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4 Input and Output

• 4.1 File Access Methods
  • 4.1.1 Standard Preconnected Units
• 4.2 Opening and Closing Files
  • 4.2.1 Direct Access Files
  • 4.2.2 Closing a File
• 4.3 Unformatted Data Transfer
• 4.4 Formatted Data Transfer
  • 4.4.1 Implied DO List Input Output List
  • 4.4.2 Format Specifications
    • A Format Control Character Data
    • D Format Control Real Double Precision Data with Exponent
    • E Format Control Real Single Precision Data with Exponent
    • F Format Control - Real Single Precision Data
    • G Format Control Real Data
    • I Format Control Integer Data
    • L Format Control Logical Data
    • Quote Format Control
    • BN Format Control Blank Control
    • H Format Control Hollerith Control
    • Octal and Hexadecimal Values O and Z
    • P Format Specifier Scale Control
    • Q Format Control - Quantity
    • S Format Control Sign Control
    • T , TL and X Format Controls Spaces and Tab Controls
    • Slash Format Control / End of Record
    • The : Format Specifier Format Termination
    • $ Format Control
  • 4.4.3 Variable Format Expressions <expr>
• 4.5 List-directed formatting
  • 4.5.1 List-directed input
  • 4.5.2 List-directed output
  • 4.5.3 Commas in External Field
• 4.6 Namelist Groups
  • 4.6.1 Namelist Input
  • 4.6.2 Namelist Output

Input, output, and format statements provide the means for transferring data to or from files. Data is transferred as records to or from files. A record is a sequence of data which may be values or characters and a file is a sequence of such records. A file may be internal, that is, held in memory, or external such as those held on disk. To access an external file a formal connection must be made between a unit, for example a disk file, and the required file. An external unit must be identified either by a positive integer expression, the value of which indicates a unit, or by an asterisk (*) which identifies the standard input or output device.

This chapter describes the types of input and output available and provides examples of input, output and format statements. There are four types of input/output you can use to transfer data to or from files: unformatted, formatted, list directed, and namelist.

• unformatted data is transferred between the item(s) in the input/output list (iolist) and the current record in the file. Exactly one record may be read or written.
• formatted data is edited to conform to a format specification, and the edited data is transferred between the item or items in the iolist, and the file. One or more records may be read or written.
• list directed input/output is an abbreviated form of formatted input/output that does not require the use of a format specification. Depending on the type of the data item or data items in the iolist, data is transferred to or from the file, using a default, and not necessarily accurate format specification.
• namelist input/output is a special type of formatted data transfer; data is transferred between a named group (namelist group) of data items and one or more records in a file.

4.1 File Access Methods

You can access files using one of two methods, sequential access, or direct access (random access). The access method is determined by the specifiers supplied when the file is opened using the OPEN statement. Sequential access files are accessed one after the other, and are written in the same manner. Direct access files are accessed by specifying a record number for input, and by writing to the currently specified record on output.

Files may contain one of two types of records, fixed length records or variable length records. To specify the size of the fixed length records in a file, use the RECL specifier with the OPEN statement. RECL sets the record length in bytes .[*] RECL can only be used when access is direct.

A record in a variable length formatted file is terminated with \n (on DOS systems a \c\n terminates). A record in a variable length unformatted file is preceded and followed by a word indicating the length of the record.

4.1.1 Standard Preconnected Units

Certain input and output units are predefined, depending on the value of compiler options. The pgf77 option -Mdefaultunit tells the compiler to treat "*" as a synonym for standard input for reading and standard output for writing. When the option is set to -Mnodefaultunit, then the compiler treats "*" as a synonym for unit 5 on input and unit 6 on output.

4.2 Opening and Closing Files

The OPEN statement establishes a connection to a file. OPEN allows you to do any of the following

• Connect an existing file to a unit.
• Create and connect a file to a unit.
• Create a file that is preconnected.
• Establish the access method and record format for a connection.

OPEN (list)

[UNIT]= u

In addition list may contain one of each of the specifiers shown in Table 4-1.

4.2.1 Direct Access Files

If a file is connected for direct access using OPEN with ACCESS='DIRECT', the record length must be specified using RECL=, and optionally one of each of the other specifiers may be used.

Any file opened for direct access must be via fixed length records.

