens the file---To open the file, invoke the SYS$OPEN system service if the file already exists, or the SYS$CREATE system service if the file is being created.
Connects the file---Invoke the SYS$CONNECT system service to establish a record stream for I/O.
Returns the status---To return the status, equate the return status of the SYS$OPEN or SYS$CREATE system service to the function value of the user-open routine.

The following user-open routine opens an existing file. The file to be opened is specified in the OPEN statement of the invoking program unit.

UFO_OPEN.FOR

INTEGER FUNCTION UFO_OPEN (FAB,
2                          RAB,
2                          LUN)

! Include Open VMS RMS definitions
INCLUDE '($FABDEF)'
INCLUDE '($RABDEF)'
! Declare dummy arguments
RECORD /FABDEF/ FAB
RECORD /RABDEF/ RAB
INTEGER LUN
! Declare status variable
INTEGER STATUS
! Declare system routines
INTEGER SYS$CREATE,
2       SYS$OPEN,
2       SYS$CONNECT
! Optional FAB and/or RAB modifications
   .
   .
   .
! Open file
STATUS = SYS$OPEN (FAB)
IF (STATUS)
2  STATUS = SYS$CONNECT (RAB)

! Return status of $OPEN or $CONNECT
UFO_OPEN = STATUS

END

28.6.1.3 Setting FAB and RAB Fields

Each field in the FAB and RAB is identified by a symbolic name, such as FAB$L_FOP. Where separate bits in a field represent different attributes, each bit offset is identified by a similar symbolic name, such as FAB$V_CTG. The first three letters identify the structure containing the field. The letter following the dollar sign indicates either the length of the field (B for byte, W for word, or L for longword) or that the name is a bit offset (V for bit) rather than a field. The letters following the underscore identify the attribute associated with the field or bit. The symbol FAB$L_FOP identifies the FAB options field, which is a longword in length; the symbol FAB$V_CTG identifies the contiguity bit within the options field.

The STRUCTURE definitions for the FAB and RAB are in the $FABDEF and $RABDEF modules of the library SYS$LIBRARY:FORSYSDEF.TLB. To use these definitions, do the following:

Include the modules in your program unit.
Declare RECORD variables for the FAB and the RAB.
Reference the various fields of the FAB and RAB using the symbolic name of the field.

The following user-open routine specifies that the blocks allocated for the file must be contiguous. To specify contiguity, you clear the best-try-contiguous bit (FAB$V_CBT) of the FAB$L_FOP field and set the contiguous bit (FAB$V_CTG) of the same field.

UFO_CONTIG.FOR

INTEGER FUNCTION UFO_CONTIG (FAB,
2                            RAB,
2                            LUN)

! Include Open VMS RMS definitions
INCLUDE '($FABDEF)'
INCLUDE '($RABDEF)'
! Declare dummy arguments
RECORD /FABDEF/ FAB
RECORD /RABDEF/ RAB
INTEGER LUN
! Declare status variable
INTEGER STATUS
! Declare system procedures
INTEGER SYS$CREATE,
2       SYS$CONNECT
! Clear contiguous-best-try bit and
! set contiguous bit in FAB options
FAB.FAB$L_FOP = IBCLR (FAB.FAB$L_FOP, FAB$V_CBT)
FAB.FAB$L_FOP = IBSET (FAB.FAB$L_FOP, FAB$V_CTG)
! Open file
STATUS = SYS$CREATE (FAB)
IF (STATUS) STATUS = SYS$CONNECT (RAB)

! Return status of open or connect
UFO_CONTIG = STATUS

END

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