Sequential Access Files

1
Sequential Access Files

• ITE 285

2
Sequential Access Files

• Also known as __________ or __________
• Data is stored as a __________
• Efficient use of storage
• Can be read / created with __________
• Can be typed to the screen
• 2 Special Characters
• __________
• __________

3
Sequential Access Files

• Also known as text files or ASCII files
• Data is stored as a __________
• Efficient use of storage
• Can be read / created with __________
• Can be typed to the screen
• 2 Special Characters
• __________
• __________

4
Sequential Access Files

• Also known as text files or ASCII files
• Data is stored as a sequence of characters
• Efficient use of storage
• Can be read / created with __________
• Can be typed to the screen
• 2 Special Characters
• __________
• __________

5
Sequential Access Files

• Also known as text files or ASCII files
• Data is stored as a sequence of characters
• Efficient use of storage
• Can be read / created with text editors
• Can be typed to the screen
• 2 Special Characters
• __________
• __________

6
Sequential Access Files

• Also known as text files or ASCII files
• Data is stored as a sequence of characters
• Efficient use of storage
• Can be read / created with text editors
• Can be typed to the screen
• 2 Special Characters
• Carriage Return
• Line Feed

7
Additional Requirements

• __________
• Strings need to be delimited (enclosed) in
  quotation marks
• Will work without except special cases (including
  commas in text)
• __________
• Separate data elements (fields) with commas

8
Additional Requirements

• String Delimiters
• Strings need to be delimited (enclosed) in
  quotation marks
• Will work without except special cases (including
  commas in text)
• __________
• Separate data elements (fields) with commas

9
Additional Requirements

• String Delimiters
• Strings need to be delimited (enclosed) in
  quotation marks
• Will work without except special cases (including
  commas in text)
• Comma Separators
• Separate data elements (fields) with commas

10
Data Storage

• Data is stored as a continuous stream of
  characters
• Data access always from __________
• Read through to __________
• Data cannot be __________ into the middle of file
• Data cannot be __________
• Like a cassette tape

11
Data Storage

• Data is stored as a continuous stream of
  characters
• Data access always from beginning of the file
• Read through to __________
• Data cannot be __________ into the middle of file
• Data cannot be __________
• Like a cassette tape

12
Data Storage

• Data is stored as a continuous stream of
  characters
• Data access always from beginning of the file
• Read through to end of the file
• Data cannot be __________ into the middle of file
• Data cannot be __________
• Like a cassette tape

13
Data Storage

• Data is stored as a continuous stream of
  characters
• Data access always from beginning of the file
• Read through to end of the file
• Data cannot be inserted into the middle of file
• Data cannot be __________
• Like a cassette tape

14
Data Storage

• Data is stored as a continuous stream of
  characters
• Data access always from beginning of the file
• Read through to end of the file
• Data cannot be inserted into the middle of file
• Data cannot be edited
• Like a cassette tape

15
Data in File

• Can be the __________ on every line
• Same number of data elements
• Same data type
• Same order
• Example
• Al Anderson,10.00,45 notice NO spaces
• Betty Baker,11.50,40
• Cathy Carter,9.50,20

16
Data in File

• Can be the same on every line
• Same number of data elements
• Same data type
• Same order
• Example
• Al Anderson,10.00,45 notice NO spaces
• Betty Baker,11.50,40
• Cathy Carter,9.50,20

17
Data in File

• Each line can also contain totally different data
• Example
• 3200 Main Street
• Apt. B
• Mobile,Al,36695

18
Operations with Sequential Files

• __________(Modes Input, Output, Append)
• __________ from the File
• __________ to the File (also Append)
• __________ the File
• __________ Files
• __________ (Data?, Files)
• __________
• __________
• __________
• __________

19
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• __________ from the File
• __________ to the File (also Append)
• __________ the File
• __________ Files
• __________ (Data?, Files)
• __________
• __________
• __________
• __________

20
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• __________ to the File (also Append)
• __________ the File
• __________ Files
• __________ (Data?, Files)
• __________
• __________
• __________
• __________

