- •Contents
- •Introduction
- •Who This Book Is For
- •What This Book Covers
- •How This Book Is Structured
- •What You Need to Use This Book
- •Conventions
- •Source Code
- •Errata
- •p2p.wrox.com
- •The Basics of C++
- •The Obligatory Hello, World
- •Namespaces
- •Variables
- •Operators
- •Types
- •Conditionals
- •Loops
- •Arrays
- •Functions
- •Those Are the Basics
- •Diving Deeper into C++
- •Pointers and Dynamic Memory
- •Strings in C++
- •References
- •Exceptions
- •The Many Uses of const
- •C++ as an Object-Oriented Language
- •Declaring a Class
- •Your First Useful C++ Program
- •An Employee Records System
- •The Employee Class
- •The Database Class
- •The User Interface
- •Evaluating the Program
- •What Is Programming Design?
- •The Importance of Programming Design
- •Two Rules for C++ Design
- •Abstraction
- •Reuse
- •Designing a Chess Program
- •Requirements
- •Design Steps
- •An Object-Oriented View of the World
- •Am I Thinking Procedurally?
- •The Object-Oriented Philosophy
- •Living in a World of Objects
- •Object Relationships
- •Abstraction
- •Reusing Code
- •A Note on Terminology
- •Deciding Whether or Not to Reuse Code
- •Strategies for Reusing Code
- •Bundling Third-Party Applications
- •Open-Source Libraries
- •The C++ Standard Library
- •Designing with Patterns and Techniques
- •Design Techniques
- •Design Patterns
- •The Reuse Philosophy
- •How to Design Reusable Code
- •Use Abstraction
- •Structure Your Code for Optimal Reuse
- •Design Usable Interfaces
- •Reconciling Generality and Ease of Use
- •The Need for Process
- •Software Life-Cycle Models
- •The Stagewise and Waterfall Models
- •The Spiral Method
- •The Rational Unified Process
- •Software-Engineering Methodologies
- •Extreme Programming (XP)
- •Software Triage
- •Be Open to New Ideas
- •Bring New Ideas to the Table
- •Thinking Ahead
- •Keeping It Clear
- •Elements of Good Style
- •Documenting Your Code
- •Reasons to Write Comments
- •Commenting Styles
- •Comments in This Book
- •Decomposition
- •Decomposition through Refactoring
- •Decomposition by Design
- •Decomposition in This Book
- •Naming
- •Choosing a Good Name
- •Naming Conventions
- •Using Language Features with Style
- •Use Constants
- •Take Advantage of const Variables
- •Use References Instead of Pointers
- •Use Custom Exceptions
- •Formatting
- •The Curly Brace Alignment Debate
- •Coming to Blows over Spaces and Parentheses
- •Spaces and Tabs
- •Stylistic Challenges
- •Introducing the Spreadsheet Example
- •Writing Classes
- •Class Definitions
- •Defining Methods
- •Using Objects
- •Object Life Cycles
- •Object Creation
- •Object Destruction
- •Assigning to Objects
- •Distinguishing Copying from Assignment
- •The Spreadsheet Class
- •Freeing Memory with Destructors
- •Handling Copying and Assignment
- •Different Kinds of Data Members
- •Static Data Members
- •Const Data Members
- •Reference Data Members
- •Const Reference Data Members
- •More about Methods
- •Static Methods
- •Const Methods
- •Method Overloading
- •Default Parameters
- •Inline Methods
- •Nested Classes
- •Friends
- •Operator Overloading
- •Implementing Addition
- •Overloading Arithmetic Operators
- •Overloading Comparison Operators
- •Building Types with Operator Overloading
- •Pointers to Methods and Members
- •Building Abstract Classes
- •Using Interface and Implementation Classes
- •Building Classes with Inheritance
- •Extending Classes
- •Overriding Methods
- •Inheritance for Reuse
- •The WeatherPrediction Class
- •Adding Functionality in a Subclass
- •Replacing Functionality in a Subclass
- •Respect Your Parents
- •Parent Constructors
- •Parent Destructors
- •Referring to Parent Data
- •Casting Up and Down
