MirOS Manual: 09.f77io(PSD)


Introduction to the f77 I/O Library                       PS1:3-1

               Introduction to the f77 I/O Library

                         David L. Wasley

                           J. Berkman

               University of California, Berkeley
                   Berkeley, California 94720

                            ABSTRACT

          The f77 I/O library, libI77.a,  includes  routines
     to  perform  all of the standard types of Fortran input
     and output specified in the ANSI 1978 Fortran standard.
     The  I/O  Library  was  written  originally by Peter J.
     Weinberger at Bell Labs. Where the original implementa-
     tion  was  incomplete,  it  has  been rewritten to more
     closely implement the standard. Where the  standard  is
     vague,  we have tried to provide flexibility within the
     constraints of the UNIX- operating system. A number  of
     logical  extensions and enhancements have been provided
     such as the use of the C stdio library routines to pro-
     vide efficient buffering for file I/O.

     Revised September, 1985

_________________________
- UNIX is a registered trademark of AT&T  Bell  Labora-
tories in the USA and other countries.

Introduction to the f77 I/O Library                       PS1:3-3

1. Fortran I/O

     The requirements of the  ANSI  standard  impose  significant
overhead  on programs that do large amounts of I/O. Formatted I/O
can be very ``expensive'' while direct access binary I/O is  usu-
ally  very  efficient.  Because of the complexity of Fortran I/O,
some general concepts deserve clarification.

1.1. Types of I/O and logical records

     There  are  four  forms  of  I/O:  formatted,   unformatted,
list directed,  and namelist. The last two are related to format-
ted but do not obey all the rules for formatted  I/O.  There  are
two  types  of  ``files'': external and internal and two modes of
access to files: direct and sequential. The definition of a logi-
cal  record  depends upon the combination of I/O form, file type,
and access mode specified by the Fortran I/O statement.

1.1.1. Direct access external I/O

     A logical record in a  direct  access  external  file  is  a
string  of  bytes  of a length specified when the file is opened.
Read and write statements must not specify logical records longer
than the original record size definition. Shorter logical records
are allowed. Unformatted direct writes leave the unfilled part of
the  record undefined. Formatted direct writes cause the unfilled
record to be padded with blanks.

1.1.2. Sequential access external I/O

     Logical records in sequentially accessed external files  may
be  of  arbitrary  and variable length. Logical record length for
unformatted sequential files is determined by the size  of  items
in  the  iolist.  The  requirements of this form of I/O cause the
external physical record size to be somewhat larger than the log-
ical  record size. For formatted write statements, logical record
length is determined by the format statement interacting with the
iolist  at execution time. The ``newline'' character is the logi-
cal record delimiter. Formatted sequential access causes  one  or
more  logical  records  ending  with ``newline'' characters to be
read or written.

1.1.3. List directed and namelist sequential external I/O

     Logical record length for list directed and namelist I/O  is
relatively meaningless. On output, the record length is dependent
on the magnitude of the data items. On input, the  record  length
is  determined  by  the data types and the file contents. By ANSI
definition, a  slash,  ``/'',  terminates  execution  of  a  list
directed   input  operation.  Namelist  input  is  terminated  by
``&end'' or ``$end'' (depending on whether the  character  before
the namelist name was ``&'' or ``$'').

PS1:3-4                       Introduction to the f77 I/O Library

1.1.4. Internal I/O

     The logical record length for an internal read or  write  is
the  length  of  the  character variable or array element. Thus a
simple character variable is a single logical record. A character
variable  array  is similar to a fixed length direct access file,
and obeys the same rules. Unformatted and namelist  I/O  are  not
allowed on ``internal'' files.

1.2. I/O execution

     Note that each execution of a Fortran unformatted I/O state-
ment  causes  a single logical record to be read or written. Each
execution of a Fortran formatted I/O statement causes one or more
logical records to be read or written.

     A slash, ``/'', will terminate assignment of values  to  the
input  list  during  list directed input and the remainder of the
current input line is skipped. The standard is  rather  vague  on
this  point  but  seems  to  require  that a new external logical
record be found at the start of any  formatted  input.  Therefore
data  following  the  slash is ignored and may be used to comment
the data file.

     Direct access list directed I/O is not allowed.  Unformatted
internal  I/O  is  not allowed. Namelist I/O is allowed only with
external sequential files. All other flavors of I/O are  allowed,
although some are not part of the ANSI standard.

