File IO

1
File I/O

• Every I/O file has
• A unique identifying number
• A unique file name
• ASCII (or text files) also have
• A newness status (old, unknown, new)
• Binary files have
• Access (either direct or sequential)
• Direct meaning each line can be accessed uniquely
• Sequential meaning lines have to be read in, in
  order
• Form (either formatted or unformatted)
• Formatted - data is represented in external
  character form
• Unformatted - data is represented in internal
  binary form
• Record length (if direct access

2
OPENing files

• To open a file (whether writing to or from)
• ASCII examples
• open(1,filegroupstats.txt,statusold)
• open(14,filefname,statusunknown)
• Rarely use new -- too restrictive
• Filename must be a string - no numbers
• ID number could be a variable
• Binary examples
• open(2,fileaugtemp.bin,accessdirect,
  formunformatted,recl42144)
• Recls 4 at end is machine dependent. Refers to
  size of a byte

3
CLOSE and INQUIRE

• Just need ID number to close
• close(2)
• INQUIRE provides information on a file that was
  opened
• inquire(2,existfileexist)
• Where exist is a keyword, and fileexist is an
  arbitrary variable name of type LOGICAL
• if(fileexist.eq.T) then

4
Free formatting ()

• An asterisk () denotes free format I/O
• read , - read input freely from keyboard that
  is delimited either by white space or commas.
  Character/strings must be enclosed by
  apostraphies (e.g. Beth)
• read(1,) - read in data that is space or comma
  delimited from the file recognized as unit 1.
  Character strings need to be surrounded by
  apostrophes (very rarely does this occur)
• print , or write(,) - prints output freely to
  screen with only default format
• print 20, or write(20,) - writes output to the
  file with the unit ID of 20
• Free formatted files are not lined up in columns

5
Fixed Formatted I/O

• Fixed format means a specified number of columns
  is associated with each variable or space of
  interest
• 123456789 lt-- column
• 1983 Bob6
• 2002 Tim9
• Formats for
• Integers I
• Reals F
• Characters A
• Spaces X

6
More Fixed Formatting

• Example
• 04092003 Sand Harbor -114.532 40.628 12.2
• To read in the following variables from this
  line month, day, year, name, lon, lat, temp
• Format code i2,i2,i4,1x,a11,1x,f8.3,1x,f6.3,f11.
  1
• If the length is 1, can omit for any data type
• Note the length of a real number is lttotal
  columnsgt.ltcolumns after decimalgt
• You do NOT have to list the format for the entire
  line.
• Could have left this lines format as
  i2,i2,i4,1x,a11
• Use X format for skipping anything
• If wanted to ignore the name, could have use the
  following i2, i2, i4,13x,f8.3
• Can use multipliers for constant patterns
• 2i2,i4,13x,f8.3
• a11,6(i3,f4.0)

7
FORMAT statement and ID

• 04092003 Sand Harbor -114.532 40.628 12.2
• integer month, day, year
• real temp(12,31,19992003)
• open(1,filetemp.txt,statusold)
• read(1,1000) month, day, year,
• temp(month,day,year)
• 1000 format(i2,i2,i4,28x,f11.2)
• open(10,filetemp.out,statusunknown)
• write(1,1010) year, month,
  temp(month,9,year)
• 1010 format(i4,i2.2, 09,f6.2)

8
Format shorthand

• If format is short, can include it in the
  read/write statement
• read(13,(i6,f3.2)) idate, rh
• write(1,(6i2)) month, day, year, hour, min, sec
• Read(10,(12f4.2)) (monTemp(I),I1,12)

9
Binary format I/O

• Since unformatted, need to specify record number
  if direct access
• open(1,filetemp.bin,accessdirect,formunfor
  matted,recl124)
• read(1,rec1)(temp(I),I1,12)
• open(1,filemodelgrid.bin,accessdirect,form
  unformattedrecl128644)
• read(1,rec32)((temp(ilon,ilat),ilon1,128),ilat1
  ,64)
• For binary files, need to know
• How many records are there?
• How long is each record
• How is each record written out if more than one
  dimension

10
We Try It!

• Calculate the average amperage of the lightning
  strike data in
• /data2/fortran_class/transfer/lightning.sm.txt

11
We Try It!

• Using /data2/fortran_class/transfer/drd964x.pdsi.t
  xt (monthly pdsi data for a particular climate
  division), find the following
• Worst drought month on average
• Worst drought year and month
• Worst drought year

12
You Try It!

• Using data from /data2/fortran_class/transfer/wx.2
  60203.fwx, answer the following questions
• What is the average August temperature?
• What month has the most precip amount?
• Which year was driest?

13
Characters to numbersand vice versa

• To convert a number to a string
• write(cvar,(i4.4)) ivar
• To convert a string to a number
• read(cvar,(i4.4)) ivar
• Note the structure for both ways is
• XXXX(ltstring-vargt,ltformatgt) ltnum-vargt
• Only difference is whether you write or read

14
Random Number Generator

• Never truly random
• Use seeds of numbers based upon computer clock
• Algorithm based upon the seeds
• UNIX command for date and time
• date ymdHMS
• This number is different every time program runs

15
Code for Random Generator

• We write it together

16
You Try It!

• The Game of Life
• Create a 25x25 grid. Fill the grid with random
  binary values (e.g., 1 or 0, X or ). Each
  square has 8 neighbors with exception to border
  (which is infertile). Run generations with
  following rules
• Birth Organism will be born in each empty
  cell that has exactly 3 neighbors
• Death Organism with 4 neighbors will die
  from overcrowding. Organism with fewer than 2
  will die of loneliness
• Survival An organism with 2 or 3 neighbors
  will survive to next generation

17
Creating file lists and reading from them

• To create a file of a list of files - UNIX
• ls -1 04.fw9 gt calsites.fw9.lst
• The -1 is an argument that means just list a
  filename one line at a time
• The gt means instead of writing the list to the
  default output device (i.e., the monitor/screen),
  write it to the file called calsites.fw9.lst

18
We Try It!

• Compute the average August temperature, relative
  humidity, and wind speed for 8 different
  California weather stations