- •Inheritance for Polymorphism
- •Return of the Spreadsheet
- •Designing the Polymorphic Spreadsheet Cell
- •The Spreadsheet Cell Base Class
- •The Individual Subclasses
- •Leveraging Polymorphism
- •Future Considerations
- •Multiple Inheritance
- •Inheriting from Multiple Classes
- •Naming Collisions and Ambiguous Base Classes
- •Interesting and Obscure Inheritance Issues
- •Special Cases in Overriding Methods
- •Copy Constructors and the Equals Operator
- •The Truth about Virtual
- •Runtime Type Facilities
- •Non-Public Inheritance
- •Virtual Base Classes
- •Class Templates
- •Writing a Class Template
- •How the Compiler Processes Templates
- •Distributing Template Code between Files
- •Template Parameters
- •Method Templates
- •Template Class Specialization
- •Subclassing Template Classes
- •Inheritance versus Specialization
- •Function Templates
- •Function Template Specialization
- •Function Template Overloading
- •Friend Function Templates of Class Templates
- •Advanced Templates
- •More about Template Parameters
- •Template Class Partial Specialization
- •Emulating Function Partial Specialization with Overloading
- •Template Recursion
- •References
- •Reference Variables
- •Reference Data Members
- •Reference Parameters
- •Reference Return Values
- •Deciding between References and Pointers
- •Keyword Confusion
- •The const Keyword
- •The static Keyword
- •Order of Initialization of Nonlocal Variables
- •Types and Casts
- •typedefs
- •Casts
- •Scope Resolution
- •Header Files
- •C Utilities
- •Variable-Length Argument Lists
- •Preprocessor Macros
- •How to Picture Memory
- •Allocation and Deallocation
- •Arrays
- •Working with Pointers
- •Array-Pointer Duality
- •Arrays Are Pointers!
- •Not All Pointers Are Arrays!
- •Dynamic Strings
- •C-Style Strings
- •String Literals
- •The C++ string Class
- •Pointer Arithmetic
- •Custom Memory Management
- •Garbage Collection
- •Object Pools
- •Function Pointers
- •Underallocating Strings
- •Memory Leaks
- •Double-Deleting and Invalid Pointers
- •Accessing Out-of-Bounds Memory
- •Using Streams
- •What Is a Stream, Anyway?
- •Stream Sources and Destinations
- •Output with Streams
- •Input with Streams
- •Input and Output with Objects
- •String Streams
- •File Streams
- •Jumping around with seek() and tell()
- •Linking Streams Together
- •Bidirectional I/O
- •Internationalization
- •Wide Characters
- •Non-Western Character Sets
- •Locales and Facets
- •Errors and Exceptions
- •What Are Exceptions, Anyway?
- •Why Exceptions in C++ Are a Good Thing
- •Why Exceptions in C++ Are a Bad Thing
- •Our Recommendation
- •Exception Mechanics
- •Throwing and Catching Exceptions
- •Exception Types
- •Throwing and Catching Multiple Exceptions
- •Uncaught Exceptions
- •Throw Lists
- •Exceptions and Polymorphism
- •The Standard Exception Hierarchy
- •Catching Exceptions in a Class Hierarchy
- •Writing Your Own Exception Classes
- •Stack Unwinding and Cleanup
- •Catch, Cleanup, and Rethrow
- •Use Smart Pointers
- •Common Error-Handling Issues
- •Memory Allocation Errors
- •Errors in Constructors
- •Errors in Destructors
- •Putting It All Together
- •Why Overload Operators?
- •Limitations to Operator Overloading
- •Choices in Operator Overloading
- •Summary of Overloadable Operators
- •Overloading the Arithmetic Operators
- •Overloading Unary Minus and Unary Plus
- •Overloading Increment and Decrement
- •Overloading the Subscripting Operator
- •Providing Read-Only Access with operator[]
- •Non-Integral Array Indices
- •Overloading the Function Call Operator
- •Overloading the Dereferencing Operators
- •Implementing operator*
- •Implementing operator->
- •What in the World Is operator->* ?
