Operations on external files

Once again, this is an overview only.

File positioning statements

The open statement

The statement is used to connect an external file to a unit, create a file that is preconnected, or create a file and connect it to a unit. The syntax is

open (unit=u, status=st, action=act[, olist])

where olist is a list of optional specifiers. The specifiers may appear in any order.

open (unit=2, iostat=ios, file="cities", status="new", access="direct", &
      action="readwrite", recl=100)

Other specifiers are form and position.

The close statement

This is used to disconnect a file from a unit.

close (unit=u[, iostat=ios] [, status=st])

as in

close (unit=2, iostat=ios, status="delete")

The inquire statement

At any time during the execution of a program it is possible to inquire about the status and attributes of a file using this statement.

Using a variant of this statement, it is similarly possible to determine the status of a unit, for instance whether the unit number exists for that system.

Another variant permits an inquiry about the length of an output list when used to write an unformatted record.

For inquire by unit

inquire (unit=u, ilist)

or for inquire by file

inquire (file=fln, ilist)

or for inquire by I/O list

inquire (iolength=length) olist

As an example

logical            :: ex, op
character(len=11)  :: nam, acc, seq, frm
integer            :: irec, nr
inquire (unit=2, exist=ex, opened=op, name=nam, access=acc, sequential=seq, &
         form=frm, recl=irec, nextrec=nr)

yields

ex      .true.
op      .true.
nam      cities
acc      direct
seq      no
frm      unformatted
irec     100
nr       1

(assuming no intervening read or write operations).

Other specifiers are iostat, opened, number, named, formatted, position, action, read, write, readwrite.