CIS 403503 Accelerated DataFile Structures

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CIS 403/503Accelerated Data-File Structures

• Lecture 8
• C Template Output

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Objectives

• In this lecture, you will learn
• Function Template
• Class Template
• Specialized Template
• I/O Streams
• File Input Output

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Function Template
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Function Template

• A pattern of a possible function
• Generic programming

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Find Max

• int max(int x, int y)
• return (x gt y)?xy
• double max (double x, double y)
• return (x gt y)?xy

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Template

• template ltclass Tgt max (T x, T y)
• return (xgty)?xy
• Note keyword class and typename can be used
  interchangeably

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Class Template
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Class Template

• Similar to function template, a class template
  may work for any type of object
• Just as function template is not a function, a
  class template is not a class

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Example

• ifndef GENERICOBJECT_H
• define GENERICOBJECT_H
• template lttypename Objectgt
• class GenericObject
• public
• explicit GenericObject(const Object
  initValObject())storedValue(initVal)
• const Object getValue() const return
  storedValue
• void setValue(const Object val) storedValue
  val
• private
• Object storedValue
• endif

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Use of GenericObject

• include GenericObject.h
• include ltiostreamgt
• using namespace std
• int main ( )
• GenericObjectltintgt x1
• GenericObjectltdoublegt x2(1)
• x1.setValue(2)
• x2.setVaue(x2.getValue()2)
• cout ltlt x1.getValue() ltlt endl
• cout ltlt x2.getValue() ltlt endl
• return 0

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Specialized Template
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Multiple Template Parameters

• The template parameter list may have more than
  one parameter
• template ltclass Key, class PlainTextgt
• class Cipher
• Cipherltint, stringgt shift

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Template Nontype Parameters

• A non-type parameter must be a compile-time
  constant
• template lttypename Object, int sizegt
• class Buffer
• Buffer ltstring, 1024gt buf

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Default Template Parameters

• Template parameter list can have default values
  for both type and nontype parameters
• template ltclass Objectchar, int size1024gt
• class Buffer
• Bufferltintgt buf1
• Bufferltgt buf2

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I/O Stream
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Four Standard Streams

• cin
• Standard input
• cout
• Standard output
• cerr
• Standard error
• Clog
• Standard log stream

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Error States

• Four states
• End-of-file
• Stream saw end-of-file
• Fail
• Unsuccessful operation
• Bad
• Invalid operation, possibly corrupted stream
• Good
• Non of above

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Example

• template ltclass Objectgt
• void readData(istream in, Object obj)
• string tmp
• while (!(in gtgt obj).eof())
• if (in.fail())
• in.clear() //clear error state
• in gtgt tmp
• cerr ltlt Skipping ltlt tmp ltlt endl

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Output

• Format the output by using manipulators
• cout ltlt setw(15) //set field width
• cout ltlt left //field on left
• cout ltlt right
• cout ltlt setprecision(2)
• cout ltlt scientific // double with sci-notation
• cout ltlt fixed //double no sci-notation

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Input

• Istreams support a get method to get a character
  one at a time
• istream get (char ch)
• e.g.
• char ch
• if (cin.get(ch))
• cout ltlt read ltlt ch ltlt endl
• else
• cout ltltread error ltlt endl

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More Input

• Use unget to undo a get
• Use peek to examine the next character without
  actually read it
• istream unget()
• int peek()
• If end-of-file, return EOF as an integer value

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File Input Output
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Files

• ifstream for input
• ofstream for output
• Opena file stream with primitive strings and
  modes
• String constant
• Null-terminated char array
• c_str on a string object

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Examples

• ifstream f1(test.data)
• char filename1100
• get(filename1, 100) //read a whole line or 99
  chars
• ofstream f2(filename)
• string filename2
• cin gtgtgt filename2
• ofstream f3(filename2.c_str(), iosout
  iostrunc)
• string filename3
• getline(cin, filename3)
• ofstream f4(filename3.c_str(), iosoutiosapp)

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Modes

• iosin
• Open file for reading
• iosout
• Opern file for writing
• iosate
• Initial file end of file
• iosapp
• Appen output
• isotrunc
• Erase exising file before write
• iosbinary
• Write binary file

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Random Access

• ifstream has a pointer known as get pointer that
  points to the next element to be read
• ofstream has a pointer put pointer that points to
  the location where the next element has bo be
  written.
• May re-position the current pointing position

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tellg() and tellp()

• Zero input parameter, return pos_type that is an
  integer data type representing the current
  position of get pointer or put pointer

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seekg() and seekp()

• Change the position of stream pointers
• Both overloaded with two prototypes
• seekg(pos_type position)
• seekp(pos_type position)
• Stream pointers are changed to an absolute
  position from the beginning of the file
• seekg(pos_type position, seekdir direction)
• seekp(pos_type position, seekdir direction)
• Specify an offset determined by direction
• iosbeg
• ioscur
• iosend

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Example

• Void lastChars(const string fileName, int count)
  
• ifstream fin(fileName.c_str(), iosbinary)
• if (!fin)
• //do something
• else if (count lt0)
• cout ltlt invalid counter must gt 0 ltlt endl
• fin.seekg(0, iosend)
• int fileSize fin.tellg()
• if (fileSize lt count)
• count fileSize
• fin.seekg(-count, ioscur)
• char ch
• while (fin.get(ch))
• cout.put(ch)

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Things to Remember

• Template allows generic programming
• Function templates are not functions
• Class templates are not classes
• Templates can be instantiated with multiple
  parameters
• Templates can be instantiated with nontype
  parameters, such as int
• Template parameters can have defaults

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Things to Remember

• Four standard streams are defined cin, cout,
  cerr and clog
• ifstream is a subclass of istream
• ofstream is a subclass of ostream
• iostream extends both istream and ostream
• Error handling is checking the state of the
  stream
• Manipulators are used to control formatting
  options for output
• The istream and ostream allow for random access
  in the stream
• Files are closed automatically by destructors

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Possible Quiz Questions

• How are errors handled in the C I/O library?
• What is wrong with while(!fin.eof())?
• What is a template?
• How to implement and use a function template?
• How to implement and use a class template?