- •Writing Conversion Operators
- •Ambiguity Problems with Conversion Operators
- •Conversions for Boolean Expressions
- •How new and delete Really Work
- •Overloading operator new and operator delete
- •Overloading operator new and operator delete with Extra Parameters
- •Two Approaches to Efficiency
- •Two Kinds of Programs
- •Is C++ an Inefficient Language?
- •Language-Level Efficiency
- •Handle Objects Efficiently
- •Use Inline Methods and Functions
- •Design-Level Efficiency
- •Cache as Much as Possible
- •Use Object Pools
- •Use Thread Pools
- •Profiling
- •Profiling Example with gprof
- •Cross-Platform Development
- •Architecture Issues
- •Implementation Issues
- •Platform-Specific Features
- •Cross-Language Development
- •Mixing C and C++
- •Shifting Paradigms
- •Linking with C Code
- •Mixing Java and C++ with JNI
- •Mixing C++ with Perl and Shell Scripts
- •Mixing C++ with Assembly Code
- •Quality Control
- •Whose Responsibility Is Testing?
- •The Life Cycle of a Bug
- •Bug-Tracking Tools
- •Unit Testing
- •Approaches to Unit Testing
- •The Unit Testing Process
- •Unit Testing in Action
- •Higher-Level Testing
- •Integration Tests
- •System Tests
- •Regression Tests
- •Tips for Successful Testing
- •The Fundamental Law of Debugging
- •Bug Taxonomies
- •Avoiding Bugs
- •Planning for Bugs
- •Error Logging
- •Debug Traces
- •Asserts
- •Debugging Techniques
- •Reproducing Bugs
- •Debugging Reproducible Bugs
- •Debugging Nonreproducible Bugs
- •Debugging Memory Problems
- •Debugging Multithreaded Programs
- •Debugging Example: Article Citations
- •Lessons from the ArticleCitations Example
- •Requirements on Elements
- •Exceptions and Error Checking
- •Iterators
- •Sequential Containers
- •Vector
- •The vector<bool> Specialization
- •deque
- •list
- •Container Adapters
- •queue
- •priority_queue
- •stack
- •Associative Containers
- •The pair Utility Class
- •multimap
- •multiset
- •Other Containers
- •Arrays as STL Containers
- •Strings as STL Containers
- •Streams as STL Containers
- •bitset
- •The find() and find_if() Algorithms
- •The accumulate() Algorithms
- •Function Objects
- •Arithmetic Function Objects
- •Comparison Function Objects
- •Logical Function Objects
- •Function Object Adapters
- •Writing Your Own Function Objects
- •Algorithm Details
- •Utility Algorithms
- •Nonmodifying Algorithms
- •Modifying Algorithms
- •Sorting Algorithms
- •Set Algorithms
- •The Voter Registration Audit Problem Statement
- •The auditVoterRolls() Function
- •The getDuplicates() Function
- •The RemoveNames Functor
- •The NameInList Functor
- •Testing the auditVoterRolls() Function
- •Allocators
- •Iterator Adapters
- •Reverse Iterators
- •Stream Iterators
- •Insert Iterators
- •Extending the STL
- •Why Extend the STL?
