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PGHPF Workstation Reference Manual - 6 Input and Output Formatting

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6 Input and Output Formatting

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 a 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 usd 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. Non-advancing formatted data transfers are a variety of formatted I/O where a portion of a data record is transferred with each input/output statement.
  • list directed input/output is an abbreviated form of formatted input/output that does not use 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.

6.1 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 .[1]RECL can only be used when access is direct.

A record in a variable length formatted file is terminated with \n 2. A record in a variable length unformatted file is preceded and followed by a word indicating the length of the record.

6.1.1 Standard Preconnected Units

Certain input and output units are predefined, depending on the value of compiler options. The pghpf 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.

6.2 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 has the form: 
OPEN (list)
where list contains a unit specifier of the form: 
[UNIT=] u
where u, an integer, is the external unit specifier.

In addition list may contain one of each of the specifiers shown in Table 6-1.

6.2.1 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')

6.2.2 Closing a File

Close a unit by specifying the CLOSE statement from within any program unit. 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 6-1 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.

Table 6-1 OPEN Specifiers

Specifier

Description
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.
ACTION= act
Where act is a character string specifying the allowed actions for the file and is one of READ, WRITE, or READWRITE.
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.
DELIM=del
Specify the delimiter for character constants written by a list-directed or namelist-formatted statement. The options are APOSTROPHE, QUOTE, and NONE.
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.
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.
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.[3
]
PAD=padding
Specifies whether or not to use blank padding for input items. The padding values are YES and NO. The value NO requires that the input record and the input list format specification match.
POSITION=pos
Specifies the position of an opened file. ASIS indicates the file position remains unchanged. REWIND indicates the file is to be rewound, and APPEND indicates the file is to positioned just before an end-of-file record, or at its terminal point.
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.
STATUS= sta
The file status where sta is a character expression: it can be NEW, OLD, SCRATCH, REPLACE 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.
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')

6.3 Data Transfer Statements

Once a unit is connected, either using a preconnection, or by executing an OPEN statement, data transfer statements may be used. The available data transfer statements include: READ, WRITE, and PRINT.

The general form for these data transfer statements is shown in Chapter 3.Refer to Chapter 3 for details on the READ and WRITE and PRINT statements and their valid I/O control specifiers.

6.4 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.

6.5 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.

6.5.1 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

6.5.2 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 6-2:

Table 6-2 Format Character Controls for a Printer

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 I/O 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 )

B Format Control Binary Data

The B field descriptor transfers binary values and can be used with any integer data type. The edit descriptor has the form: 

Bw[.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) binary characters only (0 or 1). 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 B field descriptor transfers the binary valuesof 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.

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 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.

EN Format Control

The EN specifier transfers real values using engineering notation. 

ENw.d   
ENw.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.

On output, the number is in engineering notation where the exponent is divisible by 3 and the absolute value of the significand is 1000 > |significand | >=1. This format is the same as the E format descriptor, except for restrictions on the size of the exponent and the significand.

ES Format Control

The ES specifier transfers real values in scientific notation. The ES format specifier has two basic forms: 

ESw.d   
ESw.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 output the scale factor controls the decimal normalization as in D above.

On output, the number is presented in scientific notation, with the absolute value of the significand is 10> | significand | >= 1.

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

The G format specifier provides generalized editing of real data. The G format 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 format 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.

O Format Control Octal Values

The O and Z field descriptors transfer octal or hexadecimal values and can be used with an integer 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 in an 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

Z Format Control Hexadecimal Values

The O and Z field descriptors transfer octal or hexadecimal values and can be used with any integer 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.

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.

Multiple slashes are permitted, thus multiple records are skipped.

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: 

$

6.6 Non Advancing Input and Output

Nonadvancing input/output is character-oriented and applies to sequential access formatted external files. The file position is after the last character read or written and not automatically advanced to the next record.

For nonadvancing input/output, use the ADVANCE='NO' specifier. Two other specifiers apply to nonadvancing, EOR which applies when end of record is detected and SIZE which returns the number of characters read.

6.7 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

6.7.1 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.

Table 6-3 List Directed Input Values

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 its previous value ( the / terminates the input).

6.7.2 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 6-4.

Table 6-4 Default List Directed Output Formatting

Data Type

Default Formatting 
BYTE


I5


INTEGER*2


I7


INTEGER*4


I12


LOGICAL*1


I5 (L2[4

] 
 )








LOGICAL*2






L2






LOGICAL*4






L2






REAL*4






G15.7e2






REAL*8






G25.16e3






COMPLEX*8






(G15.7e2, G15.7e2)






COMPLEX*16






(G25.16e3, G25.16e3)






CHAR *n






An




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




    

  1. 	New records may begin as necessary.

  2. 	Logical output constants are T for true and F for false. 

  3. 	Complex constants are contained within parentheses with the real and
imaginary parts separated by a comma. 

  4. 	Character constants are not delimited by apostrophes and have each
internal apostrophe (if any are present) represented externally by one
apostrophe 

  5. 	Each output record begins with a blank character to provide carriage
control when the record is printed.

  6. 	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.



6.7.3 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. 


6.8 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.



6.8.1 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:

    

  1. 	The start or end delimiter ($) may be an &.

  2. 	The start delimiter must begin in column 2 of a record.

  3. 	The group-name begins immediately after the start delimiter.

  4. 	The spaces or tabs may not appear within the group-name, within any
item, or within any constants.

  5. 	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.

  6. 	Spaces or tabs may precede the item, the = and the constants.

  7. 	Array items may be subscripted.

  8. 	Character items may be substringed.



6.8.2 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:

    

  1. 	One record is output per value.

  2. 	Multiple values are separated by (, ) .

  3. 	Values are formatted according to the rules of the list-directed write.
Exception: character items are delimited by an apostrophe.

  4. 	An apostrophe ( ' ) or a quote (") in the value is represented by two
consecutive apostrophes or quotes.

 







[1]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.

2On DOS systems a \c\n terminates a record.

[3] If IOSTAT and ERR are not present, the
program terminates if an error occurs.

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



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