Input and OutputInput and OutputInput and OutputInput and Output

Chapter 3Chapter 3Chapter 3Chapter 3

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Chapter TopicsChapter TopicsChapter TopicsChapter Topics I/O Streams, DevicesI/O Streams, Devices Predefined FunctionsPredefined Functions Input FailureInput Failure Formatting OutputFormatting Output Formatting ToolsFormatting Tools File I/OFile I/O

I/O Streams, DevicesI/O Streams, Devices Predefined FunctionsPredefined Functions Input FailureInput Failure Formatting OutputFormatting Output Formatting ToolsFormatting Tools File I/OFile I/O

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I/O Streams, DevicesI/O Streams, DevicesI/O Streams, DevicesI/O Streams, Devices Input streamInput stream

• A sequence of characters/bytesA sequence of characters/bytes• From an input deviceFrom an input device• Into the computerInto the computer

Output streamOutput stream• A sequence of characters/bytesA sequence of characters/bytes• From the computerFrom the computer• To an output deviceTo an output device

Input streamInput stream• A sequence of characters/bytesA sequence of characters/bytes• From an input deviceFrom an input device• Into the computerInto the computer

Output streamOutput stream• A sequence of characters/bytesA sequence of characters/bytes• From the computerFrom the computer• To an output deviceTo an output device

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Input data is considered to be an Input data is considered to be an endless sequence of characters/bytes endless sequence of characters/bytes coming into a program from an input coming into a program from an input device (keyboard, file, etc.)device (keyboard, file, etc.)

Input data is considered to be an Input data is considered to be an endless sequence of characters/bytes endless sequence of characters/bytes coming into a program from an input coming into a program from an input device (keyboard, file, etc.)device (keyboard, file, etc.)

Input StreamsInput StreamsInput StreamsInput Streams

... 1 4 19 34 HI MOM. 7 ..

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cincin and the Extraction Operator >> and the Extraction Operator >>cincin and the Extraction Operator >> and the Extraction Operator >>

A binary operatorA binary operator• Takes two operandsTakes two operands• Name of an input stream on the leftName of an input stream on the left

•cincin for standard input from keyboard for standard input from keyboard• Variable on the rightVariable on the right

Variables can be "cascaded"Variables can be "cascaded" cin >> amount >> count >> direction;cin >> amount >> count >> direction;

Variables should generally be simple typesVariables should generally be simple types

A binary operatorA binary operator• Takes two operandsTakes two operands• Name of an input stream on the leftName of an input stream on the left

•cincin for standard input from keyboard for standard input from keyboard• Variable on the rightVariable on the right

Variables can be "cascaded"Variables can be "cascaded" cin >> amount >> count >> direction;cin >> amount >> count >> direction;

Variables should generally be simple typesVariables should generally be simple types

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The Extraction Operator >>The Extraction Operator >>The Extraction Operator >>The Extraction Operator >> Enables you to do input with the cin Enables you to do input with the cin

commandcommand Think of the >> as pointing to where the Think of the >> as pointing to where the

data will end updata will end up C++ able to handle different types of data C++ able to handle different types of data

and multiple inputs correctlyand multiple inputs correctly

Enables you to do input with the cin Enables you to do input with the cin commandcommand

Think of the >> as pointing to where the Think of the >> as pointing to where the data will end updata will end up

C++ able to handle different types of data C++ able to handle different types of data and multiple inputs correctlyand multiple inputs correctly

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The Reading MarkerThe Reading MarkerThe Reading MarkerThe Reading Marker Keeps track of point in the input stream Keeps track of point in the input stream

where the computer should continue where the computer should continue readingreading

Extraction >> operator leaves reading Extraction >> operator leaves reading marker following last piece of data readmarker following last piece of data read

Keeps track of point in the input stream Keeps track of point in the input stream where the computer should continue where the computer should continue readingreading

Extraction >> operator leaves reading Extraction >> operator leaves reading marker following last piece of data readmarker following last piece of data read

… 1 4 19 34 HI MOM. 7 ..