21
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• __________ the File
• __________ Files
• __________ (Data?, Files)
• __________
• __________
• __________
• __________

22
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• Close the File
• __________ Files
• __________ (Data?, Files)
• __________
• __________
• __________
• __________

23
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• Close the File
• Rename Files
• __________ (Data?, Files)
• __________
• __________
• __________
• __________

24
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• Close the File
• Rename Files
• Deleting (Data?, Files)
• __________
• __________
• __________
• __________

25
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• Close the File
• Rename Files
• Deleting (Data?, Files)
• Error Checking
• __________
• __________
• __________

26
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• Close the File
• Rename Files
• Deleting (Data?, Files)
• Error Checking
• Searching
• __________
• __________

27
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• Close the File
• Rename Files
• Deleting (Data?, Files)
• Error Checking
• Searching
• Sorting???
• __________

28
Operations with Sequential Files

• Open File (Modes Input, Output, Append)
• Read Data from the File
• Write Data to the File (also Append)
• Close the File
• Rename Files
• Deleting (Data?, Files)
• Error Checking
• Searching
• Sorting???
• Merging???

29
File Processing

• 3 Main Steps
• __________
• __________
• __________
• System.IO file libraries
• We must import System.IO to include file
  processing
• Imports System.IO ? In General Declarations

30
File Processing

• 3 Main Steps
• Open the File
• __________
• __________
• System.IO file libraries
• We must import System.IO to include file
  processing
• Imports System.IO ? In General Declarations

31
File Processing

• 3 Main Steps
• Open the File
• Read from / Write To the File
• __________
• System.IO file libraries
• We must import System.IO to include file
  processing
• Imports System.IO ? In General Declarations

32
File Processing

• 3 Main Steps
• Open the File
• Read from / Write To the File
• Close the File
• System.IO file libraries
• We must import System.IO to include file
  processing
• Imports System.IO ? In General Declarations

33
Opening a Sequential File

• FileOpen (FileNumber, FileName, Mode)
• __________ Reference number between 1 511
• Each file has its own unique file number
• __________ The name of the file
• Must include path name if not in the default
  directory (bin\debug)
• __________
• OpenMode.Input
• OpenMode.Output
• OpenMode.Append
• Can only be open in one mode at a time

34
Opening a Sequential File

• FileOpen (FileNumber, FileName, Mode)
• FileNumber Reference number between 1 511
• Each file has its own unique file number
• __________ The name of the file
• Must include path name if not in the default
  directory (bin\debug)
• __________
• OpenMode.Input
• OpenMode.Output
• OpenMode.Append
• Can only be open in one mode at a time

35
Opening a Sequential File

• FileOpen (FileNumber, FileName, Mode)
• FileNumber Reference number between 1 511
• Each file has its own unique file number
• FileName The name of the file
• Must include path name if not in the default
  directory (bin\debug)
• __________
• OpenMode.Input
• OpenMode.Output
• OpenMode.Append
• Can only be open in one mode at a time

36
Opening a Sequential File

• FileOpen (FileNumber, FileName, Mode)
• FileNumber Reference number between 1 511
• Each file has its own unique file number
• FileName The name of the file
• Must include path name if not in the default
  directory (bin\debug)
• Mode
• OpenMode.Input
• OpenMode.Output
• OpenMode.Append
• Can only be open in one mode at a time

37
OpenMode.Input

• Read data from the file __________
• File.Exists (filename) function
• File Not Found runtime error
• Function to determine if the file exists
• Returns boolean
• If file.exists(a\myfile) then
• open the file
• FileOpen(1, a\myfile, OpenMode.Input)
• Else
• MessageBox.Show (Invalid File)
• End If

38
OpenMode.Input

• Read data from the file into the program
• File.Exists (filename) function
• File Not Found runtime error
• Function to determine if the file exists
• Returns boolean
• If file.exists(a\myfile) then
• open the file
• FileOpen(1, a\myfile, OpenMode.Input)
• Else
• MessageBox.Show (Invalid File)
• End If

39
OpenFile.Output

• Write data __________ to the file
• Write data at the __________ of the file
• Existing data will be overwritten
• If file does not exist, it will create it