     Any I/O statement may include an err= clause to  specify  an
alternative branch to be taken on errors and/or an iostat= clause
to return the specific error code. Any error detected during  I/O
processing  will cause the program to abort unless either err= or
iostat= has been specificed in the program. Read  statements  may
include end= to branch on end-of-file. The end-of-file indication
for that logical unit may be reset with  a  backspace  statement.
File  position  and the value of I/O list items is undefined fol-
lowing an error.

2. Implementation details

     Some details of the current implementation may be useful  in
understanding constraints on Fortran I/O.

2.1. Number of logical units

     Unit numbers must be in the range 0 - 99. The maximum number
of  logical units that a program may have open at one time is the
same as the UNIX system limit, currently 48.

2.2. Standard logical units

     By default,  logical  units  0,  5,  and  6  are  opened  to

Introduction to the f77 I/O Library                       PS1:3-5

``stderr'',  ``stdin'', and ``stdout'' respectively. However they
can be re-defined with  an  open  statement.  To  preserve  error
reporting, it is an error to close logical unit 0 although it may
be reopened to another file.

     If you want to open the default file name  for  any  precon-
nected logical unit, remember to close the unit first. Redefining
the standard units may impair normal console I/O. An  alternative
is  to  use  shell re-direction to externally re-define the above
units. To re-define default blank control or format of the  stan-
dard input or output files, use the open statement specifying the
unit number and no file name (see S2.4).

     The standard units,  0,  5,  and  6,  are  named  internally
``stderr'', ``stdin'', and ``stdout'' respectively. These are not
actual file names and can not be used for  opening  these  units.
Inquire  will  not  return these names and will indicate that the
above units are not named unless they have been  opened  to  real
files.  The names are meant to make error reporting more meaning-
ful.

2.3. Vertical format control

     Simple vertical format control is implemented.  The  logical
unit  must  be  opened  for sequential access with form = 'print'
(see S3.2). Control codes ``0'' and ``1''  are  replaced  in  the
output  file  with  ``\n''  and  ``\f'' respectively. The control
character ``+'' is not implemented and, like any other  character
in the first position of a record written to a ``print'' file, is
dropped. The form = 'print' mode does not recognize vertical for-
mat control for direct formatted, list directed, or namelist out-
put.

     An alternative is to use the filter fpr(1) for vertical for-
mat  control.  It  replaces  ``0'' and ``1'' by ``\n'' and ``\f''
respectively, and implements the ``+'' control code. Unlike  form
=  'print'  which drops unrecognized form control characters, fpr
copies those characters to the output file.

2.4. File names and the open statement

     A file name may be specified in an open  statement  for  the
logical  unit.  If  a logical unit is opened by an open statement
which does not specify a file name, or it is opened implicitly by
the  execution  of  a read, write, or endfile statement, then the
default file name is fort.N where N is the logical  unit  number.
Before  opening  the  file, the library checks for an environment
variable with a name identical to the tail of the file name  with
periods removed.- If it finds such an  environment  variable,  it
uses  its  value  as  the actual name of the file. For example, a
_________________________
-Periods are deleted because they can not  be  part  of
environment variable names in the Bourne shell.

PS1:3-6                       Introduction to the f77 I/O Library

program containing:

        open(32,file='/usr/guest/census/data.d')
        read(32,100) vec
        write(44) vec

normally will read from  /usr/guest/census/data.d  and  write  to
fort.44  in  the  current directory. If the environment variables
datad and fort44 are set, e.g.:

        % setenv datad mydata
        % setenv fort44 myout

in the C shell or:

        $ datad=mydata
        $ fort44=myout
        $ export datad fort44

in the Bourne shell, then the program will read from  mydata  and
write to myout.

     An open statement need not specify a file name. If it refers
to  a  logical  unit  that  is already open, the blank= and form=
specifiers may be redefined without affecting  the  current  file
position.  Otherwise,  if status = 'scratch' is specified, a tem-
porary file with a name of the form tmp.FXXXXXX will  be  opened,
and,  by  default, will be deleted when closed or during termina-
tion of program execution.

     It is an error to try to open an existing file with status =
'new'  .  It  is  an error to try to open a nonexistent file with
status = 'old' . By default, status = 'unknown' will be  assumed,
and a file will be created if necessary.

