Department of Computer and Information Science, School of Science, IUPUI

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Department of Computer and Information
Science,School of Science, IUPUI
Input/Output Streams
File IO

• Dale Roberts, Lecturer
• Computer Science, IUPUI
• E-mail droberts_at_cs.iupui.edu

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File Streams

• Provides high level support for file operations
  in C
• Consists of three components
• ifstream - allows only input
• ofstream - allows only output
• fstream - allows both input and output

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Files -- fstream class

• Inherits from fstreambase and iostream classes
• fstreambase inherits from ios class
• iostream inherits from istream and ostream
  classes
• ifstream inherits from fstreambase and istream
  classes
• ofstream inherits from fstreambase and ostream
  classes

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Class Hierarchies
ios
fstreambase
istream
ostream
ifstream
ofstream
iostream
fstream
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File Stream Functions

• Contains the following functions
• open() - opens the stream
• close() - closes the stream
• attach() - attaches the stream to file descriptor
• setbuf() - set the stream buffer
• rdbuf() - returns the pointer to stream buffer
• str() - returns a pointer to the buffer array

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File Streams - Syntax

• Syntax
• fstream()
• fstream(const char sFileName, int nMode, int
  nProt 0664)
• fstream(filedesc fdif)

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File Processing Modes

• nMode can be any of the following
• iosin - input processing
• iosout - output processing
• iostrunc - discard the file contents
• iosnocreate - the file must exist in order to
  write
• iosnoreplace - cannot rewrite to an existing
  file
• iosbinay - open the file in binary mode
• iosapp - append the new data to the contents of
  the file
• iosate - open the file for output and move to
  the end
• iosiniosout - both input and output

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File Protection Modes

• nProt can be one of the following
• filbufshcompat - compatibility share mode
• filebufsh_none - no sharing
• filebufsh_read - read sharing
• filebufsh_write - write sharing
• filebufsh_readfilebufsh_write - both read
  and write sharing

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File Streams - Example

• fstream my_file
• fstream myfile(cs265.txt, iosin)
• fstream myfile(cs265.txt, iosout)
• const int nMAX_SIZE 256 char bufnMAX_SIZE
• filedesc fdesc my_file.fd()
• fstream fs(fdesc)

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File Streams - open()

• Opens a file as a stream
• Syntax
• void open(const char sfile, int nMode, int nProt
  0664)
• Usage
• fstream my_file my_file.open(cs265.txt,
  iosout)

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File Streams - close()

• Close the opened file.
• The streams error flag is cleared unless the
  close fails.
• Syntax
• void close()
• Usage
• my_file.close()

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File I/O - Example

• includeltiostream.hgt includeltfstream.hgt
• main() // fIn and fOut are objects of
  class fstream fstream fIn, fOut int
  nCnt 0 //for byte count char cCh
• //Open the file copy.in for reading
  fIn.open("copy.in", iosin)
• //Open the file copy.out for writing
  fOut.open("copy.out", iosout)

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File I/O Example contd

• //Until the end of file is reached, read from
  //the file and write it to the out file and
  echo on the screen. while(fIn.get(cCh))
  fOut.put(cCh) cout.put(cCh) //echo on
  terminal nCnt
• //Write the final byte count cout ltlt "
  " ltlt nCnt ltlt " " ltlt endl fOut ltlt nCnt
• //Close the files fIn.close()
  fOut.close()
• return 0

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File I/O - Files

• copy.in
• abcd efg hi j
• copy.out
• abcd efg hi j 14