40
OpenFile.Output

• Write data from the program to the file
• Write data at the __________ of the file
• Existing data will be overwritten
• If file does not exist, it will create it

41
OpenFile.Output

• Write data from the program to the file
• Write data at the BEGINNING of the file
• Existing data will be overwritten
• If file does not exist, it will create it

42
OpenFile.Append

• Write data __________ to the file
• Will write to the __________ of an existing file
• If the file does not exist, it will create it

43
OpenFile.Append

• Write data from the program to the file
• Will write to the __________ of an existing file
• If the file does not exist, it will create it

44
OpenFile.Append

• Write data from the program to the file
• Will write to the END of an existing file
• If the file does not exist, it will create it

45
Read Data from the File

• File must be open for __________
• Read __________ Input(fileNumber, Variable)
• Variable must be of the same data type as the
  data in the file
• Each data item must be read in (starting at
  beginning)
• Can use EOF functions
• Determine End of File
• While NOT EOF (fileNumber)
• process file
• End While

46
Read Data from the File

• File must be open for INPUT
• Read __________ Input(fileNumber, Variable)
• Variable must be of the same data type as the
  data in the file
• Each data item must be read in (starting at
  beginning)
• Can use EOF functions
• Determine End of File
• While NOT EOF (fileNumber)
• process file
• End While

47
Read Data from the File

• File must be open for INPUT
• Read One Item from the File Input(fileNumber,
  Variable)
• Variable must be of the same data type as the
  data in the file
• Each data item must be read in (starting at
  beginning)
• Can use EOF functions
• Determine End of File
• While NOT EOF (fileNumber)
• process file
• End While

48
Read in Entire File

• InputString (fileNumber, amountToReadIn)
• Will read in a __________
• LOF Length of File
• InputString (fileNumber, LOF(fileNumber))

49
Read in Entire File

• InputString (fileNumber, amountToReadIn)
• Will read in a sequence of characters
• LOF Length of File
• InputString (fileNumber, LOF(fileNumber))

50
Write Data to the File

• File must be Open for __________ or __________
• __________
• Write (fileNumber, data)
• can use variable, data, multiple data items,
  etc.
• __________
• Print (fileNumber, data)
• works like the write
• __________
• WriteLine (fileNumber, data)
• works like the write, but insers carriage
  return line feed

51
Write Data to the File

• File must be Open for Output or Append
• __________
• Write (fileNumber, data)
• can use variable, data, multiple data items,
  etc.
• __________
• Print (fileNumber, data)
• works like the write
• __________
• WriteLine (fileNumber, data)
• works like the write, but insers carriage
  return line feed

52
Write Data to the File

• File must be Open for Output or Append
• Write procedure
• Write (fileNumber, data)
• can use variable, data, multiple data items,
  etc.
• __________
• Print (fileNumber, data)
• works like the write
• __________
• WriteLine (fileNumber, data)
• works like the write, but insers carriage
  return line feed

53
Write Data to the File

• File must be Open for Output or Append
• Write procedure
• Write (fileNumber, data)
• can use variable, data, multiple data items,
  etc.
• Print procedure
• Print (fileNumber, data)
• works like the write
• __________
• WriteLine (fileNumber, data)
• works like the write, but insers carriage
  return line feed

54
Write Data to the File

• File must be Open for Output or Append
• Write procedure
• Write (fileNumber, data)
• can use variable, data, multiple data items,
  etc.
• Print procedure
• Print (fileNumber, data)
• works like the write
• WriteLine procedure
• WriteLine (fileNumber, data)
• works like the write, but insers carriage
  return line feed

55
Close the File

• FileClose (fileNumber)
• Breaks __________ link with the file
• Disassociated the __________ from the physical
  file
• After closing file
• You may reopen the file in another mode
• Can reuse file number
• You must close the file after all data has been
  read or written

56
Close the File

• FileClose (fileNumber)
• Breaks communication link with the file
• Disassociated the __________ from the physical
  file
• After closing file
• You may reopen the file in another mode
• Can reuse file number
• You must close the file after all data has been
  read or written