- •Writing an STL Algorithm
- •Writing an STL Container
- •The Appeal of Distributed Computing
- •Distribution for Scalability
- •Distribution for Reliability
- •Distribution for Centrality
- •Distributed Content
- •Distributed versus Networked
- •Distributed Objects
- •Serialization and Marshalling
- •Remote Procedure Calls
- •CORBA
- •Interface Definition Language
- •Implementing the Class
- •Using the Objects
- •A Crash Course in XML
- •XML as a Distributed Object Technology
- •Generating and Parsing XML in C++
- •XML Validation
- •Building a Distributed Object with XML
- •SOAP (Simple Object Access Protocol)
- •. . . Write a Class
- •. . . Subclass an Existing Class
- •. . . Throw and Catch Exceptions
- •. . . Read from a File
- •. . . Write to a File
- •. . . Write a Template Class
- •There Must Be a Better Way
- •Smart Pointers with Reference Counting
- •Double Dispatch
- •Mix-In Classes
- •Object-Oriented Frameworks
- •Working with Frameworks
- •The Model-View-Controller Paradigm
- •The Singleton Pattern
- •Example: A Logging Mechanism
- •Implementation of a Singleton
- •Using a Singleton
- •Example: A Car Factory Simulation
- •Implementation of a Factory
- •Using a Factory
- •Other Uses of Factories
- •The Proxy Pattern
- •Example: Hiding Network Connectivity Issues
- •Implementation of a Proxy
- •Using a Proxy
- •The Adapter Pattern
- •Example: Adapting an XML Library
- •Implementation of an Adapter
- •Using an Adapter
- •The Decorator Pattern
- •Example: Defining Styles in Web Pages
- •Implementation of a Decorator
- •Using a Decorator
- •The Chain of Responsibility Pattern
- •Example: Event Handling
- •Implementation of a Chain of Responsibility
- •Using a Chain of Responsibility
- •Example: Event Handling
- •Implementation of an Observer
- •Using an Observer
- •Chapter 1: A Crash Course in C++
- •Chapter 3: Designing with Objects
- •Chapter 4: Designing with Libraries and Patterns
- •Chapter 5: Designing for Reuse
- •Chapter 7: Coding with Style
- •Chapters 8 and 9: Classes and Objects
- •Chapter 11: Writing Generic Code with Templates
- •Chapter 14: Demystifying C++ I/O
- •Chapter 15: Handling Errors
- •Chapter 16: Overloading C++ Operators
- •Chapter 17: Writing Efficient C++
- •Chapter 19: Becoming Adept at Testing
- •Chapter 20: Conquering Debugging
- •Chapter 24: Exploring Distributed Objects
- •Chapter 26: Applying Design Patterns
- •Beginning C++
- •General C++
- •I/O Streams
- •The C++ Standard Library
- •C++ Templates
- •Integrating C++ and Other Languages
- •Algorithms and Data Structures
- •Open-Source Software
- •Software-Engineering Methodology
- •Programming Style
- •Computer Architecture
- •Efficiency
- •Testing
- •Debugging
- •Distributed Objects
- •CORBA
- •XML and SOAP
- •Design Patterns
- •Index
Chapter 21
mAccounts.erase(acctNum);
}
BankAccount& BankDB::findAccount(int acctNum) throw(out_of_range)
{
//Finding an element via its key can be done with find(). map<int, BankAccount>::iterator it = mAccounts.find(acctNum); if (it == mAccounts.end()) {
throw (out_of_range(“No account with that number.”));
}
//Remember that iterators into maps refer to pairs of key/value. return (it->second);
}
BankAccount& BankDB::findAccount(const string& name) throw(out_of_range)
{
//
//Finding an element by a non-key attribute requires a linear
//search through the elements.
//
for (map<int, BankAccount>::iterator it = mAccounts.begin(); it != mAccounts.end(); ++it) {
if (it->second.getClientName() == name) { // Found it!
return (it->second);
}
}
throw (out_of_range(“No account with that name.”));
}
void BankDB::mergeDatabase(BankDB& db)
{
//Just insert copies of all the accounts in the old db
//into the new one. mAccounts.insert(db.mAccounts.begin(), db.mAccounts.end());
//Now delete all the accounts in the old one. db.mAccounts.clear();
}
multimap
The multimap is a map that allows multiple elements with the same key. The interface is almost identical to the map interface, with the following changes:
multimaps do not provide operator[]. The semantics of this operator do not make sense if there can be multiple elements with a single key.
Inserts on multimaps always succeed. Thus, the multimap insert() that adds a single element doesn’t need to return the pair of the iterator and bool. It returns only the iterator.
multimaps allow you to insert identical key/value pairs. If you want to avoid this redundancy, you must check explicitly before inserting a new element.
