Question

Background:

The purpose of this assignment is to practice dealing with exception handling and textual data. Exception handling is a very important part of being an object-oriented programming. Rather returning some kind of int return value every time you tickle an object, C++ programmers expect methods to focus on their task at hand. If something bad happens, C++ programmers expect methods to throw exceptions. When caught, exceptions can be processed. When uncaught, they cause a program to terminate dead in its tracks. The typical pattern in this course is to have class code throw exceptions and driver code catch them. Because of exceptions, when writing client driver code, our try blocks will not be polluted with error processing statements. Our other topic in this unit is string handling. In C++, string is a class and is much much easier to work with as compared to the typical way a C programmers deal with char *. The string class gives us many different methods and the second programming project will ask you to learn some of these new capabilities.

Project 11: Exception FlashDrive

The purpose of this assignment is to work with exceptions. As you may recall, I have provided you with a sample class named FlashDrive ( VS2010 or VS2012 or XCode5 or XCode6 or XCode7 ) which has been diagrammed below. I'd like you to enhance this class so that invoking its methods or operators potentially throw exceptions, rather than just printing error messages to cout. Currently, our favorite exception class is std::logic_error. You can create a logic_error by passing a string value to its constructor. Officially, you should also say #include <stdexcept> to begin working with logic_error, but Visual Studio (being a badly behaved child...) let's you get away with it.

Although the sample driver code might not code for all these circumstances, I would like you to throw exceptions whenever:

a negative number is potentially stored in myStorageCapacity (due to calls to operator - or setCapacity)

a negative number is potentially stored in myStorageUsed (due to calls to operator - or setUsed)

having a myStorageUsed that exceeds myStorageCapacity (due to calls to operator + or writeData or setUsed)

So carefully wind your way thru all the operators and methods of the class ensuring that logic_error gets thrown in each of these circumstances.

HINT: Recall that you can create a logic_error by passing a string message. For example,

  std::logic_error error( "Bad News" );

While not required with Visual Studio, please #include <stdexcept> when working with this class. Linux fans will require this include; its optional for Windows users but won't hurt anything if you do it. Here is a class diagram for logic_error. As I said, it already exists so please make use of it.

FlashDrive

Sample Driver Code

FlashDrive FlashDrive( ); FlashDrive( int capacity, int used, bool pluggedIn ); void plugIn( ); void pullOut( ); void writeData( int amount ); void eraseData( int amount ); void formatDrive( ); int getCapacity( ); void setCapacity( int amount ); int getUsed( ); void setUsed( int amount ); bool isPluggedIn( ); int my_StorageCapacity; int my_StorageUsed; bool my_IsPluggedIn;

FlashDrive drive1( 10, 0, false ); FlashDrive drive2( 20, 0, false ); drive1.plugIn( ); drive1.formatDrive( ); drive1.writeData( 5 ); drive1.pullOut( ); drive2.plugIn( ); drive2.formatDrive( ); drive2.writeData( 1 ); drive2.pullOut( ); FlashDrive combined = drive1 + drive2; cout << "this drive's filled to " << combined.getUsed( ) << endl; FlashDrive other = combined – drive1; cout << "the other drives's filled to " << other.getUsed( ) << endl; if (combined > other) { cout << "looks like combined is bigger..." << endl; } else { cout << "looks like other is bigger..." << endl; } if (drive2 > other) { cout << "looks like drive2 is bigger..." << endl; } else { cout << "looks like other is bigger..." << endl; } if (drive2 < drive1) { cout << "looks like drive2 is smaller..." << endl; } else { cout << "looks like drive1 is smaller..." << endl; } cout << "Here is drive1...." << endl; cout << drive1 << endl; cout << "Let's set drive1...." << endl; cin >> drive1; cout << "Here is drive1. Notice the changes..." << endl; cout << drive1 << endl; // Let's try to get some exceptions... try { drive1.writeData( -1000 ); cout << "This should not print out..." << endl; } catch (std::logic_error) { cout << "Exception correctly caught..." << endl; } try { drive1.setUsed( -1000 ); cout << "This should not print out..." << endl; } catch (std::logic_error) { cout << "Exception correctly caught..." << endl; } try { drive1.setCapacity( -1000 ); cout << "This should not print out..." << endl; } catch (std::logic_error le) { cout << "Exception correctly caught..." << le.what( ) << endl; } try { FlashDrive f( 10, 20, false ); cout << "This should not print out..." << endl; } catch (std::logic_error) { cout << "Exception correctly caught..." << endl; }