Post on 17-Jan-2016
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Today’s ObjectivesToday’s Objectives
Announcements• Turn in Homework 4• Quiz 4 will be on Wednesday, July 19 – It will have questions about
inheritance, polymorphism, templates, and stream I/O• Homework 5 is due on next Monday, July 24. Since this date is so close to
the end of the semester, no late assignments will be accepted and email will NOT be accepted!
Stream Input/Output (Ch. 15)• Streams• I/O in C++ with streams• Stream error states• Stream manipulators
Bonus Lab 8 – Debugging with MS Visual Studio
17-Jul-200617-Jul-2006
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Stream Input/OutputStream Input/Output
Chapter 15
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StreamsStreams
Stream = a sequence of bytes• Just like a water-filled stream, a C++ stream has a flow,
it can be directed, and it can be stopped. But it cannot flow backwards.
In C++, I/O is accomplished by using streams• A C++ stream is an object – it’s instantiated from a
class, just like any other object• Output – the bytes flow from memory to an output
device• Input – the bytes flow from an input device to memory
Stream I/O (Deitel, 771; Josuttis, 584)Stream I/O (Deitel, 771; Josuttis, 584)
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I/O in C++I/O in C++
Low-level I/O is unformatted I/O• Specifies the number of bytes to transfer• Example: member functions such as “get”, “put”,
“read”, and “write”
High-level I/O is formatted I/O• Uses bytes in groups corresponding to built-in data
types• Example:int n;cin >> n;
wchar_t = a C++ data type used to store Unicode characters
Stream I/O (Deitel, 771–772)Stream I/O (Deitel, 771–772)
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Header FilesHeader Files
<iostream>• Basic stream I/O services• Defines objects: cout, cin, cerr, and clog
<iomanip>• Services for formatted I/O with stream
manipulators
<fstream>• Services for file I/O
Stream I/O (Deitel, 772)Stream I/O (Deitel, 772)
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Stream I/O ClassesStream I/O Classes
Different classes are used to create stream objects for each type of I/O, Fig. 15.1, page 773
istream• Defines input streams• Instantiation of the template class basic_istream<>
using char as the type parameter
ostream• Defines output streams• Instantiation of the template class basic_ostream<>
using char as the type parameter
Stream I/O (Deitel, 772–773; Josuttis, 585)Stream I/O (Deitel, 772–773; Josuttis, 585)
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Global Stream ObjectsGlobal Stream Objects
cin• Predefined object of the istream class• Used for standard user input, normally connected to the keyboard
cout• Predefined object of the ostream class• Used for standard user output, normally connected to the monitor
cerr• Predefined object of the ostream class• Used for error messages, not buffered, normally connected to the monitor
clog• Predefined object of the ostream class• Used for logging messages, buffered, normally connected to the same
device as cerr
Stream I/O (Deitel, 772–773; Josuttis, 585)Stream I/O (Deitel, 772–773; Josuttis, 585)
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Stream OutputStream Output
operator<<• Stream insertion operator• Overloaded for output to ostream objects• It’s typesafe because it’s overloaded for all the built-in
data types, and it can be overloaded for our own classes
Member function put• Member function of the ostream class• Used to output single chars• Examples
cout.put( 'A' );cout.put( 65 ); //Using the ASCII value
Stream I/O (Deitel, 775–776; Josuttis, 586)Stream I/O (Deitel, 775–776; Josuttis, 586)
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Stream InputStream Input
operator>>• Stream extraction operator• Overloaded for input from istream objects• It’s typesafe because it’s overloaded for all the built-in
data types, and it can be overloaded for our own classes
• Ignores whitespace and leaves it in the stream
Member functions of the istream classget, getlineignoreeof, gcountputback, peek
Stream I/O (Deitel, 776–780; Josuttis, 586)Stream I/O (Deitel, 776–780; Josuttis, 586)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
buffer
\nHe l l o
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
buffer H
el l o\n
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
buffer H
ll o \n
e
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
buffer H
lo\n
e l
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
buffer H
o\n
e l l
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
buffer H
\n
e l l o
Leaves the delimiter in the stream
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using get()Using get()
Used with no arguments, it inputs one charchar c = cin.get();
Can be used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.get(buffer,1024,'\n');
buffer
cin
H
\n
e l l o \0Inserts ‘\0’ terminator
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
buffer
\nHe l l o
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
buffer H
el l o\n
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
buffer H
ll o \n
e
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
buffer H
lo\n
e l
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
buffer H
o\n
e l l
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
buffer H
\n
e l l o
Discards the delimiter in the stream
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using getline()Using getline()
Used with three arguments1. char array2. size limit3. delimiter char (optional: default is ‘\n’)