In the following example a new file, book.dat, is created and connected to unit 12 for direct formatted input/output with a record length of 98 characters. Numeric values will have blanks ignored and the variable E1 will be assigned some positive value if an error condition exists when the OPEN statement is executed; execution will then continue with the statement labeled 20. If no error condition pertains, E1 is assigned the value 0 and execution continues with the statement following the OPEN statement.

OPEN(12,IOSTAT=E1,ERR=20,FILE='book.dat',BLANK='NULL',
+ACCESS='DIRECT',RECL=98,FORM='FORMATTED',STATUS='NEW')



Specifier


Description


IOSTAT=
ios


Input/output
status specifier where ios is an integer scalar memory reference.  If
this is included in list, ios becomes defined with 0 if no error
exists or a positive integer when there is an error condition.


ERR=
errs


An
error specifier which takes the form of a statement label of an executable
statement in the same program. If an error condition occurs, execution
continues with the statement specified by errs..


FILE=
fin


Where
fin is a character string defining the file name to be connected to the
specified unit.


STATUS=
sta


The
file status where sta is a character expression: it can be NEW, OLD,
SCRATCH or UNKNOWN. When OLD or NEW is specified a file specifier must be
given. SCRATCH must not be used with a named file. The default is UNKNOWN.


ACCESS=
 acc


Where
acc is a character string specifying the access method for file connection
as DIRECT (random access) or SEQUENTIAL. The default is SEQUENTIAL.


FORM=
fm


Where
fm is a character string specifying whether the file is being connected for
FORMATTED or UNFORMATTED output respectively. The default is FORMATTED.


RECL=
rl


Where
rl is an integer which defines the record length in a file connected for
direct access and is the number of characters when formatted input/output is
specified. This specifier must only be given when a file is connected for
direct access.


BLANK=
blnk


Where
blnk is a character string which takes the value NULL or ZERO: NULL causes
all blank characters in numeric formatted input fields to be ignored with the
exception of an all blank field which has a value of zero. ZERO causes all
blanks other than leading blanks to be treated as zeros. The default is NULL.
This specifier must only be used when a file is connected for formatted
input/output.



4.2.2 Closing a File



Close
a unit by specifying the CLOSE statement from within any module. If the unit
specified does not exist or has no file connected to it, the CLOSE statement
has no effect. 

Provided the file is still in existence it may be reconnected to the same or a
different unit after the execution of a CLOSE statement. An implicit CLOSE is
executed when a program stops.

The CLOSE statement terminates the connection of the specified file to a unit.

CLOSE ([UNIT=] u [,IOSTAT=ios] [,ERR= errs ] 
	[,STATUS= sta] [,DISPOSE= sta] [,DISP= sta])

Close
takes the status values IOSTAT, ERR, and STATUS, similar to those described in
Table 4-1  OPEN Specifiers. In addition, CLOSE allows the DISPOSE or DISP
specifier which can take a status value sta which is a character string,
where case is insignificant, specifying the file status (the same keywords are
used for the DISP and DISPOSE status). Status can be can be KEEP or DELETE.
KEEP cannot be specified for a file whose dispose status is SCRATCH. When KEEP
is specified (for a file that exists) the file continues to exist after the
CLOSE statement, conversely DELETE deletes the file after the CLOSE statement.
The default value is KEEP unless the file status is SCRATCH.

A unit may be the subject of a CLOSE statement from within any module. If the
unit specified does not exist or has no file connected to it the use of the
CLOSE statement has no effect. Provided the file is still in existence it may
be reconnected to the same or a different unit after the execution of a CLOSE
statement. Note that an implicit CLOSE is executed when a program stops.

In the following example the file on UNIT 6 is closed and deleted.

CLOSE(UNIT=6,STATUS='DELETE')



4.3 Unformatted Data Transfer



Unformatted
data transfer allows data to be transferred between the current record and the
items specified in an input/output list. Use OPEN to open a file for
unformatted output:

OPEN (2, FILE='new.dat', FORM='UNFORMATTED')

The
unit specified must be an external unit. 

After data is transferred, the file is positioned after the last record read or
written, if there is no error condition or end-of-file condition set
Unformatted data transfer cannot be carried out if the file is connected for
formatted input/output.