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The Reading MarkerThe Reading MarkerThe Reading MarkerThe Reading Marker During execution of a cin commandDuring execution of a cin command

• as long as it keeps finding data, it keeps readingas long as it keeps finding data, it keeps reading• when the reading marker hits something when the reading marker hits something notnot data, it data, it quitsquits reading reading

Things in the input stream that cin considers not Things in the input stream that cin considers not datadata• spacesspaces• tab \ttab \t• newline character \n newline character \n

(pressing the RETURN key)(pressing the RETURN key)

• for numeric input, something for numeric input, something nonnonnumericnumeric

During execution of a cin commandDuring execution of a cin command• as long as it keeps finding data, it keeps readingas long as it keeps finding data, it keeps reading• when the reading marker hits something when the reading marker hits something notnot data, it data, it quitsquits reading reading

Things in the input stream that cin considers not Things in the input stream that cin considers not datadata• spacesspaces• tab \ttab \t• newline character \n newline character \n

(pressing the RETURN key)(pressing the RETURN key)

• for numeric input, something for numeric input, something nonnonnumericnumeric

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Input to a Simple VariableInput to a Simple VariableInput to a Simple VariableInput to a Simple Variable charchar

• Skips any white space charactersSkips any white space characters• Reads one characterReads one character• Any other characters in the stream are held Any other characters in the stream are held

for later inputfor later input intint

• Skips white space charactersSkips white space characters• Reads leading + or -Reads leading + or -• Reads numeralsReads numerals• Quits reading when it hits non numeralQuits reading when it hits non numeral

charchar• Skips any white space charactersSkips any white space characters• Reads one characterReads one character• Any other characters in the stream are held Any other characters in the stream are held

for later inputfor later input intint

• Skips white space charactersSkips white space characters• Reads leading + or -Reads leading + or -• Reads numeralsReads numerals• Quits reading when it hits non numeralQuits reading when it hits non numeral

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Input to a Simple VariableInput to a Simple VariableInput to a Simple VariableInput to a Simple Variable double (or float)double (or float)

• Skips leading white spaceSkips leading white space• Reads leading + or –Reads leading + or –• Reads numerals and at most one decimal Reads numerals and at most one decimal

pointpoint• Quits reading when it hits something not Quits reading when it hits something not

numericnumeric

Note example, page 95Note example, page 95

double (or float)double (or float)• Skips leading white spaceSkips leading white space• Reads leading + or –Reads leading + or –• Reads numerals and at most one decimal Reads numerals and at most one decimal

pointpoint• Quits reading when it hits something not Quits reading when it hits something not

numericnumeric

Note example, page 95Note example, page 95

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Predefined FunctionsPredefined FunctionsPredefined FunctionsPredefined Functions Function in a computer language is Function in a computer language is similarsimilar

to concept of a function in mathematicsto concept of a function in mathematics• The function is sent value(s)The function is sent value(s)

• Called "arguments" or Called "arguments" or "parameters""parameters"

• It manipulates the valueIt manipulates the value• It returns a valueIt returns a value

Some functions "do a task"Some functions "do a task"

Function in a computer language is Function in a computer language is similarsimilar to concept of a function in mathematicsto concept of a function in mathematics• The function is sent value(s)The function is sent value(s)

• Called "arguments" or Called "arguments" or "parameters""parameters"

• It manipulates the valueIt manipulates the value• It returns a valueIt returns a value

Some functions "do a task"Some functions "do a task"

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Reading Reading cStringcString Data with Data with cincinReading Reading cStringcString Data with Data with cincin Keyboard response of Keyboard response of twotwo words words

(separated by a space) causes the cin (separated by a space) causes the cin command to quit readingcommand to quit reading• the space is considered the space is considered nonnondata (in spite of data (in spite of

our intent)our intent)

Keyboard response of Keyboard response of twotwo words words (separated by a space) causes the cin (separated by a space) causes the cin command to quit readingcommand to quit reading• the space is considered the space is considered nonnondata (in spite of data (in spite of

our intent)our intent)

???