char buffer[1024];cin.getline(buffer,1024);
buffer H e l l o \0Inserts ‘\0’ terminator
cin
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Using read() and write()Using read() and write()
Input• Member function read of the istream class• Inputs bytes into a char array
Output• Member function write of the ostream class• Outputs bytes in a char array
Examplechar buffer[1024];cin.read( buffer, 5 );cout.write( buffer, 5 );
Stream I/O (Deitel, 776–780)Stream I/O (Deitel, 776–780)
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Stream Error StatesStream Error States
A data member of the stream objects identifies whether I/O was successful with the following values
goodbit = everything okay, normally set to 0
eofbit = end-of-file encountered
failbit = operation not successful, but the stream is okay, e.g. char in the stream instead of an integer
badbit = operation not successful, because stream is corrupted or lost, e.g. reading past the end of a file
Stream I/O (Deitel, 766–768; Josuttis 597)Stream I/O (Deitel, 766–768; Josuttis 597)
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Determining the Stream StateDetermining the Stream State
Use the following member functions to determine the state of the flags
good() = returns true if the stream is okay
eof() = returns true if the end-of-file was encountered
fail() = returns true if there was an I/O error
operator! = same as fail()
bad() = returns true if there was a fatal error
clear() = clears all flags
Stream I/O (Deitel, 797–799; Josuttis 597)Stream I/O (Deitel, 797–799; Josuttis 597)
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Example: Checking Stream StateExample: Checking Stream State
int main(){ int n = 1; char c = 'x';
while( n > 0 ){cout << "Enter an integer: ";cin >> n;if( !cin ){ //check the failbit
cout << "That was not an integer!\n";cin.clear(); //clear the flagscin >> c; //something is still in the streamcout << "You entered " << c << '\n';
}else cout << "You entered " << n << '\n';
}}
Stream I/OStream I/O
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Stream ManipulatorsStream Manipulators
Special objects used to format a stream Used with the stream insertion operator or stream
extraction operator
Stream I/O (Deitel, 781–796; Josuttis, 586)Stream I/O (Deitel, 781–796; Josuttis, 586)
cout << setw(10) << right << "Hello" << endl;
Manipulators that do not require arguments will not need an extra header file.
Manipulators that require arguments will need the <iomanip> header file.
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Some Stream ManipulatorsSome Stream Manipulators
Manipulator Meaning
setw() Set the width of the output
left Left-justify the output
right Right-justify the output
setprecision() Set the number of digits to the right of the decimal point in floating point numbers
showpoint Specifying that floating point numbers are always output with a decimal point
fixed Use fixed-point notation for the output format of floating point numbers
scientific Use scientific notation for the output of floating point numbers
uppercase Set the ‘E’ in scientific notation to uppercase
Stream I/O (Deitel, 781–796; Josuttis, 586)Stream I/O (Deitel, 781–796; Josuttis, 586)
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Member Functions for FormattingMember Functions for Formatting
Streams have member functions that can be used to set their format
• Can be used in combination with stream manipulators• Some member functions do the same thing as the manipulators
Examples:
width(n) • Sets the width of the output to n• Equivalent to the “setw(n)” stream manipulator• cout.width(10);
precision(n) • Sets the width of the output to n• Equivalent to the “setprecision(n)” stream manipulator• cout.precision(2);
Stream I/O (Deitel, 781–796; Josuttis, 586)Stream I/O (Deitel, 781–796; Josuttis, 586)
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Bonus Lab 8Bonus Lab 8
Debugging with MS Visual Studio
Ford and Teorey, Ch. 5
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Debugging MethodsDebugging Methods
Semantic errors• Logic errors in your code• Examples: code that creates an infinite loop, off-by-
one error
Interactive debugger• Can run your program line by line• You can stop program execution at any point and
examine the values of its variables
Debugging (Ford)Debugging (Ford)
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Using the MS Visual StudioInteractive Debugger
Using the MS Visual StudioInteractive Debugger
Use “Debug” mode Step Into
• Executes the next statement• Will start at the first line in main if there’s no breakpoint• If the next statement is a function call, it will enter the function
The yellow arrow• Points to the next statement that will be executed
Step Over• Executes the next statement• If the next statement is a function call, it will skip over the function
Step Out• Will finish execution of a function and run to the next statement
Breakpoint• The line where you want your program to stop execution• Set by clicking in the margin at the left of the line of code
Variables pane• Displays a list of current variables and their values• Auto, Locals, and Watch tabs
Debugging (Ford)Debugging (Ford)
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ReferencesReferences
Deitel, H. M., and P. J. Deitel, C++ How to Program, Fifth Edition. Upper Saddle River, NJ: Prentice Hall, 2005.
Ford, A. R., and T. J. Teorey, Practical Debugging in C++. Upper Saddle River, NJ: Prentice Hall, 2002.
Josuttis, Nicolai M., The C++ Standard Library, A Tutorial and Reference. Boston: Addison-Wesley, 1999.