chapter 8 foc

• File


  A set of data stored on a computer, often on a disk drive
• File input and output

  • Can use files instead of keyboard and monitor screen for program input and output
  • Allows data to be retained between program runs
  • Programs can read from and/or write to files
  • Used in many applications: word processing, databases, spreadsheets, compilers
• File operations


  1. Open the file

  2. Use the file (read from, write to, or both)

  3. Close the file
• ifstream


  Data type for input files, open for input only and file cannot be written to, open fails if file does not exist

  
• ofstream


  Data type for output files, open for output only and file cannot be read from, file created if no file exists, file contents erased if file exists

  
• fstream


  Data type for both input and output files, must specify mode on the open statement
• fstream open modes


  • ios::in for input mode
  • ios::out for output mode
  • ios::binary for binary mode
  • ios::app for append mode
• Opening files


  1. Create a link between file name (outside the program) and file stream object (inside the program)

  2. Filename may include drive and/or path info

  3. Use the open() member function
• Output file will be created if necessary; existing file will be erased first
• Input file must exist for open to work
• Checking file open errors

  1. File stream object set to 0(false), if open failed

  2. Use fail() member function to detect file open error

  3. Use is_open() member function to check if a file is open
• Using files


  1. Use output file object and << to send data to a file

  2. Use input file object and >> to copy data from file to variables

  3. Use eof() member function to test for end of input file

  
• Closing files


  1. Use the close() member function

  2. Don't wait for operating system to close files at program end