12.6 OPEN Statement

The OPEN statement connects an external file to a unit, creates a new file and connects it to a unit, creates a preconnected file, or changes certain properties of a connection.

The OPEN statement takes the following form:

OPEN ([UNIT=]io-unit [, FILE=name] [, ERR=label] [, IOSTAT=i-var], slist)

io-unit
Is an external unit specifier.

name
Is a character or numeric expression specifying the name of the file to be connected. For more information, see Section 12.6.14.

label
Is the label of the branch target statement that receives control if an error occurs.

i-var
Is a scalar integer variable that is defined as a positive integer if an error occurs and zero if no error occurs.

slist
Is one or more OPEN specifiers in the form specifier = value or specifier. Each specifier can appear only once.

The OPEN specifiers and their acceptable values are summarized in Table 12-1.

The OPEN specifiers are described individually in the following sections. The control specifiers that can be specified in an OPEN statement (UNIT, ERR, and IOSTAT) are discussed in Section 10.2.1.

Table 12-1 OPEN Statement Specifiers and Values on OpenVMS Systems

   c_expr: A scalar default character expression
   dr:     A direction, ASCENDING or DESCENDING
   dt:     A data type, INTEGER or CHARACTER
   e1:     The first byte position of a key
   e2:     The last byte position of a key 
   func:   An external function
   label:  A statement label
   n_expr: A scalar numeric expression
   var:    A scalar integer variable

Rules and Behavior

The control specifiers ([UNIT=]io-unit, ERR=label, and IOSTAT=i-var) and OPEN specifiers can appear anywhere within the parentheses following OPEN. However, if the UNIT specifier is omitted, the io-unit must appear first in the list.

Specifier values that are scalar numeric expressions can be any integer or real expression. The value of the expression is converted to integer data type before it is used in the OPEN statement.

Only one unit at a time can be connected to a file, but multiple OPENs can be performed on the same unit. If an OPEN statement is executed for a unit that already exists, the following occurs:

• If FILE is not specified, or FILE specifies the same file name that appeared in a previous OPEN statement, the current file remains connected.

  If the file names are the same, the values for the BLANK, CARRIAGECONTROL, CONVERT, DELIM, DISPOSE, ERR, IOSTAT, and PAD specifiers can be changed. Other OPEN specifier values cannot be changed, and the file position is unaffected.

• If FILE specifies a different file name, the previous file is closed and the new file is connected to the unit.

The ERR and IOSTAT specifiers from any previously executed OPEN statement have no effect on any currently executing OPEN statement. If an error occurs, no file is opened or created.

Secondary operating system messages do not display when IOSTAT is specified. To display these messages, remove IOSTAT or use a platform-specific method. (For more information, see your user manual.)

Examples

You can specify character values at run time by substituting a character expression for a specifier value in the OPEN statement. The character value can contain trailing blanks but not leading or embedded blanks; for example:

  CHARACTER*7 QUAL /' '/
  ...
  IF (exp) QUAL = '/DELETE'
    OPEN (UNIT=1, STATUS='NEW', DISP='SUBMIT'//QUAL)

  OPEN (UNIT=1, STATUS='NEW', ERR=100)

The following statement creates a 50-block direct access file for temporary storage. The file is deleted at program termination.

  OPEN (UNIT=3, STATUS='SCRATCH', ACCESS='DIRECT',              &
       INITIALSIZE=50, RECL=64)

 OPEN (UNIT=I, FILE='MTA0:MYDATA.DAT', BLOCKSIZE=8192,
1     STATUS='NEW', ERR=14, RECL=1024,
1     RECORDTYPE='FIXED')

The following statement opens the file (created in the previous example) for input:

 OPEN (UNIT=I, FILE='MTA0:MYDATA.DAT', READONLY,
1     STATUS='OLD', RECL=1024, RECORDTYPE='FIXED',
1     BLOCKSIZE=8192)

The following statement uses the file name supplied by the user and the default file specification supplied by the DEFAULTFILE specifier to define the file specification for an existing file:

 TYPE *, 'ENTER NAME OF DOCUMENT'
 ACCEPT *, DOC
 OPEN (UNIT=1, FILE=DOC, DEFAULTFILE='[ARCHIVE].TXT',
1     STATUS='OLD')

For More Information:

• On Fortran IOSTAT errors, see your user manual.
  
  
• On the UNIT control specifier, see Section 10.2.1.1.
  
  
• On the ERR control specifier, see Section 10.2.1.8.
  
  
• On the IOSTAT control specifier, see Section 10.2.1.7.
  
  
• On using the INQUIRE statement to get file attributes of existing files, see Section 12.5.
  
  
• On OPEN statements and file connection, see your user manual.