Document revision date: 15 July 2002
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OpenVMS Programming Concepts Manual
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28.3.2 Shared Access

The Fortran specifier READONLY and the SHARED specifier allow multiple processes to open the same file simultaneously, provided that each process uses one of these specifiers when opening the file. The READONLY specifier allows the process read access to the file; the SHARED specifier allows other processes read and write access to the file. If a process opens the file without specifying READONLY or SHARED, no other process can open that file even by specifying READONLY or SHARED.

In the following Fortran segment, if the read operation indicates that the record is locked, the read operation is repeated. You should not attempt to read a locked record without providing a delay (in this example, the call to ERRSNS) to allow the other process time to complete its operation and unlock the record. 


! Status variables and values 
INTEGER STATUS, 
2       IOSTAT, 
2       IO_OK 
PARAMETER (IO_OK = 0) 
INCLUDE '($FORDEF)' 
! Logical unit number 
INTEGER LUN /1/ 
! Record variables 
INTEGER LEN 
CHARACTER*80 RECORD 
   .
   .
   .
READ (UNIT = LUN, 
2     FMT = '(Q,A)' 
2     IOSTAT = IOSTAT) LEN, RECORD (1:LEN) 
IF (IOSTAT .NE. IO_OK) THEN 
  CALL ERRSNS (,,,,STATUS) 
   IF (STATUS .EQ. FOR$_SPERECLOC) THEN 
     DO WHILE (STATUS .EQ. FOR$_SPERECLOC)           
     READ (UNIT = LUN, 
2          FMT = '(Q,A)' 
2          IOSTAT = IOSTAT) LEN, RECORD(1:LEN) 
     IF (IOSTAT .NE. IO_OK) THEN 
           CALL ERRSNS (,,,,STATUS) 
           IF (STATUS .NE. FOR$_SPERECLOC) THEN 
                CALL LIB$SIGNAL(%VAL(STATUS)) 
           END IF 
     END IF 
     END DO 
ELSE 
   CALL LIB$SIGNAL (%VAL(STATUS)) 
   END IF 
END IF 
   .
   .
   .

In Fortran, each time you access a record in a shared file, that record is automatically locked either until you perform another I/O operation on the same logical unit, or until you explicitly unlock the record using the UNLOCK statement. If you plan to modify a record, you should do so before unlocking it; otherwise, you should unlock the record as soon as possible.

28.4 File Access and Mapping

To copy an entire data file from the disk to program variables and back again, either use language I/O statements to read and write the data or use the Create and Map Section (SYS$CRMPSC) system service to map the data. Often times, mapping the file is faster than reading it. However, a mapped file usually uses more virtual memory than one that is read using language I/O statements. Using I/O statements, you have to store only the data that you have entered. Using SYS$CRMPSC, you have to initialize the database and store the entire structure in virtual memory including the parts that do not yet contain data.

28.4.1 Using SYS$CRMPSC

Mapping a file means associating each byte of the file with a byte of program storage. You access data in a mapped file by referencing the program storage; your program does not use I/O statements.

Note
Files created using OpenVMS RMS typically contain control information. Unless you are familiar with the structure of these files, do not attempt to map one. The best practice is to map only those files that have been created as the result of mapping.

To map a file, perform the following operations:

  1. Place the program variables for the data in a common block. Page align the common block at link time by specifying an options file containing the following link option for VAX and Alpha systems:
    For VAX systems, specify the following: 


    PSECT_ATTR = name, PAGE

    For Alpha systems, specify the following: 


    PSECT_ATTR = name, solitary

    The variable name is the name of the common block.
    Within the common block, you should specify the data in order from most complex to least complex (high to low rank), with character data last. This naturally aligns the data, thus preventing troublesome page breaks in virtual memory.

  2. Open the data file using a user-open routine. The user-open routine must open the file for user I/O (as opposed to OpenVMS RMS I/O) and return the channel number on which the file is opened.
  3. Map the data file to the common block.
  4. Process the records using the program variables in the common block.
  5. Free the memory used by the common block, forcing modified data to be written back to the disk file.

Do not initialize variables in a common block that you plan to map; the initial values will be lost when SYS$CRMPSC maps the common block.

