- •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
//
//Remove students who are on the dropped list.
//Iterate through the dropped list, calling remove on the
//master list for each student in the dropped list.
//
for (list<string>::const_iterator it = droppedStudents.begin(); it != droppedStudents.end(); ++it) { allStudents.remove(*it);
}
// Done!
return (allStudents);
}
Container Adapters
In addition to the three standard sequential containers, the STL provides three container adapters: the queue, priority_queue, and stack. Each of these adapters is a wrapper around one of the sequential containers. The intent is to simplify the interface and to provide only those features that are appropriate for the stack or queue abstraction. For example, the adapters don’t provide iterators or the capability to insert or erase multiple elements simultaneously.
The container adapters’ interfaces may be too limiting for your needs. If so, you can use the sequential containers directly or write your own, more full-featured, adapters. See Chapter 26 for details on the adapter design pattern.
queue
The queue container adapter, defined in the header file <queue>, provides standard “first-in, first-out” (FIFO) semantics. As usual, it’s written as a class template, which looks like this:
template <typename T, typename Container = deque<T> > class queue;
The T template parameter specifies the type that you intend to store in the queue. The second template parameter allows you to stipulate the underlying container that the queue adapts. However, the queue requires the sequential container to support both push_back() and pop_front(), so you only have two built-in choices: deque and list. For most purposes, you can just stick with the default deque.
Queue Operations
The queue interface is extremely simple: there are only six methods plus the constructor and the normal comparison operators. The push() method adds a new element to the tail of the queue, and pop() removes the element at the head of the queue. You can retrieve references to, without removing, the first and last elements with front() and back(), respectively. As usual, when called on const objects, front() and back() return const references, and when called on non-const objects they return non-const (read/write) references.
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pop() does not return the element popped. If you want to retain a copy, you must first retrieve it with front().
The queue also supports size() and empty(). See the Standard Library Reference resource on the Web site for details.
Queue Example: A Network Packet Buffer
When two computers communicate over a network, they send information to each other divided up into discrete chunks called packets. The networking layer of the computer’s operating system must pick up the packets and store them as they arrive. However, the computer might not have enough bandwidth to process all of them at once. Thus, the networking layer usually buffers, or stores, the packets until the higher layers have a chance to attend to them. The packets should be processed in the order they arrive, so this problem is perfect for a queue structure. Following is a small PacketBuffer class that stores incoming packets in a queue until they are processed. It’s a template so that different layers of the networking layer can use it for different kinds of packets, such as IP packets or TCP packets. It allows the client to specify a max size because operating systems usually limit the number of packets that can be stored, so as not to use too much memory. When the buffer is full, subsequently arriving packets are ignored
#include <queue> #include <stdexcept> using std::queue;
template <typename T> class PacketBuffer
{
public:
//
//If maxSize is nonpositive, the size is unlimited.
//Otherwise only maxSize packets are allowed in
//the buffer at any one time.
//
PacketBuffer(int maxSize = -1);
//
//Stores the packet in the buffer.
//Throws overflow_error is the buffer is full.
void bufferPacket(const T& packet);
//
//Returns the next packet. Throws out_of_range
//if the buffer is empty.
//
T getNextPacket() throw (std::out_of_range);
protected:
queue<T> mPackets; int mMaxSize;
private:
// Prevent assignment and pass-by-value.
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Chapter 21
PacketBuffer(const PacketBuffer& src); PacketBuffer& operator=(const PacketBuffer& rhs);
};
template <typename T> PacketBuffer<T>::PacketBuffer(int maxSize)
{
mMaxSize = maxSize;
}
template <typename T>
void PacketBuffer<T>::bufferPacket(const T& packet)
{
if (mMaxSize > 0 && mPackets.size() == static_cast<size_t>(mMaxSize)) {
// No more space. Just drop the packet. return;
}
mPackets.push(packet);
}
template <typename T>
T PacketBuffer<T>::getNextPacket() throw (std::out_of_range)
{
if (mPackets.empty()) {
throw (std::out_of_range(“Buffer is empty”));
}
//Retrieve the head element. T temp = mPackets.front();
//Pop the head element. mPackets.pop();
//Return the head element. return (temp);
}
A practical application of this class would require multiple threads. However, here is a quick unit testlike example of its use:
#include “PacketBuffer.h” #include <iostream> using namespace std;
class IPPacket {};
int main(int argc, char** argv)
{
PacketBuffer<IPPacket> ipPackets(3);
ipPackets.bufferPacket(IPPacket());
ipPackets.bufferPacket(IPPacket());
ipPackets.bufferPacket(IPPacket());
ipPackets.bufferPacket(IPPacket());
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while (true) { try {
IPPacket packet = ipPackets.getNextPacket(); } catch (out_of_range&) {
cout << “Processed all packets!” << endl;
break;
}
}
return (0);
}
priority_queue
A priority queue is a queue that keeps its elements in sorted order. Instead of a strict FIFO ordering, the element at the head of queue at any given time is the one with the highest priority. This element could be the oldest on the queue or the most recent. If two elements have equal priority, their relative order in the queue is FIFO.