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Reading Reading cStringcString Data DataReading Reading cStringcString Data Data The The getline ( ) getline ( ) function will allow the function will allow the

programmer to access all the charactersprogrammer to access all the characters The The getline ( ) getline ( ) function will allow the function will allow the

programmer to access all the charactersprogrammer to access all the characters

charchar Array variable Length (max number of characters)

Character which terminates read

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cincin and the and the getget Function Functioncincin and the and the getget Function Function Syntax:Syntax:cin.get(varChar);cin.get(varChar);

ExampleExamplecin.get (chVal);cin.get (chVal);•chValchVal is the parameter is the parameter

• the .the .getget function retrieves a character from function retrieves a character from the keyboardthe keyboard

• stores the character in stores the character in chValchVal

Syntax:Syntax:cin.get(varChar);cin.get(varChar);

ExampleExamplecin.get (chVal);cin.get (chVal);•chValchVal is the parameter is the parameter

• the .the .getget function retrieves a character from function retrieves a character from the keyboardthe keyboard

• stores the character in stores the character in chValchVal

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cincin and the and the ignoreignore Function Functioncincin and the and the ignoreignore Function Function Syntax:Syntax:cin.ignore (intValue, charVal);cin.ignore (intValue, charVal);

Example:Example:cin.ignore (10,'\n')cin.ignore (10,'\n')

The ignore function causes characters in The ignore function causes characters in the input stream to be the input stream to be ignoreignored d (discarded)(discarded)• In this example for 10 characters … or …In this example for 10 characters … or …• Until a newline character occursUntil a newline character occurs• It also discards the newline characterIt also discards the newline character

Syntax:Syntax:cin.ignore (intValue, charVal);cin.ignore (intValue, charVal);

Example:Example:cin.ignore (10,'\n')cin.ignore (10,'\n')

The ignore function causes characters in The ignore function causes characters in the input stream to be the input stream to be ignoreignored d (discarded)(discarded)• In this example for 10 characters … or …In this example for 10 characters … or …• Until a newline character occursUntil a newline character occurs• It also discards the newline characterIt also discards the newline character

The ignore and get also work for other input

streams (such as file input streams)

The ignore and get also work for other input

streams (such as file input streams)

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Using the Using the getline( )getline( )Using the Using the getline( )getline( ) Problem : the getline( ) quits reading when it finds a Problem : the getline( ) quits reading when it finds a

newlinenewline• Suppose you have terminated Suppose you have terminated previous inputprevious input with the with the

<RETURN> key (newline still in input stream)<RETURN> key (newline still in input stream)• getline ( ) finds the newline getline ( ) finds the newline immediatelyimmediately and declares its and declares its

task finishedtask finished• we must somehow discard the newline in the input streamwe must somehow discard the newline in the input stream

Problem : the getline( ) quits reading when it finds a Problem : the getline( ) quits reading when it finds a newlinenewline• Suppose you have terminated Suppose you have terminated previous inputprevious input with the with the

<RETURN> key (newline still in input stream)<RETURN> key (newline still in input stream)• getline ( ) finds the newline getline ( ) finds the newline immediatelyimmediately and declares its and declares its

task finishedtask finished• we must somehow discard the newline in the input streamwe must somehow discard the newline in the input stream

???

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Using the ignore( )Using the ignore( )Using the ignore( )Using the ignore( ) Solution : the ignore( ) commandSolution : the ignore( ) command Tells the program to skip either the next 10 Tells the program to skip either the next 10

characters or until it reaches a newlinecharacters or until it reaches a newline• whichever comes firstwhichever comes first

This effectively discards the newlineThis effectively discards the newline

Solution : the ignore( ) commandSolution : the ignore( ) command Tells the program to skip either the next 10 Tells the program to skip either the next 10

characters or until it reaches a newlinecharacters or until it reaches a newline• whichever comes firstwhichever comes first

This effectively discards the newlineThis effectively discards the newline

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Input FailureInput FailureInput FailureInput Failure Happens when value in the input stream is Happens when value in the input stream is

invalid for the variableinvalid for the variableint x, y;int x, y;cin >> x >> y; // Enter B 37cin >> x >> y; // Enter B 37

Value of 'B' not valid for an intValue of 'B' not valid for an int

View View exampleexample

Happens when value in the input stream is Happens when value in the input stream is invalid for the variableinvalid for the variableint x, y;int x, y;cin >> x >> y; // Enter B 37cin >> x >> y; // Enter B 37