     By default, files are positioned  at  their  beginning  upon
opening,  but  see  fseek(3f)  and  ioinit(3f)  for alternatives.
Existing files  are  never  truncated  on  opening.  Sequentially
accessed  external  files are truncated to the current file posi-
tion on close, backspace, or rewind only if the  last  access  to
the  file  was a write. An endfile always causes such files to be
truncated to the current file position.

2.5. Format interpretation

     Formats which are in format statements  are  parsed  by  the
compiler; formats in read, write, and print statements are parsed
during execution by the I/O library. Upper as well as lower  case
characters are recognized in format statements and all the alpha-
betic arguments to the I/O library routines.

     If the external representation of a datum is too  large  for
the  field  width  specified,  the specified field is filled with
asterisks (*). On Ew.dEe  output,  the  exponent  field  will  be

Introduction to the f77 I/O Library                       PS1:3-7

filled  with  asterisks  if  the  exponent  representation is too
large. This will only happen if ``e'' is zero (see appendix B).

     On output, a real value that is truly zero will  display  as
``0.''  to  distinguish  it  from a very small non-zero value. If
this causes  problems  for  other  input  systems,  the  BZ  edit
descriptor  may  be used to cause the field following the decimal
point to be filled with zero's.

     Non-destructive tabbing is implemented for both internal and
external  formatted I/O. Tabbing left or right on output does not
affect previously written portions of a record. Tabbing right  on
output  causes  unwritten  portions of a record to be filled with
blanks. Tabbing right off the end of an input logical  record  is
an  error.  Tabbing left beyond the beginning of an input logical
record leaves the input pointer at the beginning of  the  record.
The  format  specifier  T must be followed by a positive non-zero
number. If it is not, it  will  have  a  different  meaning  (see
S3.1).

     Tabbing left requires seek  ability  on  the  logical  unit.
Therefore  it  is not allowed in I/O to a terminal or pipe. Like-
wise, nondestructive tabbing in either direction is possible only
on  a unit that can seek. Otherwise tabbing right or spacing with
X will write blanks on the output.

2.6. List directed output

     In formatting list directed output, the I/O system tries  to
prevent  output  lines  longer  than 80 characters. Each external
datum will be separated by two spaces. List  directed  output  of
complex  values includes an appropriate comma. List directed out-
put distinguishes between real and double  precision  values  and
formats  them  differently.  Output  of  a  character string that
includes ``\n'' is interpreted reasonably by the output system.

2.7. I/O errors

     If I/O errors are not  trapped  by  the  user's  program  an
appropriate  error  message  will be written to ``stderr'' before
aborting. An error number will be printed in ``[ ]'' along with a
brief error message showing the logical unit and I/O state. Error
numbers < 100 refer to UNIX errors,  and  are  described  in  the
introduction  to chapter 2 of the UNIX Programmer's Manual. Error
numbers ≥ 100 come  from  the  I/O  library,  and  are  described
further in the appendix to this writeup=. For internal I/O,  part
of  the string will be printed with ``|'' at the current position
in the string. For external I/O, part of the current record  will
be  displayed  if the error was caused during reading from a file
that can backspace.
_________________________
= On many systems, these are also available in help f77
io_err_msgs.

PS1:3-8                       Introduction to the f77 I/O Library

3. Non-``ANSI Standard'' extensions

     Several extensions have been added to the I/O system to pro-
vide  for  functions  omitted  or poorly defined in the standard.
Programmers should be aware that these are non-portable.

3.1. Format specifiers

     B is an acceptable edit control specifier. It causes  return
to  the logical unit's default mode of blank interpretation. This
is consistent with S which returns to default sign control.

     P by itself is equivalent to 0P . It resets the scale factor
to the default value, 0.

     The form of the Ew.dEe format specifier has been extended to
D also. The form Ew.d.e is allowed but is not standard. The ``e''
field specifies the minimum number of digits  or  spaces  in  the
exponent  field  on  output.  If the value of the exponent is too
large, the exponent notation e or d will be dropped from the out-
put  to  allow  one more character position. If this is still not
adequate, the ``e'' field will be filled with asterisks (*).  The
default value for ``e'' is 2.

     An additional form of tab  control  specification  has  been
added.  The  ANSI  standard  forms TRn, TLn, and Tn are supported
where n is a positive non-zero number. If T or nT  is  specified,
tabbing  will  be  to  the next (or n-th) 8-column tab stop. Thus
columns of alphanumerics can be lined up without counting.