57
Close the File

• FileClose (fileNumber)
• Breaks communication link with the file
• Disassociated the file number from the physical
  file
• After closing file
• You may reopen the file in another mode
• Can reuse file number
• You must close the file after all data has been
  read or written

58
Sequential File Homework

• Sequential File Homework
• Payroll Text Files

59
Renaming Files

• Rename (oldFileName, newFileName)
• Must include path if not in Bin\Debug directory

60
Deleting

• Files
• Kill (filename)
• Data
• __________
• Open Current File
• Read data from current file
• If it is the data to be deleted, do nothing
• Else, write it to a second, temporary file
• Loop through steps 2 - 4 until End of current
  file
• Close both files
• Delete first file
• Rename second temporary file with name of first
  file

61
Deleting

• Files
• Kill (filename)
• Data
• Can this be done???
• Open Current File
• Read data from current file
• If it is the data to be deleted, do nothing
• Else, write it to a second, temporary file
• Loop through steps 2 - 4 until End of current
  file
• Close both files
• Delete first file
• Rename second temporary file with name of first
  file

62
Searching

• Read in Data Element
• If it is the data you are searching for, you are
  finished
• Else, read next data element
• If you reach the end of file
• Data does not exist

63
Sorting

• Can this be done???
• Not Really
• Read each data item into an array (or parallel
  arrays)
• Sort the array(s)
• Write the array out to a second temporary file
• Close both file
• Delete first file
• Rename second file with name of first file

64
Merging

• Can this be done???
• Not Really
• Read both files into an array (or parallel
  arrays)
• Sort the array(s)
• Write the array to a new second, temporary file
• Close both files
• Delete first file
• Rename second file with name of first

65
Error Checking

• Trapping actions that can cause an application to
  fail
• __________
• Exceptions that are not handled by code within
  the application
• Divide by Zero
• __________
• Invalid Drive Letter
• File does not exist
• Read/Write from a drive that is empty
• Write to a full drive
• Etc.

66
Error Checking

• Trapping actions that can cause an application to
  fail
• Run-Time errors
• Exceptions that are not handled by code within
  the application
• Divide by Zero
• __________
• Invalid Drive Letter
• File does not exist
• Read/Write from a drive that is empty
• Write to a full drive
• Etc.

67
Error Checking

• Trapping actions that can cause an application to
  fail
• Run-Time errors
• Exceptions that are not handled by code within
  the application
• Divide by Zero
• Files
• Invalid Drive Letter
• File does not exist
• Read/Write from a drive that is empty
• Write to a full drive
• Etc.

68
Structured Exception Handling

• Allows program to catch and deal with run time
  exceptions
• Detect and respond to errors that can occur in a
  running program
• __________
• Try statement
• Write all code that __________
• Code is protected from crashing program
• Catch statement
• Write code to deal with problem, display error
  message
• Will only execute __________ in Try block

69
Structured Exception Handling

• Allows program to catch and deal with run time
  exceptions
• Detect and respond to errors that can occur in a
  running program
• Try Catch statements
• Try statement
• Write all code that __________
• Code is protected from crashing program
• Catch statement
• Write code to deal with problem, display error
  message
• Will only execute __________ in Try block

70
Structured Exception Handling

• Allows program to catch and deal with run time
  exceptions
• Detect and respond to errors that can occur in a
  running program
• Try Catch statements
• Try statement
• Write all code that might cause a problem
• Code is protected from crashing program
• Catch statement
• Write code to deal with problem, display error
  message
• Will only execute __________ in Try block

71
Structured Exception Handling

• Allows program to catch and deal with run time
  exceptions
• Detect and respond to errors that can occur in a
  running program
• Try Catch statements
• Try statement
• Write all code that might cause a problem
• Code is protected from crashing program
• Catch statement
• Write code to deal with problem, display error
  message
• Will only execute if a problem occurs in Try block

72
Catch exceptions

• Catch exceptionVar as ExceptionType
• exceptionVar is the variable name for the
  exception
• ExceptionType is the specific type of exception
• System.IO.File exception types
• SecurityException
• ArgumentException
• ArguementNullException
• PathTooLongException
• DirectoryNotFoundException
• FileNotFoundException
• NotSupportedException