28.4.1.1 Mapping a File

The format for SYS$CRMPSC is as follows: 


SYS$CRMPSC [inadr],[retadr],[acmode],[flags],[gsdnam],[ident],[relpag], 
           [chan], [pagcnt],[vbn],[prot],[pfc]

For a complete description of the SYS$CRMPSC system service, see the OpenVMS System Services Reference Manual.

Starting and Ending Addresses of the Mapped Section

On VAX systems, specify the location of the first variable in the common block as the value of the first array element of the array passed by the inadr argument. Specify the location of the last variable in the common block as the value of the second array element.

On Alpha systems, specify the location of the first variable in the common block as the value of the first array element of the array passed by the inadr argument; the second array element must be the address of the last variable in the common block, which is derived by performing a logical OR with the value of the size of a memory page minus 1. The size of the memory page can be retrieved by a call to the SYS$GETSYI system service.

If the first variable in the common block is an array or string, the first variable in the common block is the first element of that array or string. If the last variable in the common block is an array or string, the last variable in the common block is the last element in that array or string.

Returning the Location of the Mapped Section

On VAX systems, SYS$CRMPSC returns the location of the first and last elements mapped in the retadr argument. The value returned as the starting virtual address should be the same as the starting address passed to the inadr argument. The value returned as the ending virtual address should be equal to or slightly more than (within 512 bytes, or 1 block) the value of the ending virtual address passed to the inadr argument.

On Alpha systems, SYS$CRMPSC returns the location of the first and last elements mapped in the retadr argument. The value returned as the starting virtual address should be the same as the starting address passed to the inadr argument. The value returned as the ending virtual address should be equal to or slightly less than (within a single page size) the value of the ending virtual address passed to the inadr argument.

If the first element is in error, you probably forgot to page-align the common block containing the mapped data.

If the second element is in error, you were probably creating a new data file and forgot to specify the size of the file in your program (see Section 28.4.1.3).

Using Private Sections

Specify SEC$M_WRT for the flags to indicate that the section is writable. If the file is new, also specify SEC$M_DZRO to indicate that the section should be initialized to zero.

Obtaining the Channel Number

You must use a user-open routine to get the channel number (see Section 28.4.1.2). Pass the channel number to the chan argument.

On VAX systems, Example 28-1 maps a data file consisting of one longword and three real arrays to the INC_DATA common block. The options file INCOME.OPT page-aligns the INC_DATA common block.

If SYS$CRMPSC returns a status of SS$_IVSECFLG and you have correctly specified the flags in the mask argument, check to see if you are passing a channel number of 0.

Example 28-1 Mapping a Data File to the Common Block on a VAX System 

!INCOME.OPT 
 
PSECT_ATTR = INC_DATA, PAGE

INCOME.FOR 

! Declare variables to hold statistics 
REAL PERSONS_HOUSE (2048), 
2    ADULTS_HOUSE (2048), 
2    INCOME_HOUSE (2048) 
INTEGER TOTAL_HOUSES 
! 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$M_DZRO 
  SEC_LEN = 
!  (address of last - address of first + size of last + 511)/512 
2  ( (%LOC(TOTAL_HOUSES) - %LOC(PERSONS_HOUSE(1)) + 4 + 511)/512 ) 
  OPEN (UNIT=STATS_LUN, 
2       FILE='STATS.SAV', 
2       STATUS='NEW', 
2       INITIALSIZE = SEC_LEN, 
2       USEROPEN = UFO_CREATE) 
END IF 
! Free logical unit number and map section 
CLOSE (STATS_LUN) 
! ******** 
! MAP DATA 
! ******** 
! Specify first and last address of section 
ADDR(1) = %LOC(PERSONS_HOUSE(1)) 
ADDR(2) = %LOC(TOTAL_HOUSES) 
! Map the section 
STATUS = SYS$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

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:

  1. Set the user-file open bit (FAB$V_UFO) in the file access block (FAB) options mask.
  2. Open the file using SYS$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.)
  3. 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$L_STV) and must be returned in a common block.
  4. Return the status of the open operation (SYS$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:

  1. Specify the size of the file---SYS$CRMPSC maps data based on the size of the file. Therefore, when creating a file that is to be mapped, you must specify in your program a file large enough to contain all of the expected data. Figure the size of your database as follows:
  2. Initialize the file when you map it---The blocks allocated to a file might not be initialized and therefore contain random data. When you first map the file, you should initialize the mapped area to zeros by setting the SEC$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 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 Compaq 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:

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

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