Transcript Engineering H192 - Computer Programming I/O Manipulation Lecture 27 Winter Quarter The Ohio State University Gateway Engineering Education Coalition Lect 27 P.

Engineering H192 - Computer Programming
I/O Manipulation
Lecture 27
Winter Quarter
The Ohio State University
Gateway Engineering Education Coalition
Lect 27
P. 1
Engineering H192 - Computer Programming
Stream I/O Library Header Files
Note:
There is no “.h” on standard header files.
Be careful about “using namespace std”
• iostream -- contains basic information required for all
stream I/O operations
• iomanip -- contains information useful for performing
formatted I/O with parameterized stream manipulators
• fstream -- contains information for performing file I/O
operations
• strstream -- contains information for performing inmemory I/O operations (i.e., into or from strings in
memory)
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Engineering H192 - Computer Programming
Classes for Stream I/O in C++
ios is the base class.
istream and ostream inherit from ios
ifstream inherits from istream (and ios)
ofstream inherits from ostream (and ios)
iostream inherits from istream and ostream (& ios)
fstream inherits from ifstream, iostream, and ofstream
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Engineering H192 - Computer Programming
C++ Stream I/O -- Stream Manipulators
• C++ provides various stream manipulators that
perform formatting tasks.
• Stream manipulators are defined in <iomanip>
• These manipulators provide capabilities for
– setting field widths,
– setting precision,
– setting and unsetting format flags,
– flushing streams,
– inserting a "newline" and flushing output stream,
– skipping whitespace in input stream
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Engineering H192 - Computer Programming
C++ Stream I/O -- Stream Manipulators
setprecision ( )
• Select output precision, i.e., number of significant
digits to be printed.
• Example:
cout << setprecision (2) ; // two significant digits
setw ( )
• Specify the field width (Can be used on input or output,
but only applies to next insertion or extraction).
• Example:
cout << setw (4) ;
// field is four positions wide
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Engineering H192 - Computer Programming
C++ Stream I/O -- Stream Format States
• Various ios format flags specify the kinds of
formatting to be performed during stream I/O.
• There are member functions (and/or stream
manipulators) which control flag settings.
• There are various flags for trailing zeros and
decimal points, justification, number base,
floating point representation, and so on.
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Engineering H192 - Computer Programming
Stream I/O Format State Flags
ios::showpoint
when set, show trailing decimal
point and zeros
ios::showpos
when set, show the + sign before
positive numbers
ios::basefield
ios::dec
ios::oct
ios::hex
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use base ten
use base eight
use base sixteen
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Engineering H192 - Computer Programming
Stream I/O Format State Flags
ios::floatfield
ios::fixed
ios::scientific
ios::adjustfield
ios::left
ios::right
ios::internal
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use fixed number of digits
use "scientific" notation
use left justification
use right justification
left justify the sign, but right
justify the value
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Engineering H192 - Computer Programming
Stream I/O Format State Flags
ios::eofbit
set when eof encountered [ stream.eof() ]
ios::failbit
set when format error occurred on the
stream, but no characters were lost
[ stream.fail() or simply ! stream ]
ios::badbit set when stream error occurs that
results in a loss of data [ stream.bad() ]
ios::goodbit set when none of the bits eofbit,
failbit, or badbit are set [ stream.good() ]
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Engineering H192 - Computer Programming
I/O Stream Member Functions
.setf ( )
• Allows the setting of an I/O stream format flag.
• Examples:
// To show the + sign in front of positive numbers
cout.setf (ios::showpos) ;
// To output the number in hexadecimal
cout.setf (ios::hex, ios::basefield) ;
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Engineering H192 - Computer Programming
I/O Stream Member Functions
.precision ( ) ;
• Select output precision, i.e., number of significant
digits to be printed.
• Example:
cout.precision (2) ; // two significant digits
.width ( ) ;
• Specify field width. (Can be used on input or output,
but only applies to next insertion or extraction).
• Example:
cout.width (4) ;
// field is four positions wide
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Engineering H192 - Computer Programming
I/O Stream Member Functions
.eof ( ) ;
• Tests for end-of-file condition.
