Fortran 90 New I/O Features, QUB

The Queen's University of Belfast

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New I/O Features

New I/O features

Topics

Non-advancing I/O
INQUIRE by I/O list
NAMELIST
New edit descriptors
New statement specifiers

Non-advancing I/O

Each READ or WRITE normally involves full records
Non-advancing I/O permits READ or WRITE without advancing position to new record
ADVANCE='NO' specifier:

 WRITE(*, '("Input size?")', ADVANCE='NO')

 READ(*, '(I5)') n

Non-advancing I/O not applicable with list directed I/O

INQUIRE by I/O list

INQUIRE (IOLENGTH=length) output-list

To determine the length of an unformatted output item list
May be used as value of RECL specifier in subsequent OPEN statement
Example:

 INTEGER :: rec_len

 ...

 INQUIRE (IOLENGTH = rec_len) name, title, &

  age, address, tel

 ...

 OPEN (UNIT = 1, FILE = 'test', RECL = rec_len, &

  FORM = 'UNFORMATTED')

 ...

 WRITE(1) name, title, age, address, tel

 ...

NAMELIST

Gather set of variables into group to simplify I/O
General form of NAMELIST statement:

NAMELIST /namelist-group-name/ variable-list

Use namelist-group-name as format instead of io-list on READ and WRITE
Input record has specific format:

&namelist-group-name var2=x, var1=y, var3=z/

Variables optional and order unimportant

Example

 ...

 INTEGER :: size = 2

 CHARACTER (LEN = 4) ::      &

 colour(3) = (/ ' red', 'pink', 'blue' /)  

 NAMELIST /clothes/ size, colour

 WRITE(*, NML = clothes)

 ...

outputs:

&CLOTHES SIZE = 2, COLOUR = redpinkblue/

New edit descriptors

EN - (Engineering) Same as E but exponent divisible by 3, value before decimal point between 1 and 1000
ES - (Scientific) Same as E but value before decimal point is between 1 and 10
B - Binary
O - Octal
Z - Hexadecimal
G - Generalised edit descriptor now applicable for all intrinsic types

Example

To compare the differences among E, EN, ES and G edit descriptors:

PROGRAM e_en_es_g_compare IMPLICIT NONE REAL, DIMENSION(4) :: & x=(/1.234, -0.5, 0.00678, 98765.4/) PRINT '(4E14.3/4EN14.3/4ES14.3/4G14.3)',& x, x, x, x END PROGRAM e_en_es_g_compare

Output:

0.123E+01 -0.500E+00 0.678E-02 0.988E+05 1.234E+00 -500.000E-03 6.780E-03 98.765E+03 1.234E+00 -5.000E-01 6.780E-03 9.877E+04 1.23 -0.500 0.678E-02 0.988E+05

New statement specifiers

INQUIRE

 POSITION  =  'ASIS' 'REWIND' 'APPEND' 

 ACTION =  'READ' 'WRITE' 'READWRITE'

 DELIM =  'APOSTROPHE'  'QUOTE'  'NONE'

 PAD =  'YES' 'NO'

 READWRITE  = )

 READ = ) 'YES' 'NO' `UNKNOWN'

 WRITE = )

OPEN

POSITION, ACTION, DELIM, PAD are same as above
STATUS = 'REPLACE'
READ/WRITE

 NML  =  namelist_name

 ADVANCE  =  'YES'  'NO'

READ

EOR = label SIZE = character_count

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