BIL106E

1
BIL106E

• File Processing
• I/O

2

• INTRODUCTION
• FILES RECORDS
• RECORD TYPES
• FILE CONNETION DISCONNECTION
• FILE POSITONNING STATEMENTS

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Files and Records

• Information that is to be preserved after the
  execution of a program is ended is stored in a
  file.
• A file consists of a sequence of records.
• The records in a file may be accessed in a
  sequential manner or in a random access manner.
• Writing to a sequential file destroys all records
  after the one written.
• A file may consist of formatted records and
  optionally one endfile record, or it may consist
  of unformatted records and optionally one endfile
  record.

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• A formatted record is written by a formatted
  write statement or by some means external F and
  consists of a sequence of characters it is read
  by a formatted read statement.
• An unformatted record is written by an
  unformatted write statement and consists of a
  sequence of values in a processor-dependent form
  it is read by unformatted read statement.
• An endfile is written by an endfile statement.
• endfile (auxlist)
• Auxlist consists of a unit specifier and
  optionally an iostat specifier.

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Formated file example
Title row (record)
Data rows (records)
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Unformated file example
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• INTRODUCTION
• FILES RECORDS
• RECORD TYPES
• FILE CONNETION DISCONNECTION
• FILE POSITONNING STATEMENTS

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File Connection Disconnection

• A file must be connected to a program by an open
  statement before it is first used.
• An open statement must specify the type of access
  allowed to the file and the position at which
  reading or writing will start in a sequential
  file.
• open (open_specifier_list)

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open statement

• open (open_specifier_list)
• Some of the specifiers available for use with
  open
• unitunit_number
• filefile_name
• statusfile_status "old", "new" , "scractch",
  "replace"
• formformat_mode "formatted" or "unformatted"
  actionallowed_actions "read" or "write" or
  "readwrite"
• access access_type "sequential" or "direct"
• positionfile_position "rewind" or "append"
• iostatios
• reclrecord_length

Mandatory specifier
Study the rules at pages 270-275
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Examples

• open(unit9,file"Imagine1",status"old",action"r
  ead",
• position"rewind")
• print ,"Please give the name of the output file"
• read " (a) ",out_file
• open(unit9,fileout_file,status"old",action"wri
  te"
• position"append")
• open(unit9,file"datafile",status"old",action"r
  ead"
• position"rewind")

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Examples

• Open unformated (binary) existing file for
  readingopen (unit 6, file My_Data.bin,
  status old, action read, form
  unformatted)
• Open formated (text) existing file for
  readingopen (unit J, file My_Input.txt,
  status old, action read)
• Open direct access file for readingopen (unit
  31, file X23, status old, action read,
  access direct, recl 720)

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Examples

• open(unit7,status"scratch",form"unformatted",
• action"readwrite", position"rewind")
• open(unit13,file"Problem file",form",status"ol
  d",
• access"readwrite",position"rewind",iostatios)
  
• If(ios / 0) then
• Print ,"Error during opening of Problem_file"
• endif
• !continue processing
• If a file is connected to a unit then it may not
  also be connected to another unit
• If a file is connected to a unit then another
  file may not be connected to the same unit.

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close statement

• A file which has been connected to a program by
  means of an open statement can be disconnected by
  means of a close statement.
• close (close_specifiers_list)
• Possible close specifiers are
• unit
• status "keep" or "scratch"
• iostat

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• INTRODUCTION
• FILES RECORDS
• RECORD TYPES
• FILE CONNETION DISCONNECTION
• FILE POSITONNING STATEMENTS

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File Positioning Statements

• There are often situations in which it is
  required to alter the position in a file without
  reading or writing any records.
• backspace(auxlist) causes the file to be
  positioned just before the preceding record.
• rewind(auxlist) causes the file to be positioned
  just before the first record so that a subsequent
  input statement will start reading or writing the
  file from the beginning.
• auxlist unit and iostat (optional) specifiers

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Example

• ! Read up to end-of-file
• do
• read(unit8,iostatios) dummy
• if (ioslt0) then
• exit
• end do
• !Backspace to before end-of-file record
• backspace (unit8)
• ! Now add new information
• write(unit8,)
• ! Terminate file with an end-of-file ready for
  next time
• endfile (unit8)

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Example1

• program fileprg1
• integer, dimension (10) arr
• integer i
• open(unit 1, file"c\filep1.txt",
  status"new", action"write" )
• do i1,10
• write( unit1, fmt"(i5)" ) i
• end do
• end program fileprg1

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Example2

• program fileprg2
• integer, parameter ARR_SIZE 50
• real, dimension(ARR_SIZE,2) koord
• integer, dimension (ARR_SIZE) temp
• integer sizeInFile
• integer i, isEOF
• character (len30) dizi
• sizeInFile0
• open(unit 1, file"e\filep2.txt",
  status"old", action"read" )
• i0
• read( unit 1, fmt"(a30)" ) dizi
• print "(7x, a30)", dizi
• do
• read( unit 1, fmt"(f5.1,tr1, f5.1,tr1,i2)" ,
  iostatisEOF) koord(i,12), temp(i)
• if(isEOF lt 0) then
• exit
• end if
• print "(i3, 2f8.2,i3)" ,i, koord(i,1),
  koord(i,2), temp(i)
• ii1

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Example3

• fileprg2a.f in Week10-examples.zip

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Homework

• Write a program to access a given input file and
  read formatted data from this file. In given
  formatted input file, first , second and third
  columns indicate the students id number, name
  and scores taken from an exam, respectively.
• Your program should read the formatted data,
  find the highest score and students id and name
  with the highest score and print them to a
  previously opened output file with the same
  format given in the input file.

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Input File

• 10000111 Ali Veli 55
• 40010247 Ahmet Kutsi 60
• 80020214 Sezer Yildirim 75
• 40010257 Ayse Kucuk 65
• 30010148 Gokhan Akyidiz 88
• 87010085 Serhat Batmaz 87
• 88010050 Kerem Rahmi Uzun 65
• 40001050 Mustafa Hakyemez 54
• 10002510 Oguz Undes 74
• 20000250 Sevil Yilmaz 78