73
Finally Clause

• Code that will execute __________ the Try
  statements (and any necessary catch statements)
• Code to close file should go here
• Executes __________ an exception occurs or not

74
Finally Clause

• Code that will execute after the Try statements
  (and any necessary catch statements)
• Code to close file should go here
• Executes __________ an exception occurs or not

75
Finally Clause

• Code that will execute after the Try statements
  (and any necessary catch statements)
• Code to close file should go here
• Executes whether an exception occurs or not

76
Example (generic exception)

• Private sub btnFileOpen_Click ()
• Try
• FileOpen(1, myFile.txt, OpenMode.Input)
• txtFile.text InputString (1, LOF(1))
• Catch Err as System.IO.Exception
• MessageBox.show (The file does not exist on
• current drive)
• Finally
• FileClose(1)
• End Try
• End Sub

77
Example (specific exception)

• Private sub btnFileOpen_Click ()
• Try
• FileOpen(1, myFile.txt, OpenMode.Input)
• txtFile.text InputString (1, LOF(1))
• Catch Err as FileNotFoundException
• MessageBox.show (The file does not exist)
• Catch Err as DirectoryNotFoundException
• MessageBox.show (This directory cannot be
  found)
• Catch Err as Exception default, catches all
  other problems
• MessageBox.show (File Error)
• Finally
• FileClose(1)
• End Try
• End Sub

78
File Dialog Boxes

• __________ Windows that appear on screen
• Obtain information from user
• __________
• OpenFileDialog
• Open files for reading
• SaveFileDialog
• Open files for writing

79
File Dialog Boxes

• Dialog Boxes Windows that appear on screen
• Obtain information from user
• __________
• OpenFileDialog
• Open files for reading
• SaveFileDialog
• Open files for writing

80
File Dialog Boxes

• Dialog Boxes Windows that appear on screen
• Obtain information from user
• File Dialog Boxes -
• OpenFileDialog
• Open files for reading
• SaveFileDialog
• Open files for writing

81
File Dialog Boxes

• Add dialog box from the toolbox to the project
• Will appear in the component tray (not on form)
• Name the control (ofd or sfd prefix)
• Display Function ? ControlName.showDialog( )
• Function with return
• - DialogResult.OK file name selected
• - DialogResult.Cancel no file selected

82
Example

• If ofdOpenFile.ShowDialog( ) DialogResult.OK
  then
• FileOpen(1, ofdOpenFile.FileName,
  OpenMode.Input)
• Else
• MsgBox.show (No File was selected)
• End If
• If sfdSaveFile.ShowDialog( ) DialogResult.OK
  then
• FileOpen(2, sfdSaveFile.FileName,
  OpenMode.Append)
• Else
• MsgBox.show (No File was selected)
• End of

83
Dialog Boxes Properties

• __________ (Description, Actual Filter Used)
• Text File (.txt) .txt
• filter only text files
• B) Text Files (.txt) .txt All Files
  (.) .
• Text files and all file extenstion
• __________ Which directory to look in first
• __________ Title Bar of dialog Box

84
Dialog Boxes Properties

• Filter Properties (Description, Actual Filter
  Used)
• Text File (.txt) .txt
• filter only text files
• B) Text Files (.txt) .txt All Files
  (.) .
• Text files and all file extenstion
• __________ Which directory to look in first
• __________ Title Bar of dialog Box

85
Dialog Boxes Properties

• Filter Properties (Description, Actual Filter
  Used)
• Text File (.txt) .txt
• filter only text files
• B) Text Files (.txt) .txt All Files
  (.) .
• Text files and all file extenstion
• Initial Directory Property Which directory to
  look in first
• __________ Title Bar of dialog Box

86
Dialog Boxes Properties

• Filter Properties (Description, Actual Filter
  Used)
• Text File (.txt) .txt
• filter only text files
• B) Text Files (.txt) .txt All Files
  (.) .
• Text files and all file extenstion
• Initial Directory Property Which directory to
  look in first
• Title Property Title Bar of dialog Box