The following example shows an unformatted input statement: 

READ (2, ERR=50) A, B

On
output to a file connected for direct access, the output list must not specify
more values than can fit into a record. If the values specified do not fill the
record the rest of the record is undefined. 

On input the following conditions must pertain; the file must be positioned so
that the record read is either:

	An unformatted record or an endfile record.
	The number of values required by the input list in the input statement
must be less than or equal to the number of values in the record being read.
The type of each value in the record must agree with that of the corresponding
entity in the input list. However one complex value may correspond to two real
list entities or vice versa. If the input list item is of type CHARACTER, its
length must be the same as that of the character value
	In the event of an error condition, the position of the file is
indeterminate.

4.4 Formatted Data Transfer



During
formatted data transfer, data is edited to conform to a format specification,
and the edited data is transferred between the items specified in the input or
output statement's iolist and the file; the current record is read or
written and, possibly, additional records. On input the file must be positioned
so that the record read is either a formatted record or an endfile record.
Formatted data transfer is prohibited if the file is connected for unformatted
input/output.

For variable length record formatted input, each newline character is
interpreted as a record separator. On output, the I/O system writes a newline
at the end of each record. If a program writes a newline itself, the single
record containing the newline will appear as two records when read or
backspaced over. The maximum allowed length of a record in a variable length
record formatted file is 2000 characters.[*] 

4.4.1 Implied DO List Input Output List



An
implied DO list takes the form

(iolist,do-var=var1,var2,var3)

where
the items in iolist are either items permissible in an input/output list
or another implied DO list,. The value do-var is an INTEGER, REAL
or DOUBLE PRECISION variable and var1, var2 and var3 are
arithmetic expressions of type INTEGER, REAL or DOUBLE PRECISION. Generally
do-var, var1, var2 and var3 are of type INTEGER.
Should iolist occur in an input statement, the do-var cannot be
used as an item in iolist.  If var3 and the preceding comma are
omitted the increment takes the value 1. The list items are specified once for
each iteration of the DO loop with the DO-variable being substituted as
appropriate. 

REAL C(6),D(6)
DATA OXO,(C(I),I=7,9),TEMP,(D(J),J=1,2)/4*0.0,3*10.0/

In
the above example OXO, C(7), C(8) and C(9) are set to 0.0 with TEMP,
D(1) and D(2) being set to 10.0. In the next example:

READ *,A,B,(R(I),I=1,4),S

has
the same effect as

READ *,A,B,R(1),R(2),R(3),R(4),S



4.4.2 Format Specifications



Format
requirements may be given either in an explicit FORMAT statement or
alternatively, as fields within an input/output statement (as values in
character variables, arrays or other character expressions within the
input/output statement).

When a format identifier in a formatted input/output statement is a character
array name or other character expression, the leftmost characters must be
defined with character data that constitute a format specification when the
statement is executed. A character format specification is enclosed in
parentheses. Blanks may precede the left parenthesis. Character data may follow
the right-hand parenthesis and has no effect on the format specification. When
a character array name is used as a format identifier, the length of the format
specification can exceed the length of the first element of the array; a
character array format specification is considered to be an ordered
concatenation of all the array elements. When a character array element is used
as a format identifier the length must not exceed that of the element used. 

The FORMAT statement has the form:

FORMAT (list-of-format-requirements)

The
list of format requirements can be any of the following, separated by commas:

	Repeatable editor commands which may or may not be preceded by an integer
constant which defines the number of repeats.
	Non-repeatable editor commands.
	A format specification list enclosed in parentheses, optionally preceded
by an integer constant which defines the number of repeats.
Each action of
format control depends on a FORMAT specified edit code and the next item in the
input/output list used. If an input/output list contains at least one item
there must be at least one repeatable edit code in the format specification. An
empty format specification FORMAT( ) can only be used if no list items are
specified - in such a case one input record is skipped or an output record
containing no characters is written. Unless the edit code or the format list is
preceded by a repeat specification, a format specification is interpreted from
left to right. When a repeat specification is used, the appropriate item is
repeated the required number of times.

Each repeatable edit code has a corresponding item in the iolist;
however when a list item is of type complex two edit codes of F, E, D or G are
required. The edit codes P, X, T, TL, TR, S, SP, SS, H, BN, BZ, /, : and
apostrophe act directly on the record and have no corresponding item in the
input/output list.