604
Delving into the STL: Containers and Iterators
The trickiest aspect of multimaps is looking up elements. You can’t use operator[], because it is not provided. find() isn’t very useful because it returns an iterator referring to any one of the elements with a given key (not necessarily the first element with that key).
Luckily, multimaps store all elements with the same key together and provide methods to obtain iterators for this subrange of elements with the same key in the container. lower_bound() and upper_bound() each return a single iterator referring to the first and one-past-the-last elements matching a given key. If there are no elements matching that key, the iterators returned by lower_bound() and upper_bound() will be equal to each other.
In case you don’t want to call two separate methods to obtain the iterators bounding the elements with a given key, multimaps also provide equal_range(), which returns a pair of the two iterators that would be returned by lower_bound() and upper_bound().
The example in the next section illustrates the use of these methods.
The lower_bound(), upper_bound(), and equal_range() methods exist for maps as well, but their usefulness is limited.
multimap Example: Buddy Lists
Most of the numerous online chat programs allow users to have a “buddy list” or list of friends. The chat program confers special privileges on users in the buddy list, such as allowing them to send unsolicited messages to the user.
One way to implement the buddy lists for an online chat program is to store the information in a multimap. One multimap could store the buddy lists for every user. Each entry in the container stores one buddy for a user. The key is the user and the value is the buddy. For example, if the two authors of this book had each other on their individual buddy lists, there would be two entries of the form “Nicholas Solter” maps to “Scott Kleper” and “Scott Kleper” maps to “Nicholas Solter.” The multimap allows multiple values for the same key, so the same user is allowed multiple buddies. Here the BuddyList class definition:
#include <map> #include <string> #include <list>
using std::multimap; using std::string; using std::list;
class BuddyList
{
public:
BuddyList();
//
// Adds buddy as a friend of name
//
void addBuddy(const string& name, const string& buddy);
605
Chapter 21
//
// Removes buddy as a friend of name
//
void removeBuddy(const string& name, const string& buddy);
//
//Returns true if buddy is a friend of name.
//Otherwise returns false.
//
bool isBuddy(const string& name, const string& buddy) const;
//
// Retrieves a list of all the friends of name
//
list<string> getBuddies(const string& name) const;
protected:
multimap<string, string> mBuddies; private:
// Prevent assignment and pass-by-value. BuddyList(const BuddyList& src); BuddyList& operator=(const BuddyList& rhs);
};
Here is the implementation. It demonstrates the use of lower_bound(), upper_bound(), and equal_range():
#include “BuddyList.h” using namespace std;
BuddyList::BuddyList()
{
}
void BuddyList::addBuddy(const string& name, const string& buddy)
{
//Make sure this buddy isn’t already there.
//We don’t want to insert an identical copy of the
//key/value pair.
if (!isBuddy(name, buddy)) { mBuddies.insert(make_pair(name, buddy));
}
}
void BuddyList::removeBuddy(const string& name, const string& buddy)
{
//Declare two iterators into the map. multimap<string, string>::iterator start, end;
//Obtain the beginning and end of the range of elements with
//key name. Use both lower_bound() and upper_bound() to demonstrate
//their use. Otherwise, could just call equal_range().
start = mBuddies.lower_bound(name); end = mBuddies.upper_bound(name);
606
Delving into the STL: Containers and Iterators
//Iterate through the elements with key name looking
//for a value buddy.
for (start; start != end; ++start) { if (start->second == buddy) {
// We found a match! Remove it from the map. mBuddies.erase(start);
break;
}
}
}
bool BuddyList::isBuddy(const string& name, const string& buddy) const
{
//Declare two iterators into the map. multimap<string, string>::const_iterator start, end;
//Obtain the beginning and end of the range of elements with
//key name. Use both lower_bound() and upper_bound() to demonstrate
//their use. Otherwise, could just call equal_range().
