- •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
Effective Memory Management
Dynamic Strings
Strings present something of a quandary for programming language designers because they seem like a standard data type, but are not expressed in fixed sizes. Strings are so commonly used, however, that most programming languages need to have a built-in model of a string. In the C language, strings are somewhat of a hack, never given the first-class language feature attention that they deserve. C++ provides a far more flexible and useful representation of a string.
C-Style Strings
In the C language, strings are represented as an array of characters. The last character of a string is a null character (‘\0’) so that code operating on the string can determine where it ends. Even though C++ provides a better string abstraction, it is important to understand the C technique for strings because they still arise in C++ programming.
By far, the most common mistake that programmers make with C strings is that they forget to allocate space for the ‘\0’ character. For example, the string “hello” appears to be five characters long, but six characters worth of space are needed in memory to store the value, as shown in Figure 13-13.
Stack |
Heap |
myString 'h'
'e'
'l'
'l'
'o'
'\0'
Figure 13-13
C++ contains several functions from the C language that operate on strings. As a general rule of thumb, these functions do not handle memory allocation. For example, the strcpy() function takes two strings as parameters. It copies the second string onto the first, whether it fits or not. The following code attempts to build a wrapper around strcpy() that allocates the correct amount of memory and returns the result, instead of taking in an already allocated string. It uses the strlen() function to obtain the length of the string.
char* copyString(const char* inString)
{
char* result = new char[strlen(inString)]; // BUG! Off by one!
strcpy(result, inString);
return result;
}
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The copyString() function as written is incorrect. The strlen() function returns the length of the string, not the amount of memory needed to hold it. For the string “hello”, strlen() will return 5, not 6! The proper way to allocate memory for a string is to add one to the amount of space needed for the actual characters. It seems a little weird at first to have +1 all over, but it quickly becomes natural, and you (hopefully) miss it when it’s not there.
char* copyString(const char* inString)
{
char* result = new char[strlen(inString) + 1];
strcpy(result, inString);
return result;
}
One way to remember that strlen() only returns the number of actual characters in the string is to consider what would happen if you were allocating space for a string made up of several others. For example, if your function took in three strings and returned a string that was the concatenation of all three, how big would it be? To hold exactly enough space, it would be the length of all three strings, added together, plus one for the trailing ‘\0’ character. If strlen() included the ‘\0’ in the length of the string, the allocated memory would be too big. The following code uses the strcpy() and strcat() functions to perform this operation.
char* appendStrings(const char* inStr1, const char* inStr2, const char* inStr3)
{
char* result = new char[strlen(inStr1) + strlen(inStr2) + strlen(inStr3) + 1];
strcpy(result, inStr1);
strcat(result, inStr2); strcat(result, inStr3);
return result;
}
A complete list of C functions to operate on strings is found in the <cstring> header file.
String Literals
You’ve probably seen strings written in a C++ program with quotes around them. For example, the following code outputs the string hello by including the string itself, not a variable that contains it.
cout << “hello” << endl;
In the preceding line, “hello” is a string literal because it is written as a value, not a variable. Even though string literals don’t have associated variables, they are treated as const char*’s (arrays of constant characters).
String literals can be assigned to variables, but doing so can be risky. The actual memory associated with a string literal is in a read-only part of memory, which is why it is an array of constant characters. This
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allows the compiler to optimize memory usage by reusing references to equivalent string literals (that is, even if your program uses the string literal “hello” 500 times, the compiler can create just one instance of hello in memory). The compiler does not, however, force your program to assign a string literal only to a variable of type const char* or const char[]. You can assign a string to a char* without const, and the program will work fine unless you attempt to change the string. Generally, attempting to change the string will immediately crash your program, as demonstrated in the following code:
char* ptr = “hello”; |
// |
Assign |
the string literal to a variable. |
ptr[1] = ‘a’; |
// |
CRASH! |
Attempts to write to read-only memory |
|
|
|
|
A much safer way to code is to use a pointer to const characters when referring to string literals. The code below contains the same bug, but because it assigned the literal to a const character array, the compiler will catch the attempt to write to read-only memory.
const char* ptr = “hello”; |
// |
Assign the string literal |
to a variable. |
ptr[1] = ‘a’; |
// |
BUG! Attempts to write to |
read-only memory |
|
|
|
|
You can also use a string literal as an initial value for a stack-based character array. Because the stackbased variable cannot in any way refer to memory somewhere else, the compiler will take care of copying the string literal into the stack-based array memory.
char stackArray[] = “hello”; // Compiler takes care of copying the array and // creating appropriate size for stack array
stackArray[1] = ‘a’; |
// The copy can be modified. |
The C++ string Class
As we promised earlier, C++ provides a much-improved implementation of a string as part of the Standard Library. In C++, string is a class (actually an instantiation of the basic_string template class) that supports many of the same operations as the <cstring> functions but, best of all, takes care of memory allocation for you if you use it properly.
What Was Wrong with C-Style Strings?
Before jumping into the new world of the C++ string class, consider the advantages and disadvantages of C-style strings.
Advantages:
They are simple, making use of the underlying basic character type and array structure.
They are lightweight, taking up only the memory that they need if used properly.
They are low level, so you can easily manipulate and copy them as raw memory.
They are well understood by C programmers — why learn something new?
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Disadvantages:
They are unforgiving and susceptible to difficult memory bugs.
They don’t leverage the object-oriented nature of C++.
They come with a set of poorly named and sometimes confusing helper functions.
They require knowledge of their underlying representation on the part of the programmer.
The preceding lists were carefully constructed to make you think that perhaps there is a better way. As you’ll learn below, C++ strings solve all of these disadvantages of C strings and make the advantages moot.
Using the string Class
Even though string is a class, you can almost always treat it as though it were a built-in type, like int. In fact, the more you think of it as a simple type, the better off you are. Programmers generally encounter the least trouble with string when they forget that strings are objects.
Through the magic of operator overloading, C++ strings support concatenation with the + operator, assignment with the = operator, comparison with the == operator, and individual character access with the [] operator. These operators are what allow the programmer to treat string like a basic type. As the following code shows, you can perform these operations on a string without worrying about memory allocation.
int main(int argc, char** argv)
{
string myString = “hello”;
myString += “, there”;
string myOtherString = myString;
if (myString == myOtherString) { myOtherString[0] = ‘H’;
}
cout << myString << endl; cout << myOtherString << endl;
}
The output of this code is:
hello, there Hello, there
There are several things to note in this example. First, there are no memory leaks even though strings are allocated and resized left and right. All of these string objects were created as stack variables. While the string class certainly had a bunch of allocating and resizing to do, the objects themselves cleaned up this memory when they went out of scope.
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