     A format control specifier has been added  to  suppress  the
newline  at  the end of the last record of a formatted sequential
write. The specifier is a dollar sign ($). It is  constrained  by
the same rules as the colon (:). It is used typically for console
prompts. For example:

        write (*, "('enter value for x: ',$)")
        read (*,*) x

     Radices other than 10 can be specified for formatted integer
I/O  conversion.  The  specifier  is patterned after P, the scale
factor for floating point conversion. It remains in effect  until
another  radix is specified or format interpretation is complete.
The specifier is defined as [n]R where 2 ≤ n ≤ 36. If n is  omit-
ted, the default decimal radix is restored.

     The format specifier Om.n may be used for an  octal  conver-
sion;  it  is  equivalent  to  8R,Im.n,10R.  Similarly,  Zm.n  is
equivalent to 16R,Im.n,10R and may be  used  for  an  hexadecimal
conversion;

     In conjunction with the above, a sign control specifier  has

Introduction to the f77 I/O Library                       PS1:3-9

been  added to cause integer values to be interpreted as unsigned
during output conversion. The specifier  is  SU  and  remains  in
effect  until  another  sign control specifier is encountered, or
format  interpretation  is  complete.-  Radix  and   ``unsigned''
specifiers  could  be  used to format a hexadecimal dump, as fol-
lows:

        2000  format ( SU, 8Z10.8 )

3.2. Print files

     The ANSI standard is ambiguous regarding the definition of a
``print''  file.  Since  UNIX  has  no default ``print'' file, an
additional form= specifier is now recognized in the  open  state-
ment.  Specifying  form  =  'print' implies formatted and enables
vertical format control for that logical unit (see S2.3).  Verti-
cal  format  control  is interpreted only on sequential formatted
writes to a ``print'' file.

     The inquire statement will return print in the form=  string
variable  for  logical  units  opened as ``print'' files. It will
return -1 for the unit number of an unconnected file.

     If a logical unit is already open, an open statement includ-
ing  the  form=  option  or the blank= option will do nothing but
re-define those options. This instance of the open statement need
not  include  the  file name, and must not include a file name if
unit= refers to a standard input or  output.  Therefore,  to  re-
define the standard output as a ``print'' file, use:

        open (unit=6, form='print')

3.3. Scratch files

     A close statement with status = 'keep' may be specified  for
temporary  files.  This  is  the  default  for  all  other files.
Remember to get the scratch file's real name, using inquire ,  if
you want to re-open it later.

3.4. List directed I/O

     List directed read has been modified to allow tab characters
_________________________
-Note: Unsigned integer values greater  than  (2**31  -
1),  can be read and written using SU. However they can
not be used in computations because Fortran uses signed
arithmetic  and  such  values  appear to the arithmetic
unit as negative numbers.

PS1:3-10                      Introduction to the f77 I/O Library

wherever blanks are allowed. It also allows input of a string not
enclosed  in  quotes.  The  string must not start with a digit or
quote, and can not contain any separators ( ``,'',  ``/'',  blank
or tab ). A newline will terminate the string unless escaped with
\. Any string not meeting the above restrictions must be enclosed
in quotes (`` " '' or `` ' '').

     Internal list directed  I/O  has  been  implemented.  During
internal  list  reads,  bytes  are  consumed  until the iolist is
satisfied, or the ``end-of-file''  is  reached.  During  internal
list  writes,  records  are filled until the iolist is satisfied.
The length of an internal array element should  be  at  least  20
bytes to avoid logical record overflow when writing double preci-
sion values. Internal list read was implemented to  make  command
line decoding easier. Internal list write should be avoided.

3.5. Namelist I/O

     Namelist I/O is a common extension in Fortran  systems.  The
f77 version was designed to be compatible with other vendors ver-
sions; it is described in ``A Portable Fortran 77 Compiler'',  by
Feldman and Weinberger, August, 1985.

4. Running older programs

     Traditional Fortran  environments  usually  assume  carriage
control  on  all logical units, usually interpret blank spaces on
input as ``0''s, and often  provide  attachment  of  global  file
names to logical units at run time. There are several routines in
the I/O library to provide these functions.

