- •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
Overloading C++ Operators
In order to allow stream objects to be used in Boolean expressions, but prohibit their undesired promotion to int, the basic_ios class defines operator void* instead of operator bool.
A third alternative is to implement operator! and require clients of the class to use only negative comparisons, such as:
if (!smartCell) { cout << “NULL\n”;
}
As you can see, there is a design element to overloading operators. Your decisions about which operators to overload directly influence the ways in which clients can use your classes.
Overloading the Memor y Allocation and
Deallocation Operators
C++ gives you the ability to redefine the way memory allocation and deallocation work in your programs. You can provide this customization both on the global level and the class level. This capability is most useful when you are worried about performance and would like to provide more efficient memory management than is provided by default. For example, instead of going to the default C++ memory allocation each time you need memory, you could write a memory pool allocator that reuses fixed-size chunks of memory. This section explains the subtleties of the memory allocation and deallocation routines and shows you how to customize them. With these tools, you should be able to write a memory pool if the need ever arises.
Unless you know a lot about memory allocation strategies, attempts to overload the memory allocation routines are rarely worth the trouble. Don’t overload them just because it sounds like a neat idea. Only do so if you have a genuine performance or space requirement and the necessary knowledge.
How new and delete Really Work
One of the trickiest aspects of C++ is the details of new and delete. Consider this line of code:
SpreadsheetCell* cell = new SpreadsheetCell();
The new SpreadsheetCell() is called the new expression. It does two things. First, it allocates space for the SpreadsheetCell object by making a call to operator new. Second, it calls the constructor for the object. Only after the constructor has completed does it return the pointer to you.
delete functions similarly. Consider this line of code:
delete cell;
This line is called the delete expression. It first calls the destructor for cell, then calls operator delete to free the memory.
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When you use the keyword new to allocate memory, you are not directly calling operator new. When you use the keyword delete to free memory, you are not directly calling operator delete.
You can overload operator new and operator delete to control memory allocation and deallocation, but you cannot overload the new expression or the delete expression. Thus, you can customize the actual memory allocation and deallocation, but not the calls to the constructor and destructor.
The New Expression and operator new
There are six different forms of the new expression, each of which has a corresponding operator new. You’ve already seen the first four new expressions in Chapters 13 and 15: new, new[], nothrow new, and nothrow new[]. The operator news for each them are defined in the header file <new> and are reproduced here respectively:
void* operator new(size_t size) throw(bad_alloc); // For new void* operator new[](size_t size) throw(bad_alloc); // For new[]
void* operator new(size_t size, const nothrow_t&) throw(); // For nothrow new void* operator new[](size_t size, const nothrow_t&) throw(); // For nothrow new[]
The fifth and sixth forms of new are called placement new (including both single and array forms). They allow you to construct an object in preexisting memory like this:
void* ptr = allocateMemorySomehow();
SpreadsheetCell* cell = new (ptr) SpreadsheetCell();
This feature is a bit obscure, but it’s important to realize that it exists. It can come in handy if you want to implement memory pools such that you reuse memory without freeing it in between. The corresponding operator news look like this:
void* operator new(size_t size, void* p) throw();
void* operator new[](size_t size, void* p) throw();
The Delete Expression and operator delete
There are only two different forms of the delete expression that you can call: delete, and delete[]; there are no nothrow or placement forms. However, there are all six forms of operator delete. Why the asymmetry? The four nothrow and placement forms are used only if an exception is thrown from a constructor. In that case, the operator delete is called that matches the operator new that was used to allocate the memory prior to the constructor call. However, if you delete a pointer normally, delete will call either operator delete or operator delete[] (never the nothrow or placement forms). Practically, this doesn’t really matter: delete never throws an exception anyway, so the nothrow version of operator delete is superfluous, and placement delete should be a no-op. (The memory wasn’t allocated in placement operator new, so there’s nothing to free). Here are the prototypes for the operator delete forms:
void operator delete(void* ptr) throw(); void operator delete[](void* ptr) throw();
void operator delete(void* ptr, const nothrow_t&) throw();
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Overloading C++ Operators
void operator delete[](void* ptr, const nothrow_t&) throw(); void operator delete(void* p, void*) throw();
void operator delete[](void* p, void*) throw();
Overloading operator new and operator delete
You can actually replace the global operator new and operator delete routines if you want. These functions are called for every new expression and delete expression in the program, unless there are more specific routines in individual classes. However, to quote Bjarne Stroustrup, “. . . replacing the global operator new() and operator delete() is not for the fainthearted.” (The C++ Programming Language, third edition). We don’t recommend it either!
If you fail to heed our advice and decide to replace the global operator new, keep in mind that you cannot put any code in the operator that makes a call to new: an infinite loop would result. For example, you cannot write a message to console with cout.
A more useful technique is to overload operator new and operator delete for specific classes. These overloaded operators will be called only when you allocate and deallocate objects of that particular class. Here is an example of a class that overloads the four nonplacement forms of operator new and operator delete:
#include <new> using namespace std;
class MemoryDemo
{
public: MemoryDemo() {} ~MemoryDemo() {}
void* operator new(size_t size) throw(bad_alloc); void operator delete(void* ptr) throw();
void* operator new[](size_t size) throw(bad_alloc); void operator delete[](void* ptr) throw();
void* operator new(size_t size, const nothrow_t&) throw(); void operator delete(void* ptr, const nothrow_t&) throw();
void* operator new[](size_t size, const nothrow_t&) throw(); void operator delete[](void* ptr, const nothrow_t&) throw();
};
Here are simple implementations of these operators that pass the argument through to calls to the global versions of the operators. Note that nothrow is actually a variable of type nothrow_t.
#include “MemoryDemo.h” #include <iostream> using namespace std;
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void* MemoryDemo::operator new(size_t size) throw(bad_alloc)
{
cout << “operator new\n”; return (::operator new(size));
}
void MemoryDemo::operator delete(void* ptr) throw()
{
cout << “operator delete\n”; ::operator delete(ptr);
}
void* MemoryDemo::operator new[](size_t size) throw(bad_alloc)
{
cout << “operator new[]\n”; return (::operator new[](size));
}
void MemoryDemo::operator delete[](void* ptr) throw()
{
cout << “operator delete[]\n”; ::operator delete[](ptr);
}
void* MemoryDemo::operator new(size_t size, const nothrow_t&) throw()
{
cout << “operator new nothrow\n”; return (::operator new(size, nothrow));
}
void MemoryDemo::operator delete(void* ptr, const nothrow_t&) throw()
{
cout << “operator delete nothrow\n”; ::operator delete[](ptr, nothrow);
}
void* MemoryDemo::operator new[](size_t size, const nothrow_t&) throw()
{
cout << “operator new[] nothrow\n”; return (::operator new[](size, nothrow));
}
void MemoryDemo::operator delete[](void* ptr, const nothrow_t&) throw()
{
cout << “operator delete[] nothrow\n”; ::operator delete[](ptr, nothrow);
}
Here is some code that allocates and frees objects of this class in several ways:
#include “MemoryDemo.h”
int main(int argc, char** argv)
{
MemoryDemo* mem = new MemoryDemo();
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