17 Jul2006 Todays Objectives Announcements Turn in Homework

17 -Jul-2006 Today’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 1

Stream Input/Output Chapter 15 2

Stream I/O (Deitel, 771; Josuttis, 584) Streams § 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 • 3

Stream I/O (Deitel, 771– 772) 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 4

Stream I/O (Deitel, 772) Header Files <iostream> • • Basic stream I/O services Defines objects: cout, cin, cerr, and clog <iomanip> • Services formatted I/O with stream manipulators <fstream> • Services for file I/O 5

Stream I/O (Deitel, 772– 773; Josuttis, 585) Stream 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 6

Stream I/O (Deitel, 772– 773; Josuttis, 585) Global 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 7

Stream I/O (Deitel, 775– 776; Josuttis, 586) Stream 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 8

Stream I/O (Deitel, 776– 780; Josuttis, 586) Stream 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 class get, getline ignore eof, gcount putback, peek 9

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. 10

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. H buffer e l l o n 11

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. e buffer H l l o n 12

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. l buffer H e l o n 13

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. l buffer H e l o n 14

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. o buffer H e l l n 15

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. Leaves the delimiter in the stream buffer H e l n l o 16

Stream I/O (Deitel, 776– 780) Using get() § Used with no arguments, it inputs one char c = cin. get(); § Can be used with three arguments char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. get(buffer, 1024, 'n'); 1. 2. 3. n buffer H e l l o Inserts ‘’ terminator 17

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); 18

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); cin H buffer e l l o n 19

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); cin e buffer H l l o n 20

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); cin l buffer H e l o n 21

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); cin l buffer H e l o n 22

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); cin o buffer H e l l n 23

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); cin Discards the delimiter in the stream buffer H e l n l o 24

Stream I/O (Deitel, 776– 780) Using getline() § Used with three arguments 1. 2. 3. char array size limit delimiter char (optional: default is ‘n’) char buffer[1024]; cin. getline(buffer, 1024); cin buffer H e l l o Inserts ‘’ terminator 25

Stream I/O (Deitel, 776– 780) 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 • § Example char buffer[1024]; cin. read( buffer, 5 ); cout. write( buffer, 5 ); 26

Stream I/O (Deitel, 766– 768; Josuttis 597) Stream 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 27

Stream I/O (Deitel, 797– 799; Josuttis 597) Determining 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 28

Stream I/O Example: 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 flags cin >> c; //something is still in the stream cout << "You entered " << c << 'n'; } else cout << "You entered " << n << 'n'; } 29

Stream I/O (Deitel, 781– 796; Josuttis, 586) Stream Manipulators § Special objects used to format a stream § Used with the stream insertion operator or stream extraction operator cout << setw(10) << right << "Hello" << endl; Manipulators that require arguments will need the <iomanip> header file. Manipulators that do not require arguments will not need an extra header file. 30

Stream I/O (Deitel, 781– 796; Josuttis, 586) Some Stream Manipulators Manipulator setw() Meaning 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 Specifying that floating point numbers are always output with a decimal point Use fixed-point notation for the output format of floating point numbers Use scientific notation for the output of floating point numbers Set the ‘E’ in scientific notation to uppercase showpoint fixed scientific uppercase 31

Stream I/O (Deitel, 781– 796; Josuttis, 586) Member 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); 32

Bonus Lab 8 Debugging with MS Visual Studio Ford and Teorey, Ch. 5 33

Debugging (Ford) Debugging Methods § Semantic errors Logic errors in your code • Examples: code that creates an infinite loop, off-byone 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 • 34

Debugging (Ford) Using the MS Visual Studio Interactive Debugger § § Use “Debug” mode Step Into • • • § The yellow arrow • § Will finish execution of a function and run to the next statement Breakpoint • • § Executes the next statement If the next statement is a function call, it will skip over the function Step Out • § Points to the next statement that will be executed Step Over • • § 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 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 35

References 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. 36