start = mBuddies.lower_bound(name); end = mBuddies.upper_bound(name);
//Iterate through the elements with key name looking
//for a value buddy. If there are no elements with key name,
//start equals end, so the loop body doesn’t execute.
for (start; start != end; ++start) { if (start->second == buddy) {
// We found a match! return (true);
}
}
// No matches return (false);
}
list<string> BuddyList::getBuddies(const string& name) const
{
//Create a variable to store the pair of iterators. pair<multimap<string, string>::const_iterator,
multimap<string, string>::const_iterator> its;
//Obtain the pair of iterators marking the range containing
//elements with key name.
its = mBuddies.equal_range(name);
//Create a list with all the names in the range
//(all the buddies of name).
list<string> buddies;
for (its.first; its.first != its.second; ++its.first) { buddies.push_back((its.first)->second);
}
return (buddies);
}
607
Chapter 21
Note that removeBuddy() can’t simply use the version of erase() that erases all elements with a given key, because it should erase only one element with the key, not all of them. Note also that getBuddies() can’t use insert() on the list to insert the elements in the range returned by equal_range(), because the elements referred to by the multimap iterators are key/value pairs, not strings. getBuddies() must iterate explicitly through the list extracting the string from each key/value pair and pushing it onto the new list to be returned.
Here is a simple test of the BuddyList:
#include “BuddyList.h” #include <iostream> using namespace std;
int main(int argc, char** argv)
{
BuddyList buddies;
buddies.addBuddy(“Harry Potter”, “Ron Weasley”); buddies.addBuddy(“Harry Potter”, “Hermione Granger”); buddies.addBuddy(“Harry Potter”, “Hagrid”); buddies.addBuddy(“Harry Potter”, “Draco Malfoy”);
// That’s not right! Remove Draco. buddies.removeBuddy(“Harry Potter”, “Draco Malfoy”);
buddies.addBuddy(“Hagrid”, “Harry Potter”); buddies.addBuddy(“Hagrid”, “Ron Weasley”); buddies.addBuddy(“Hagrid”, “Hermione Granger”);
list<string> harryBuds = buddies.getBuddies(“Harry Potter”);
cout << “Harry’s friends: \n”;
for (list<string>::const_iterator it = harryBuds.begin(); it != harryBuds.end(); ++it) {
cout << “\t” << *it << endl;
}
return (0);
}
set
The set container is very similar to the map. The difference is that instead of storing key/value pairs, in sets the value itself is the key. sets are useful for storing information in which there is no explicit key, but that you want sorted for quick insertion, lookup, and deletion.
The interface supplied by set is almost identical to that of the map. The main difference is that the set doesn’t provide operator[]. Also, although the standard doesn’t state it explicitly, most implementations make the set iterator identical to const_iterator, such that you can’t modify the elements of the set through the iterator. Even if your version of the STL permits you to modify set elements through an iterator, you should avoid doing so because modifying elements of the set while they are in the container would destroy the sorted order.
608
Delving into the STL: Containers and Iterators
set Example: Access Control List
One way to implement basic security on a computer system is through access control lists. Each entity on the system, such as a file or a device, has a list of users with permissions to access that entity. Users can generally be added to and removed from the permissions list for an entity only by users with special privileges. Internally, the set container provides a nice way to represent the access control list. You could use one set for each entity, containing all the usernames who are allowed to access the entity. Here is a class definition for a simple access control list:
#include <set> #include <string> #include <list> using std::set; using std::string; using std::list;
class AccessList
{
public: AccessList() {}
//
// Adds the user to the permissions list
//
void addUser(const string& user);
//
// Removes the user from the permissions list
//
void removeUser(const string& user);
//
// Returns true if user is in the permissions list
//
bool isAllowed(const string& user) const;
//
// Returns a list of all the users who have permissions
//
list<string> getAllUsers() const;
protected:
set<string> mAllowed;
};
Here are the method definitions.
#include “AccessList.h” using namespace std;
void AccessList::addUser(const string& user)
{
mAllowed.insert(user);
}
609