Write program in C++, C# or Java

Write a program that processes batch requests for updating simple databases. (Imagine

that commands have been saved during the day for an overnight run that actually updates

the databases.) The databases can be simulated using a

map

data structure, using strings

for both keys and values. Here is the Database class interface in C++:

class Database {

map data;

etc.

public:

Database(const string& id);

string getID() const;

void add(const string& key, const string& value);

string get(const string& key) const;

void update(const string& key, const string& value);

void remove(const string& key);

void display(ostream& dest) const; // Writes key|value lines

};

(Note: the above interface may be modified if necessary. And you dont have to use a

map. Its just easiest.)

Each database has a string id that identifies it. You will read a file of commands to update the database. The file has the following layout grammar:

[] | B | E

Here is a sample file:

A one key1 value1

B

A one key2 value two

A one key3 value3

E

A two key4 value four

R one key1

U two key4 value4

Keys contain no spaces but values can.

The command are A (for add), U (for update), and R (for remove). The delimiters B and

E begin and end a transaction, respectively, which means their intervening contents form a macro command. Macro commands should nest i.e., macros can hold other macros.

Keep a list of databases and create a database the first time you encounter a command that references its id. Do not allow an Add command to modify a record whose key already exists. Update should do nothing if the key in its request does not exist. Make all of your commands undoable, including macro commands. The name of the command file should be a command-line argument. After you have read sample commands from a file into a sequence of command objects, process them (i.e., call their execute() methods) and then print all databases (by calling display with a file stream or standard output as argument). Then undo all commands in reverse order, displaying snapshots of the affected database after each undo. Finally, verify that your databases are empty by displaying them once more. If you are using C++, watch for memory leaks. If you are using Java, feel free to just use the toString method for your map container dont fret about the formatting below. Macros execute invisibly, so print a note when a macro begins execution, and another note when it ends execution. Likewise, print a note when undoing a command.

The sample output for the command file above is:

Beginning a Macro

Ending a Macro

Contents of Databases:

Database one:

key2| value two

key3| value3

Database two:

key4| value4

Undid UpdateCommand

key4| value four

Undid RemoveCommand

key1| value1

key2| value two

key3| value3

Undid AddCommand

Begin Undoing Macro

Undid AddCommand

key1| value1

key2| value two

Undid AddCommand

key1| value1

End Undoing Macro

Undid AddCommand

Contents of Databases:

Database one:

Database two:

Note: You need to handle these error conditions. Report them, and dont do anything.

If you try to add something that is already there.

If you try to remove or change something that isnt there.

If you try to undo a command that didnt work.