4.1. Traditional unit control parameters

     If a program reads and writes  only  units  5  and  6,  then
including -lI66 in the f77 command will cause carriage control to
be interpreted on output and cause blanks to be  zeros  on  input
without  further modification of the program. If this is not ade-
quate, the routine ioinit(3f) can be called  to  specify  control
parameters  separately,  including  whether files should be posi-
tioned at their beginning or end upon opening.

4.2. Ioinit()

     Ioinit(3f) can be used to attach logical units  to  specific
files  at run time, and to set global parameters for the I/O sys-
tem. It will look for names of  a  user  specified  form  in  the
environment  and  open the corresponding logical unit for sequen-
tial formatted I/O. Names must be of the form PREFIXnn where PRE-
FIX is specified in the call to ioinit and nn is the logical unit
to be opened. Unit numbers < 10 must include the leading ``0''.

     Ioinit should prove adequate for most programs  as  written.
However,  it is written in Fortran-77 specifically so that it may

Introduction to the f77 I/O Library                      PS1:3-11

serve as an example for similar user-supplied  routines.  A  copy
may be retrieved by ``ar x /usr/lib/libU77.a ioinit.f''. See S2.4
for another way to override program file names  through  environ-
ment variables.

5. Magnetic tape I/O

     Because the I/O library uses  stdio  buffering,  reading  or
writing  magnetic  tapes  should  be  done with great caution, or
avoided if possible. A set of routines has been provided to  read
and  write  arbitrary sized buffers to or from tape directly. The
buffer must be a character object. Internal I/O can  be  used  to
fill  or  interpret  the buffer. These routines do not use normal
Fortran I/O processing and do not obey  Fortran  I/O  rules.  See
topen(3f).

6. Caveat Programmer

     The I/O library is extremely complex yet  we  believe  there
are  few  bugs left. We've tried to make the system as correct as
possible according to the ANSI X3.9-1978  document  and  keep  it
compatible  with the UNIX file system. Exceptions to the standard
are noted in appendix B.

PS1:3-12                      Introduction to the f77 I/O Library

                           Appendix A

                   I/O Library Error Messages

     The following  error  messages  are  generated  by  the  I/O
library.  The error numbers are returned in the iostat= variable.
Error numbers < 100 are generated by the  UNIX  kernel.  See  the
introduction  to  chapter  2  of  the UNIX Programmers Manual for
their description.

     100  error in format
          See error message output for the location of the  error
          in  the format. Can be caused by more than 10 levels of
          nested parentheses, or an extremely long format  state-
          ment.

     101  illegal unit number
          It is illegal to close logical  unit  0.  Unit  numbers
          must be between 0 and 99 inclusive.

     102  formatted i/o not allowed
          The logical unit was opened for unformatted I/O.

     103  unformatted i/o not allowed
          The logical unit was opened for formatted I/O.

     104  direct i/o not allowed
          The logical unit was opened for sequential  access,  or
          the logical record length was specified as 0.

     105  sequential i/o not allowed
          The logical unit was opened for direct access I/O.

     106  can't backspace file
          The file associated with the logical unit  can't  seek.
          May be a device or a pipe.

     107  off beginning of record
          The format specified a left tab beyond the beginning of
          an internal input record.

     108  can't stat file
          The system can't return status  information  about  the
          file. Perhaps the directory is unreadable.

     109  no * after repeat count
          Repeat counts in list directed I/O must be followed  by
          an * with no blank spaces.

Introduction to the f77 I/O Library                      PS1:3-13

     110  off end of record
          A formatted write tried to go beyond the  logical  end-
          of-record. An unformatted read or write will also cause
          this.

     111  truncation failed
          The truncation of an external sequential file on close,
          backspace, rewind, or endfile failed.

     112  incomprehensible list input
          List input has to be just right.

     113  out of free space
          The library dynamically creates  buffers  for  internal
          use.  You  ran  out of memory for this. Your program is
          too big!

     114  unit not connected
          The logical unit was not open.

     115  invalid data for integer format term
          Only spaces, a leading sign and digits are allowed.

     116  invalid data for logical format term
          Legal input consists of  spaces  (optional),  a  period
          (optional), and then a ``t'', ``T'', ``f'', or ``F''.

     117  'new' file exists
          You   tried   to   open   an   existing    file    with
          ``status='new'''.

     118  can't find 'old' file
          You  tried   to   open   a   non-existent   file   with
          ``status='old'''.

     119  opening too many files or unknown system error
          Either you are trying to open too many files simultane-
          ously or there has been an undetected system error.

