4.1.6.1. Print Statements¶

The print statement is used to send output to monitor - can use single or double quotes.

• The format statement of es22.15 is typical for double precision, which is usually to 15 digits of precision. We have 22 character positions (including dot, exponent and 2 signs), so the largest number that could be printed is (which may depend on what we expect) - but this is nothing to do with machine precision:

most positive = +9.999999999999999E+99
smallest = +9.999999999999999E-99
most negative = -9.999999999999999E+99

• Choosing the format of integers may depend on what we expect - so if the maximum number of iterations is 50, we might choose i2 which would cover this range - again this is nothing to do with machine precision of integers:

largest = 99
smallest = 0

print '(i10, es22.15)', 2, 1.0d10
print "(i10, es22.15)", 2, 1.0d10

print 10, x, iterations
10 format("solver returns x=", es22.15," after", i3, " iterations")

print 11, y, iterations
11 format('solver returns y=', es22.15,' after', i3, ' iterations')

print *, "Velocity v=", v, "m/s"
print *, 'Velocity u=', v, 'm/s'

print *, ""

print "(a)", "x = "
do i = 1, nx, 1
    print "(11g12.4)", x(i, :)
end do

4.1.6.2. Opening, Closing, Reading from and Writing to Files¶

• In Fortran each file is associated with a unit number, an integer between 1 and 99.

• Some unit numbers are reserved (I usually start from 10):

  • 5 is keyboard input

  • 6 is keyboard output

• iostat will be non-zero if there is an error - can be used to detect the type of error

• err then specifies the line number with which to proceed should an error be encountered, perhaps to print to the screen. Error lables can start at 1.

write(10, '(i10, 2e22.15)', iostat=write_error, err=10) n, velocity, pressure

read(10, '(i10, 2e22.15)', iostat=read_error, err=20) n, velocity, pressure

open(10, file='data.txt', iostat=open_error, status='unknown', err=30)

close(10, iostat=close_error, err=40)

4.1.6.3. Format of the File¶

Take the following read statement:

read(10, '(i10, 2e22.15)', iostat=read_error, err=20) n, velocity, pressure

The format of the corresponding file must match with comma separated values, i.e.:

1, 200.0, 350.0

4.1.6.4. Format Statements (print, read, write)¶

The key to format statements:

w

m

d

e

n

c

r

format = "(F10.3, A, ES14.7)"

Iw Iw.m

Bw.m Ow.m Zw.m

Fw.d

Ew.d

Ew.dEe

ESw.d ESw.dEe

ENw.d ENw.dEe

Gw.d

Gw.dEe

Lw

A Aw

nX

Tc TLc TRc

r/

r(...)

:

S SP SS

BN BZ

4.1.6.5. Data-Transfer Specifiers (Read, Write)¶

Important specifiers are in bold, typical example:

write(10, '(i10, e22.15, e15.6)', iostat=write_error, err=10) n, velocity, pressure

read(10, '(i10, e22.15, e15.6)', iostat=read_error, err=20) n, velocity, pressure

iostat=integer_variable

err=label

advance='yes'
advance='no'

end=label

eor=label

rec=integer_variable

size=integer_variable

4.1.6.6. I/O Specifiers¶

open(10, file='data.txt', iostat=open_error, status='unknown', err=30)

file='filename'

iostat=integer_variable

status='old'
status='new'
status='replace'
status='scratch'
status='unknown'

err=label

access='sequential'
access='direct'

form='formatted'
form='unformatted'

recl=integer_variable

blank='null'
blank='zero'

access='sequential'
access='direct'

position='asis'
position='rewind'
position='append'

action='read'
action='write'
action='readwrite'

delim='quote'
delim='apostrophe'
delim='none'

pad='yes'
pad='no'

close(10, iostat=close_error, err=50)

iostat

err

status='keep'
status='delete'

4.1.6.7. Reference List¶

This contains commands I haven’t used, but maybe useful for translation/understanding.

call getarg(2, var)

inquire(unit, spec)

inquire(file=filename, spec)

inquire(iolength=iol) outlist

backspace(unit, spec)

endfile(unit, spec)

rewind(unit, spec)

access

action

blank

delim

direct

exist

form

formatted

iostat

name

named

nextrec

number

opened

pad

position

read

readwrite

recl

sequential

unformatted

write

iolength

iostat

err