Value of 'B' not valid for an intValue of 'B' not valid for an int

View View exampleexample When an input stream fails When an input stream fails system ignores all further I/Osystem ignores all further I/O

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The The clearclear Function FunctionThe The clearclear Function Function Use the clear to return the input stream to Use the clear to return the input stream to

a working statea working state ExampleExample

look for look for cin.clear()cin.clear()cin.ignore (200,'\n'); cin.ignore (200,'\n'); // to empty out input stream// to empty out input stream

Use the clear to return the input stream to Use the clear to return the input stream to a working statea working state

ExampleExamplelook for look for cin.clear()cin.clear()cin.ignore (200,'\n'); cin.ignore (200,'\n'); // to empty out input stream// to empty out input stream

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Formatting OutputFormatting OutputFormatting OutputFormatting Output Producing proper output in the proper Producing proper output in the proper

format is importantformat is important• Specify decimal precisionSpecify decimal precision• Specify left or right justificationSpecify left or right justification• Align columns of numbersAlign columns of numbers

C++ provides I/O manipulatorsC++ provides I/O manipulators Syntax:Syntax:cout << cout << manipulatormanipulator << expression … << expression …

Producing proper output in the proper Producing proper output in the proper format is importantformat is important• Specify decimal precisionSpecify decimal precision• Specify left or right justificationSpecify left or right justification• Align columns of numbersAlign columns of numbers

C++ provides I/O manipulatorsC++ provides I/O manipulators Syntax:Syntax:cout << cout << manipulatormanipulator << expression … << expression …

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ManipulatorsManipulatorsManipulatorsManipulators Must first of all Must first of all #include <iomanip>#include <iomanip>

For decimal precision useFor decimal precision usecout << setprecision (n) << …cout << setprecision (n) << …

To output floating point numbers in fixed To output floating point numbers in fixed decimal format usedecimal format usecout << fixed << …cout << fixed << …

To force decimal zeros to showTo force decimal zeros to showcout << showpoint << …cout << showpoint << …

Must first of all Must first of all #include <iomanip>#include <iomanip>

For decimal precision useFor decimal precision usecout << setprecision (n) << …cout << setprecision (n) << …

To output floating point numbers in fixed To output floating point numbers in fixed decimal format usedecimal format usecout << fixed << …cout << fixed << …

To force decimal zeros to showTo force decimal zeros to showcout << showpoint << …cout << showpoint << …

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ManipulatorsManipulatorsManipulatorsManipulators To specify right justification in a specified To specify right justification in a specified

number of blanks usenumber of blanks usecout << setw(n) << …cout << setw(n) << …

If the number of blanks required to print If the number of blanks required to print the expression exceeds specified sizethe expression exceeds specified size• Size is ignoredSize is ignored

Problem – print series of names left Problem – print series of names left justified followed by right justified numbersjustified followed by right justified numbersOsgood Smart 1.23Osgood Smart 1.23Joe Schmo 456.78Joe Schmo 456.78

To specify right justification in a specified To specify right justification in a specified number of blanks usenumber of blanks usecout << setw(n) << …cout << setw(n) << …

If the number of blanks required to print If the number of blanks required to print the expression exceeds specified sizethe expression exceeds specified size• Size is ignoredSize is ignored

Problem – print series of names left Problem – print series of names left justified followed by right justified numbersjustified followed by right justified numbersOsgood Smart 1.23Osgood Smart 1.23Joe Schmo 456.78Joe Schmo 456.78

•Names are of different length

•Need variable number of spaces

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ManipulatorsManipulatorsManipulatorsManipulators Print name, then variable number of spaces Print name, then variable number of spaces

using the setw( )using the setw( ) Example Example cout << showpoint << fixed ;cout << showpoint << fixed ;cout << name << cout << name << setw( 25 - strlen(name))<<" "; setw( 25 - strlen(name))<<" ";cout << setw (8) << cout << setw (8) << setprecision(2) << amt; setprecision(2) << amt;

Print name, then variable number of spaces Print name, then variable number of spaces using the setw( )using the setw( )