     120  requires seek ability
          Direct access requires seek ability. Sequential  unfor-
          matted I/O requires seek ability on the file due to the
          special data  structure  required.  Tabbing  left  also
          requires seek ability.

     121  illegal argument
          Certain arguments to open, etc.  will  be  checked  for
          legitimacy.  Often  only  non-default  forms are looked
          for.

     122  negative repeat count
          The repeat count for list  directed  input  must  be  a
          positive integer.

PS1:3-14                      Introduction to the f77 I/O Library

     123  illegal operation for unit
          An operation was requested for a device associated with
          the  logical unit which was not possible. This error is
          returned by the tape I/O routines if attempting to read
          past end-of-tape, etc.

     124  invalid data for d, e, f or g format term
          Input data must be legal.

     125  illegal input for namelist
          Column one of input is ignored, the namelist name  must
          match,  the  variables must be in the namelist, and the
          data must be of the right type.

Introduction to the f77 I/O Library                      PS1:3-15

                           Appendix B

                 Exceptions to the ANSI Standard

     A few exceptions to the ANSI standard remain.

Vertical format control

     The ``+'' carriage control specifier  is  not  fully  imple-
mented  (see  S2.3).  It  would  be  difficult  to  implement  it
correctly and still provide UNIX-like file I/O.

     Furthermore, the carriage control  implementation  is  asym-
metrical. A file written with carriage control interpretation can
not be read again with the same characters in column 1.

     An alternative to interpreting carriage  control  internally
is  to  run  the  output file through a ``Fortran output filter''
before printing. This filter could recognize a much broader range
of  carriage  control  and include terminal dependent processing.
One such filter is fpr(1).

Default files

     Files created by  default  use  of  endfile  statements  are
opened  for sequential formatted access. There is no way to rede-
fine such a file to allow direct or unformatted access.

Lower case strings

     It is not clear if the  ANSI  standard  requires  internally
generated  strings to be upper case or not. As currently written,
the inquire statement will return  lower  case  strings  for  any
alphanumeric data.

Exponent representation on Ew.dEe output

     If the field width for the exponent is too small, the  stan-
dard  allows  dropping  the  exponent  character  but only if the
exponent is > 99. This system does not enforce that  restriction.
Further,  the  standard  implies  that  the  entire field, ``w'',
should be filled with  asterisks  if  the  exponent  can  not  be
displayed. This system fills only the exponent field in the above
case since that is more diagnostic.

Pre-connection of files

PS1:3-16                      Introduction to the f77 I/O Library

     The standard says  units  must  be  pre-connected  to  files
before  the program starts or must be explicitly opened. Instead,
the I/O library connects the unit to a file on its first use in a
read,  write,  print,  or endfile statement. Thus inquire by unit
can not tell prior to a unit number use  the  characteristics  or
name of the file corresponding to a unit.

PS1:3-2                       Introduction to the f77 I/O Library

                        Table of Contents

1. Fortran I/O .............................................    3

  1.1. Types of I/O and logical records ....................    3

     1.1.1. Direct access external I/O .....................    3

     1.1.2. Sequential access external I/O .................    3

     1.1.3. List directed and namelist sequential exter-
nal I/O ....................................................    3

     1.1.4. Internal I/O ...................................    4

  1.2. I/O execution .......................................    4

2. Implementation details ..................................    4

  2.1. Number of logical units .............................    4

  2.2. Standard logical units ..............................    4

  2.3. Vertical format control .............................    5

  2.4. File names and the open statement ...................    5

  2.5. Format interpretation ...............................    6

  2.6. List directed output ................................    7

  2.7. I/O errors ..........................................    7

3. Non-``ANSI Standard'' extensions ........................    8

  3.1. Format specifiers ...................................    8

  3.2. Print files .........................................    9

  3.3. Scratch files .......................................    9

  3.4. List directed I/O ...................................    9

  3.5. Namelist I/O ........................................   10

4. Running older programs ..................................   10

  4.1. Traditional unit control parameters .................   10

Introduction to the f77 I/O Library                       PS1:3-3

  4.2. Ioinit() ............................................   10

5. Magnetic tape I/O .......................................   11

6. Caveat Programmer .......................................   11

Appendix A: I/O Library Error Messages .....................   12

Appendix B: Exceptions to the ANSI Standard ................   15

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