The STL priority_queue container adapter is also defined in <queue>. Its template definition looks something like this (slightly simplified) one:
template <typename T, typename Container = vector<T>, typename Compare =
less<T> >;
It’s not as complicated as it looks! You’ve seen the first two parameters before: T is the element type stored in the priority_queue and Container is the underlying container on which the priority_queue is adapted. The priority_queue uses vector as the default, but deque works as well. list does not work because the priority_queue requires random access to its elements for sorting them. The third parameter, Compare, is trickier. As you’ll learn more about in Chapter 22, less is a class template that supports comparison of two objects of type T with operator<. What this means for you is that the priority of elements in the queue is determined according to operator<. You can customize the comparison used, but that’s a topic for Chapter 22. For now, just make sure that you define operator< appropriately for the types stored in the priority_queue.
The head element of the priority queue is the one with the “highest” priority, by default determined according to operator< such that elements that are “less” than other elements have lower priority.
Priority Queue Operations
The priority_queue provides even fewer operations than does the queue. push() and pop() allow you to insert and remove elements respectively, and top() returns a const reference to the head element.
top() returns a const reference even when called on a non-const object. The priority_queue provides no mechanism to obtain the tail element.
pop() does not return the element popped. If you want to retain a copy, you must first retrieve it with top().
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Like the queue, the priority_queue supports size() and empty(). However, it does not provide any comparison operators. The Standard Library Reference resource on the Web site for details.
This interface is obviously limited. In particular, the priority_queue provides no iterator support, and it is impossible to merge two priority_queues.
Priority Queue Example: An Error Correlator
Single failures on a system can often cause multiple errors to be generated from different components. A good error-handling system uses error correlation to avoid processing duplicate errors and to process the most important errors first. You can use a priority_queue to write a very simple error correlator. This class simply sorts events according to their priority, so that the highest-priority errors are always processed first. Here is the class definition:
#include <ostream> #include <string> #include <queue> #include <stdexcept>
// Sample Error class with just a priority and a string error description class Error
{
public:
Error(int priority, std::string errMsg) : mPriority(priority), mError(errMsg) {}
int getPriority() const {return mPriority; } std::string getErrorString() const {return mError; }
friend bool operator<(const Error& lhs, const Error& rhs);
friend std::ostream& operator<<(std::ostream& str, const Error& err);
protected:
int mPriority; std::string mError;
};
// Simple ErrorCorrelator class that returns highest priority errors first class ErrorCorrelator
{
public: ErrorCorrelator() {}
//
// Add an error to be correlated.
//
void addError(const Error& error);
//
// Retrieve the next error to be processed.
//
Error getError() throw (std::out_of_range);
protected:
std::priority_queue<Error> mErrors;
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Delving into the STL: Containers and Iterators
private:
// Prevent assignment and pass-by-reference. ErrorCorrelator(const ErrorCorrelator& src); ErrorCorrelator& operator=(const ErrorCorrelator& rhs);
};
Here are the definitions of the functions and methods.
#include “ErrorCorrelator.h” using namespace std;
bool operator<(const Error& lhs, const Error& rhs)
{
return (lhs.mPriority < rhs.mPriority);
}
ostream& operator<<(ostream& str, const Error& err)
{
str << err.mError << “ (priority “ << err.mPriority << “)”; return (str);
}
void ErrorCorrelator::addError(const Error& error)
{
mErrors.push(error);
}
Error ErrorCorrelator::getError() throw (out_of_range)
{
//
//If there are no more errors, throw an exception.
if (mErrors.empty()) {
throw (out_of_range(“No elements!”));
}
//Save the top element.
Error top = mErrors.top();
//Remove the top element. mErrors.pop();
//Return the saved element. return (top);
}
Here is a simple unit test showing how to use the ErrorCorrelator. Realistic use would require multiple threads so that one thread adds errors, while another processes them.
#include “ErrorCorrelator.h” #include <iostream>
using namespace std;
int main(int argc, char** argv)
{
ErrorCorrelator ec;
593