Example Example cout << showpoint << fixed ;cout << showpoint << fixed ;cout << name << cout << name << setw( 25 - strlen(name))<<" "; setw( 25 - strlen(name))<<" ";cout << setw (8) << cout << setw (8) << setprecision(2) << amt; setprecision(2) << amt;

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Formatting ToolsFormatting ToolsFormatting ToolsFormatting Tools Possible to specify a character to fill Possible to specify a character to fill

leading spacesleading spacescout.fill ('*');cout.fill ('*');cout << setw(10) << cout << setw(10) << setprecision(2); setprecision(2);cout << pmtAmount cout << pmtAmount ;;

ResultResult*****12.34*****12.34

Possible to specify a character to fill Possible to specify a character to fill leading spacesleading spacescout.fill ('*');cout.fill ('*');cout << setw(10) << cout << setw(10) << setprecision(2); setprecision(2);cout << pmtAmount cout << pmtAmount ;;

ResultResult*****12.34*****12.34

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File I/OFile I/OFile I/OFile I/O Previous discussion has considered input Previous discussion has considered input

from the keyboardfrom the keyboard• This works fine for limited inputThis works fine for limited input• Larger amounts of data will require file inputLarger amounts of data will require file input

File:File:An area of secondary storage used to hold An area of secondary storage used to hold informationinformation

Keyboard I/O Keyboard I/O #include <iostream>#include <iostream> File I/O File I/O #include <fstream>#include <fstream>

Previous discussion has considered input Previous discussion has considered input from the keyboardfrom the keyboard• This works fine for limited inputThis works fine for limited input• Larger amounts of data will require file inputLarger amounts of data will require file input

File:File:An area of secondary storage used to hold An area of secondary storage used to hold informationinformation

Keyboard I/O Keyboard I/O #include <iostream>#include <iostream> File I/O File I/O #include <fstream>#include <fstream>

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File I/OFile I/OFile I/OFile I/O Requirements to do file I/ORequirements to do file I/O

1.1. #include <fstream>#include <fstream>

2.2. Declare a file stream variableDeclare a file stream variableifstream or ofstream ifstream or ofstream

3.3. Open the file – use the command Open the file – use the command whateverFile.open("filename.xxx");whateverFile.open("filename.xxx");

4.4. Use the stream variable with Use the stream variable with >>>> or or <<<<

5.5. Close the file Close the file whateverFile.close();whateverFile.close();

Requirements to do file I/ORequirements to do file I/O

1.1. #include <fstream>#include <fstream>

2.2. Declare a file stream variableDeclare a file stream variableifstream or ofstream ifstream or ofstream

3.3. Open the file – use the command Open the file – use the command whateverFile.open("filename.xxx");whateverFile.open("filename.xxx");

4.4. Use the stream variable with Use the stream variable with >>>> or or <<<<

5.5. Close the file Close the file whateverFile.close();whateverFile.close();

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File Open ModesFile Open ModesFile Open ModesFile Open Modes In some situations you must specify one or In some situations you must specify one or

more modes for the filemore modes for the file Syntax:Syntax:

fileVariable.open("filename.xxx", fileOpenMode);fileVariable.open("filename.xxx", fileOpenMode);

In some situations you must specify one or In some situations you must specify one or more modes for the filemore modes for the file

Syntax:Syntax:fileVariable.open("filename.xxx", fileOpenMode);fileVariable.open("filename.xxx", fileOpenMode);

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Using Files in ProgramsUsing Files in ProgramsUsing Files in ProgramsUsing Files in Programs Specify Specify #include#include <fstream><fstream> header fileheader file

Declare instance of Declare instance of file to be usedfile to be used

Prepare for access Prepare for access

with with .open( ).open( ) commandcommand

Use name of file in Use name of file in place of cin or coutplace of cin or cout

Specify Specify #include#include <fstream><fstream> header fileheader file

Declare instance of Declare instance of file to be usedfile to be used

Prepare for access Prepare for access

with with .open( ).open( ) commandcommand

Use name of file in Use name of file in place of cin or coutplace of cin or cout

file name on diskfile name on disk

#include <fstream>