The file is positioned after the last character read or written when the edit
codes I, F, E, D, G, L, A, H or apostrophe are processed. If the specified unit
is a printer then the first character of the record is used to control the
vertical spacing as shown in Table 4-2:



Character



Vertical
Spacing


Blank


One
line


0



Two
lines


1



To
first line on next page


+



No
advance



A Format Control  Character Data


The
A specifier transfers characters. The A can optionally be followed by a field
width w. When w is not specified, the width is determined by the
size of the data item.

On output, if l is the length of the character item and w is the
field width, then the following rules apply:

If w > l	w - l blanks before the character

If w < l	leftmost w characters.

On input, if l is the length of the character io item and w is
the field width, then the following rules apply:

If w > l	rightmost l characters from the input filed.

If w < l	leftmost w characters from the input filed and
followed by l - w blanks.

You can also use the A format specifier to process data types other than
CHARACTER. For types other than CHARACTER, the number of characters supplied
for input/output will equal the size in bytes of the data allocated to the data
type. For example, an INTEGER*4 value is represented with 4 characters and a
LOGICAL*2 is represented with 2 characters.

The following shows a simple example that reads two CHARACTER arrays from the
file data.src: 

   CHARACTER STR1*8, STR2*12
   OPEN(2, FILE='data.src')
   READ(2, 10) STR1, STR2
10 FORMAT ( A8, A12 )



D Format Control  Real Double Precision Data with Exponent


The
D specifier transfers real values for double precision data with a
representation for an exponent. The form of the D specifier is:

Dw.d 

where
w is the field width and d the number of digits in the fractional
part. 

For input, the same conditions apply as for the F specifier which is described
later.

For output the scale factor k controls the decimal normalization. The scale
factor k is the current scale factor specified by the most recent P format
control; if one hasn't been specified, the default is zero (0). If  -d
< k <= 0,  the output file contains leading zeros and
d-|k| significant digits after the decimal point. If 0 < k <
d+2 there are exactly |k| significant digits to the left of the
decimal point and d-k+1 significant digits to the right of the decimal
point. Other values of k are not allowed.

For example:

   DOUBLE PRECISION VAL1
   VAL1 = 141.8835
   WRITE( *, 20) VAL1
20 FORMAT ( D10.4 )

produces
the following:

0.1418D+03



E Format Control  Real Single Precision Data with Exponent


The
E specifier transfers real values for single precision data with an exponent.
The E format specifier has two basic forms:

Ew.d   
Ew.dEe

w
 is the field width, d the number of digits in the fractional part and
e the number of digits to be printed in the exponent part.

For input the same conditions apply as for F editing. For output the scale
factor controls the decimal normalization as in D above.

F Format Control - Real Single Precision Data


The
F specifier transfers real values The form of the F specifier is:

Fw.d

w
is the field width and d is the number of digits in the fractional
part.

On input if the field does not contain a decimal digit or an exponent,
righthand d digits, with leading zeros, are interpreted as being the
fractional part.

On output a leading zero is only produced to the left of the decimal point if
the value is less than one.

G Format Control  Real Data


The
G format specifier has two basic forms:

Gw.d  
Gw.dEe 

The
specifier transfers real values; it acts like the F format control on input and
depending on the value's magnitude, like E or F on output. The magnitude of the
data determines the output format.  For details on the actual format used,
based on the magnitude, refer to Section 13.5.9.2.3 "G Editing", in the ANSI
FORTRAN Standard.

I Format Control  Integer Data


The
I format specifier transfers integer values. The I format specifier has two
basic forms:

Iw
Iw.m

where
w is the field width and m is the minimum filed width on output,
including leading zeros. If present,  m must not exceed width w.

On input, the external field to be input must contain (unsigned) decimal
characters only. An all blank field is treated as a value of zero. If the value
of the external field exceeds the range of the corresponding list element, an
error occurs.

On output, the I field descriptor transfers the decimal values of the
corresponding I/O list element, right-justified, to an external field that is
w characters long. If the value to be transmitted does not fill the
field, leading spaces are inserted; if the value is too large for the field,
the entire field is filled with asterisks. If m is present, the external
field consists of at least m digits, and is zero-filled on the left if
necessary. Note that if m is zero, and the internal representation is
zero, the external field is blank-filled.

