Parallel Computer Centre
Non-advancing I/O obviates the need for records to be read as a whole and for the record length to be known beforehand. It is specified with
ADVANCE='NO'
on the READ or WRITE statement and inhibits the automatic advance to the next record on completion of the statement. If
ADVANCE='YES'
is specified, or the specifier is absent, then the default normal (advancing) I/O occurs.
It is possible to specify advancing and non-advancing I/O on the same record or file. A common use of this is to write a prompt to the screen, specifying non-advancing I/O, and then read the next character position on the screen. For example:
WRITE(*, '("Input size?")', ADVANCE='NO')
READ(*, '(I5)') n
It is often useful to determine how many characters have been read on a non-advancing input. This can be achieved using the SIZE specifier, which has the general form
SIZE=character_count
The integer variable character_count is assigned the number of characters read, excluding any padding characters, on completion of the non-advancing read.
If a non-advancing input reads beyond the end of a record, this can be detected using the IOSTAT specifier which has the form
IOSTAT=io_status
On completion of a READ statement io_status is assigned a value which indicates whether an end-of-record or end-of-file condition has occurred. For example, the NAG compiler returns -1 in the IOSTAT specifier when end-of-file is encountered, and -2 for end-of-record.
INQUIRE(IOLENGTH=length) output-list
The length may be used as a value of the RECL specifier in subsequent OPEN statements. For example,
INTEGER :: rec_len
...
INQUIRE(IOLEMGTH=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 is a facility whereby a set of variables can be gathered together into a named group in order to simplify I/O. The NAMELIST statement is a specification statement and must, therefore, appear before any executable code in the defining program unit. The general form of the NAMELIST statement is:
NAMELIST/namelist-group-name/variable-list
Note that a variable in a NAMELIST group may not be an array dummy argument with non-constant bounds, a variable with assumed character length, an automatic object, an allocatable array, a pointer, or a variable which at any depth of component selection is a pointer.
In READ or WRITE statements, the namelist-group-name may be specified with the NML specifier, or may replace the format specifier. There is no need for input/output lists.
An input record for a namelist group has a specific format:
&namelist-group-name var1=x, var2=y, var3=z
It is possible to omit items when inputting data, and such items remain unchanged. Also, items do not have to be input in the order specified in the NAMELIST statement.
INTEGER :: size=2
CHARACTER (LEN=4) :: colour(3) = (/ ' red','pink','blue' /)
NAMELIST /clothes/ size, colour
WRITE(*, NML = clothes)
The output would be:
&CLOTHES SIZE = 2, COLOUR = redpinkblue/
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
The output would be
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
INQUIRE
OPEN
The specifiers POSITION, ACTION, DELIM and PAD have the same values and meanings as for INQUIRE. One additional value has been provided for the STATUS specifier:
READ/WRITE
READ
Look at the programs non_adv.f90, inquire.f90, namelist.f90, edit1.f90, edit2.f90, and io_spec.f90, and run them.
Notice how these programs use new I/O facilities.