Chapter 15.1

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Chapter 15.1 Files for input and output
Lets cut down on keyboard input! Can we save
the output?
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Definitions

• File (data file) A collection of data, stored
  under a common name, on a storage medium other
  than main memory
• Examples C programs, Saved messages
• File Stream a one-way transmission path, used
  to connect a file stored on a device (like a
  disk) to a program
• Mode determines the direction of data on the
  transmission path
• Input file stream reads data from a file
• Output file stream writes data to a file

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Input and Output file streams
Program
Disk
include ltfstreamgt int main () ( return 0
Input file stream
file
Output file stream
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File Stream Objects and Methods

• If you want to use a file for output, declare a
  variable of ofstream type
• ofstream output file streams
• ofstream Outfile
• ofstream Out
• If you want to use a file for input, declare a
  variable of ifstream type
• ifstream input file streams
• ifstream Infile
• ifstream In
• Any variable name can be used as long as it
  conforms to Cs identifier rules

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File Stream methods

• Prewritten functions
• Connecting a stream to an external file name
  opening a file
• Infile.open (Student.data, ios in)
• Determining whether a successful connection has
  been made
• if (Infile.fail( ))
• Closing a connection
• Infile.close ( )

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Syntax for Output Files

• include ltofstreamgt
• Declare Outfile as an object of type fstream
• ofstream Outfile
• Open the external file with the statement
• Outfile.open (Report.out,iosout)
• Outfile is name in program, Report.out is
  external filename
• Write to the file
• Outfile ltlt Grade\t ltlt grade
• (writes to the file instead of the screen)
• use Outfile instead of cout (start/debug with
  cout)
• Close the file
• Outfile.close()

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Syntax for Input Files

• include ltifstreamgt
• Declare Infile as an object of type ifstream
• fstream Infile
• Open the external file with the statement
• Infile.open (Student.data,iosin)
• Infile - name in program, Student.data - external
  filename
• Read from the file
• Infile gtgt grade
• (reads from the file instead of from the
  keyboard)
• use Infile instead of cin (Make sure file
  exists!)
• Close the file
• Infile.close()

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Mode Indicators

• ios in
• ios out
• ios app
• ios ate
• ios binary
• ios trunc
• ios nocreate
• ios noreplace

• open in input mode
• open in output mode
• open in append mode
• go to end of opened file
• open in binary mode (default, text)
• Delete file contents, if it exists
• If file does not exist, open fails
• If file exists, open for output fails

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Same file for input and output

• include ltiostreamgt
• include ltfstreamgt
• Using namespace std
• main ()
• fstream file1
• int HW, newgrade
• System(clear)
• / Open the file for input /
• file1.open ("grades.dat", iosin)
• cout ltlt "Homework total is "
• file1 gtgt HW // Print score that was read from
  file
• cout ltlt HW ltlt '\n'
• file1.close () // Close input file

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Keep Value Around Between Runs

• / Add score from keyboard /
• cout ltlt "What is score to be added?"
• cin gtgt newgrade
• cout ltlt '\n'
• HW newgrade
• cout ltlt "Homework total is now "
• cout ltlt HW ltlt '\n'
• / Reopen the file for output /
• file1.open ("grades.dat", iosout)
• file1 ltlt HW
• file1.close()
• return 0
• //Run it again, new score is there!

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Read until End of File (EOF)

• void main (void)
• fstream TestFile
• TestFile.open ("loop.file", iosin)
• int TestScore, ID, Zip
• // Read first record
• TestFile gtgt TestScore gtgt ID gtgt Zip
• while ( TestFile.eof() 0)
• //same as (! TestFile.eof() )
• // Process record
• Cout ltlt TestScore ltlt ID ltlt Zip
• // Read next record
• TestFile gtgt TestScore gtgt ID gtgt Zip
• // end while
• TestFile.close() // end main