L Format Control  Logical Data




Lw

The
L format control transfers logical data of field width w. On input the
list item will become defined with a logical value; the field consists of
optional blanks, followed by an optional decimal point followed by T or F.
Also, the values .TRUE. or .FALSE. may appear in the input field 

The output field consists of w-1 blanks followed by T or F as appropriate.

Quote Format Control 


Quote
editing prints a character constant. The format specifier writes the characters
enclosed between the quotes and cannot be used on input. The field width is
that of the characters contained within quotes (you can also use apostrophes to
enclose the character constant). 

To write an apostrophe (or quote) use two consecutive apostrophes (or
quotes).

For example:

	 WRITE ( *, 101)
101 FORMAT ( 'Print an apostrophe '' and end.')

Produces:

Print an apostrophe ' and end.

Similarly,
you can use quotes, for example:

	 WRITE ( *, 102)
102 FORMAT ( "Print a line with a "" and end.")

Produces:

Print a line with a " and end.



BN Format Control  Blank Control


The
BN and BZ formats control blank spacing. BN causes all embedded blanks except
leading blanks in numeric input to be ignored, which has the effect of right
justifying the remainder of the field. Note that a field of all blanks has the
value zero. Only input statements and I, F, E, D and G editing are affected.

BZ causes all blanks except leading blanks in numeric input to be replaced by
zeros. Only input statements and I, F, E, D and G editing are affected.

H Format Control  Hollerith Control


The
H format control writes the n characters following the H in the format
specification and cannot be used on input.

The basic form of this format specification is:

nHc1cn...

where
n is the number of characters to print and c1 through cn are the
characters to print.

Octal and Hexadecimal Values  O and Z


The
O and Z field descriptors transfer octal or hexadecimal values and can be used
with any data type. They have the form:

Ow[.m] and Zw[.m]

where
w specifies the field width and m indicates minimum field width
on output.

On input, the external field to be input must contain (unsigned) octal or
hexadecimal characters only. An all blank field is treated as a value of zero.
If the value of the external field exceeds the range of the corresponding list
element, an error occurs.

On output, the O and Z field descriptors transfer the octal and hexadecimal
values, respectively, of the corresponding I/O list element, right-justified,
to an external field that is w characters long. If the value to be
transmitted does not fill the field, leading spaces are inserted; if the value
is too large for the field, the entire field is filled with asterisks. If
m is present, the external field consists of at least m digits,
and is zero-filled on the left if necessary. Note that if m is zero, and
the internal representation is zero, the external field is blank-filled.

P Format Specifier  Scale Control



kP


The
P format specifier is the scale factor format which is applied as follows.

	With F, E, D and G editing on input and F editing on output, the external
number equals the internal number multiplied by  10**k . If there is an
exponent in the field on input editing with F, E, D and G the scale factor has
no effect. 
	On output with E and D editing the basic real constant part of the number
is multiplied by 10**k and the exponent reduced by k , and with G editing the
effect of the scale factor is suspended unless the size of the datum to be
edited is outside the range permitted for F editing. If E editing is required
the scale factor has the same effect as with E output editing.
The
following is an example using a scale factor.

		DIMENSION A(6)
		DO 10 I = 1,6
10	A(I) = 25.
		TYPE 100,A
100	FORMAT(' ',F8.2,2PF8.2,F8.2) 

produces:

25.00 2500.00  2500.00  2500.00  2500.00  2500.00

Note
that the effect of the scale factor continues until another scale factor is used.

Q Format Control - Quantity 


The
Q edit descriptor calculates the number of characters remaining in the input
record and stores that value in the next I/O list item. On output, the Q
descriptor skips the next I/O item. 

S Format Control  Sign Control


The
S format specifier restores the default processing for writing a plus; the
default is SS processing.

SP forces the processor to write a plus in any position where an optional plus
is found in numeric output fields, this only affects output statements.

SS stops the processor from writing a plus in any position where an optional
plus is found in numeric output fields, this only affects output statements.

T , TL and X Format Controls  Spaces and Tab Controls


The
T specifier controls which portion of a record a iolist value is read
from or written to a file. The general form is as follows:

Tn

this
specifies that the nth value is to be written to or from a record.