• Example:
cin.eof ( ) ; // true if eof encountered
.fail ( ) ;
• Tests if a stream operation has failed.
• Example:
cin.fail ( ) ; // true if a format error occurred
! cin;
// same as above; true if format error
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I/O Stream Member Functions
.clear ( ) ;
• Normally used to restore a stream's state to "good" so
that I/O may proceed or resume on that stream.
• Example:
cin.clear ( ) ;
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// allow I/O to resume on a "bad"
// stream, in this case "cin",
// on which error had previously
// occurred
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Engineering H192 - Computer Programming
Using Manipulators & Member Functions
#include <iostream> // No “.h” (standard header)
#include <iomanip> // No “.h” (standard header)
using namespace std; // To avoid “std::”
int main ( )
{
int a, b, c = 8, d = 4 ;
float k ;
char name[30] ;
cout << "Enter your name" << endl ;
cin.getline (name, 30) ;
cout << "Enter two integers and a float " << endl ;
cin >> a >> b >> k ;
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Engineering H192 - Computer Programming
Using Manipulators & Member Functions
// Now, let's output the values that were read in
cout << "\nThank you, " << name << ", you entered"
<< endl << a << ", " << b << ", and " ;
cout.width (4) ;
cout.precision (2) ;
cout << k << endl ;
// Control the field and precision another way
cout <<"\nThank you, " << name << ", you entered"
<< endl << a << ", " << b << ", and " << setw (c)
<< setprecision (d) << k << endl ;
}
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Engineering H192 - Computer Programming
Example Program Output
Enter your name
R. J. Freuler
Enter two integers and a float
12 24 67.85
Thank you, R. J. Freuler, you entered
12, 24, and •
68
Thank you, R. J. Freuler, you entered
12, 24, and •
67.85
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More Input Stream Member Functions
.get ( ) ;
Example:
char ch ;
ch = cin.get ( ) ; // gets one character from keyboard
// & assigns it to the variable "ch"
.get (character) ;
Example:
char ch ;
cin.get (ch) ;
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// gets one character from
// keyboard & assigns to "ch"
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Engineering H192 - Computer Programming
More Input Stream Member Functions
.get (array_name, max_size) ;
Example:
char name[40] ;
cin.get (name, 40) ;
// Gets up to 39 characters
// and inserts a null at the end of the
// string "name". If a delimiter is
// found, the read terminates. The
// delimiter is not stored in the array,
// but it is left in the stream.
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Engineering H192 - Computer Programming
More Input Stream Member Functions
.getline (array_name, max_size) ;
Example:
char name[40] ;
cin.getline (name, 40) ; // Gets up to 39 characters
// and assigns the string to "name". A
// null is inserted at the end of the string.
// Note that if a delimiter is found,
// it is removed from the stream, but it is
// not stored in the character array.
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Engineering H192 - Computer Programming
More Input Stream Member Functions
.ignore ( ) ;
Ex:
cin.ignore ( ) ;
// gets and discards 1 character
cin.ignore (2) ; // gets and discards 2 characters
cin.ignore (80, '\n') ;
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// gets and discards up to 80
// characters or until "newline"
// character, whichever comes
// first
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Engineering H192 - Computer Programming
More Input Stream Member Functions
.peek( ) ;
Ex:
char ch ;
ch = cin.peek ( ) ; // peek at (don't take) character
.putback( ) ;
Ex:
char ch;
cin.putback (ch) ; // put character back in stream
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Engineering H192 - Computer Programming
More I/O Stream Member Functions
.read( ) ; .write( ) ;
Ex:
char gross[144] ;
cin.read(gross,144) ; // reads 144 characters from
// input stream. Does NOT
// append '\0'
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Engineering H192 - Computer Programming
File I/O with C++
#include <fstream>
using namespace std;
int main ( ) {
int a, b, c ;
ifstream fin ;
fin.open ( "my_input.dat") ;
fin >> a >> b ;
c=a+b;
ofstream fout ;
fout.open ( "my_output.dat");
fout << c << endl ;
fin.close ( ) ;
fout.close ( ) ;
}
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//Create file input stream object
//Open input file
//Read two values from input file
//Create file output stream object
//Open output file
//Write result to output file
//Close input file
//Close output file
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