The TL form specifies the relative position to the left of the data to be read
or written.

TLn 

This
specifies that the nth character to the left of the current position is
to be written to or from the record. If the current position is less than or
equal to n the transmission will begin at position one of the record.

The TR form specifies the relative position to the right of the data to be read
or written.

TRn 

Specifies
that the nth character to the right of the current position is to be
written to or from the record. 

The X control specifies a number of characters to skip forward.

nX

Specifies
that the next character to be written to or from is n characters forward
from the current position.

The following example uses the X format specifier.

NPAGE = 19
WRITE ( 6, 90) NPAGE
90 FORMAT('1PAGE NUMBER ,I2, 16X, 'SALES REPORT, Cont.')

produces:

PAGE NUMBER 19                SALES REPORT, Cont.

The
following example shows use of the T format specifier.

   PRINT 25
25 FORMAT (T41,'COLUMN 2',T21,'COLUMN 1')

produces:

         COLUMN 1    COLUMN 2



Slash Format Control /  End of Record


The
slash (/) control indicates the end of data transfer on the current record. 

On input from a file connected for sequential access the rest of the current
record is skipped and the file positioned at the start of the next record.

On output a new record is created which becomes the last and current record.
For an internal file, connected for direct access the record is filled with
blank characters. If a direct access file, the record number is increased by
one and the file is positioned at the start of the record.

The :  Format Specifier  Format Termination


The(:
) control terminates format control if there are no more items in the
input/output list. It has no effect if there are any items left in the list.

$ Format Control


The
$ field descriptor allows the programmer to control carriage control
conventions on output. It is ignored on input. For example, on terminal output,
it can be used for prompting. 

The form of the $ field descriptor is: 

$



4.4.3 Variable Format Expressions <expr>



Variable
format expressions are supported. They provide a means for substituting
run-time expressions for the field width, other parameters for the field and
edit descriptors in a FORMAT statement (except for the H field descriptor and
repeat counts). 

Variable format expressions are enclosed in "<" and ">" and are evaluated
each time they are encountered in the scan of a format. If the value of a
variable used in the expression changes during the execution of the I/O
statement, the new value is used the next time the format item containing the
expression is processed.

4.5 List-directed formatting



List-directed
formatting is an abbreviated form of input/output that does not require the use
of a format specification. The type of the data is used to determine how a
value is read/written. On output it will not always be accurate enough for
certain ranges of values. The characters in a list-directed record constitute a
sequence of values which cannot contain embedded blanks except those permitted
within a character string. To use list-directed input/output formatting,
specify a * for the list of format requirements. For example, the following
example uses list-directed output:

READ( 1, * ) VAL1, VAL2



4.5.1 List-directed input



The
form of the value being input must be acceptable for the type of item in the
iolist. Blanks must not be used as zeros nor be embedded in constants
except in a character constant or within a type complex form contained in
parentheses.




Input
List Type 


Form



Integer


A
numeric input field.


Real



A
numeric input field suitable for F editing with no fractional part unless a
decimal point is used. 


Double
precision 


Same
as for real.


Complex



An
ordered pair of numbers contained within parentheses as shown (real part,
imaginary part).


Logical



A
logical field without any slashes or commas.


Character


A
non-empty character string within apostrophes. A character constant can be
continued on as many records as required. Blanks, slashes and commas can be
used.


A null value has no effect on the definition status of the corresponding
iolist item. A null value cannot represent just one part of a complex
constant but may represent the entire complex constant. A slash encountered as
a value separator stops the execution of that input statement after the
assignment of the previous value. If there are further items in the list they
are treated as if they are null values.

Commas may be used to separate the input values. If there are consecutive
commas, or the if the first non-blank character of a record is a comma, the
input value is a null value.  Input values may also be repeated. 

In the following example of list-directed formatting, assume that 

A= -1.5
K= 125

and
all other variables are undefined. When the statement below reads in the list
from the input file:

READ * I, J, X, Y, Z, A, C, K

where
the file contains the following record:

10,-14,25.2,-76,313,,29/

The
variables are assigned the following values by the list-directed input/output
mechanism:

I=10 
J=-14 
X=25.2 
Y=-76.0 
Z=313.0 
A=-1.5
C=29 
K=125.

Note
that the value for A does not change because the input record is null
(consecutive commas). No input is read for K, so it assumes null and K retains
it previous value ( the / terminates the input).

4.5.2 List-directed output



List directed input/output is an abbreviated form of formatted
input/output that does not require the use of a format specification. Depending
on the type of the data item or data items in the iolist, data is
transferred to or from the file, using a default, and not necessarily accurate
format specification. The data type of each item appearing in the iolist
is formatted according to the rules in Table 4-4.




Data
Type


Default
Formatting



BYTE




I5




INTEGER*2




I7




INTEGER*4




I12




INTEGER*8




I24 




LOGICAL*1




I5 (L2)




LOGICAL*2




L2




LOGICAL*4




L2




LOGICAL*8




L2 




REAL*4




G15.7e2




REAL*8




G25.16e3




COMPLEX*8




(G15.7e2, G15.7e2)




COMPLEX*16




(G25.16e3, G25.16e3)




CHAR *n




An


This
format is applied when the option -Munixlogical is selected when
compiling.

The length of a record is less than 80 characters; if the output of an item
would cause the length to exceed 80 characters, a new record is created. 

Notes

	New records may begin as necessary but, with the exception of character
and complex constants
	Logical output constants are T for true and F for false. 
	Complex constants are contained within parentheses with the real and
imaginary parts separated by a comma. 
	Character constants are not delimited by apostrophes and have each
internal apostrophe (if any are present) represented externally by one
apostrophe 
	Each output record begins with a blank character to provide carriage
control when the record is printed.
	A typeless value output with list-directed I/O is output in hexadecimal
form by default. There is no other octal or hexadecimal capability with
list-directed I/O.

4.5.3 Commas in External Field



Use of the comma in an external field eliminates the need to "count
spaces" to have data match format edit descriptors. The use of a comma to
terminate an input field and thus avoid padding the field is fully
supported. 

4.6 Namelist Groups



The
NAMELIST statement allows for the definition of namelist groups. A namelist
group allows for a special type of formatted input/output, where data is
transferred between a named group of data items defined in a NAMELIST statement
and one or more records in a file.

The general form of a namelist statement is:

	NAMELIST /group-name/ namelist [[,] /group-name/ namelist ]...


where:
group-name
is the name of the namelist group.
namelist
is the list of variables in the namelist group.

4.6.1 Namelist Input



Namelist input is accomplished using a READ statement by specifying a
namelist group as the input item. The following statement shows the format:

     READ  ([unit=] u, [NML=] namelist-group  [,control-information])

One
or more records are processed which define the input for items in the namelist
group.

The records are logically viewed as follows:

$group-name	item=value	[,item=value].... $ [END]

The
following rules describe these input records:

	The start or end delimiter ($) may be an &.
	The start delimiter must begin in column 2 of a record.
	The group-name begins immediately after the start delimiter.
	The spaces or tabs may not appear within the group-name, within any
item, or within any constants.
	The value may be constants as are allowed for list directed input,
or they may be a list of constants separated by commas (,  ) . A list of items
is used to assign consecutive values to consecutive elements of an array.
	Spaces or tabs may precede the item, the = and the constants.
	Array items may be subscripted.
	Character items may be substringed.

4.6.2 Namelist Output



Namelist output is accomplished using a READ statement by specifying a
namelist group as the output item. The following statement shows the format:

@   WRITE  ([unit=] u, [NML=] namelist-group  [,control-information])

The
records output are logically viewed as follows:

 $group-name	
  item = value	
$ [END]

The
following rules describe these output records:

	One record is output per value.
	Multiple values are separated by (, ) .
	Values are formatted according to the rules of the list-directed write.
Exception: character items are delimited by an apostrophe.
	An apostrophe ( ' ) or a quote (") in the value is represented by two
consecutive apostrophes or quotes.



[*] The units depend on the value of the
FORTRANOPT environment variable. If the value is vaxio, then the
record length is in units of 32-bit words. If FORTRANOPT is not defined,
or its value is something other than vaxio, then the record length is
always in units of bytes.

[*]
 For programs run in a DOS environment, newline is considered to be an ASCII
CR-LF (carriage return - line feed) pair. For a non-DOS environment, newline is
considered to be just LF.


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