- •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 14
#include <iostream> #include <iomanip>
using namespace std;
int main(int argc, char** argv)
{
bool myBool = true;
cout << “This should be true: “ << boolalpha << myBool << endl; cout << “This should be 1: “ << noboolalpha << myBool << endl; double dbl = 1.452;
cout << “This should be @@1.452: “ << setw(7) << setfill(‘@’) << dbl << endl;
}
If you don’t care for the concept of manipulators, you can usually get by without them. Streams provide much of the same functionality through equivalent methods like setPrecision(). See Appendix B for details.
Input with Streams
Input streams provide a simple way to read in structured or unstructured data. In this section, the techniques for input are discussed within the context of cin, the console input stream.
Input Basics
There are two easy ways to read data using an input stream. The first is an analog of the << operator that outputs data to an output stream. The corresponding operator for reading data is >>. When you use >> to read data from an input stream, the variable you provide is the storage for the received value. For example, the following program reads a line of input from the user and puts it into a string. Then the string is output back to the console.
#include <iostream> #include <string>
using namespace std;
int main(int argc, char** argv)
{
string userInput; cin >> userInput;
cout << “User input was “ << userInput << endl;
}
By default, the input stream will tokenize values according to white space. For example, if a user runs the previous program and enters hello there as input, only the characters up to the first white space character (the space character in this instance) will be captured into the userInput variable. The output would be:
User input was hello
The >> operator works with different variable types, just like the << operator. For example, to read an integer, the code differs only in the type of the variable:
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Demystifying C++ I/O
#include <iostream> using namespace std;
int main(int argc, char** argv)
{
int userInput; cin >> userInput;
cout << “User input was “ << userInput << endl;
}
You can use input streams to read in multiple values, mixing and matching types as necessary. For example, the following function, an excerpt from a restaurant reservation system, asks the user for a last name and number of people in their party.
void getReservationData()
{
string guestName; int partySize;
cout << “Name and number of guests: “;
cin >> guestName >> partySize;
cout << “Thank you, “ << guestName << “.” << endl; if (partySize > 10) {
cout << “An extra gratuity will apply.” << endl;
}
}
Note that even though the use of cout does not explicitly flush the buffer using endl or flush(), the text will still be written to the console because the use of cin immediately flushes the cout buffer. cin and cout are linked together in this way.
If you get confused between << and >>, just think of the angles as pointing towards their destination. In an input stream, << points toward the stream itself because data are being sent to the stream. In an output stream, >> points toward the variables because data are being stored.
Input Methods
Just like output streams, input streams have several methods that allow a lower level of access than the functionality provided by the more common >> operator.
get()
The get() method allows raw input of data from a stream. The simplest version of get() simply returns the next character in the stream, though other versions exist that read multiple characters at once. () is most commonly used to avoid the automatic tokenization that occurs with the >> operator. For example, the following function reads a name, which can be made up of several words, from an input stream until the end of the stream is reached.
string readName(istream& inStream)
{
string name;
while (inStream.good()) {
int next = inStream.get(); if (next == EOF) break;
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Chapter 14
name += next;// Implicitly convert to a char and append.
}
return name;
}
There are several interesting observations to make about the previous function. First, its parameter is a reference to an istream, not a const reference. The methods that read in data from a stream will change the actual stream (most notably, its position), so they are not const methods. Thus, you can’t call them on a const reference. Second, the return value of get() is stored in an int, not in a char. Because get() can return special noncharacter values such as EOF (end of file), ints are used. When next is appended to the string, it is implicitly converted to a char.
The previous function is a bit strange because there are two ways to get out of the loop. Either the stream can get into a “not good” state, or the end of the stream is reached. A more common pattern for reading from a stream uses a different version of get() that takes a reference to a character and returns a reference to the stream. This pattern takes advantage of the fact that evaluating an input stream within a conditional context will result in true only if the stream is available for additional reading. Encountering an error or reaching the end-of-file both cause the stream to evaluate to false. The underlying details of the conversion operations required to implement this feature are explained in Chapter 16. The following version of the same function is a bit more concise.
string readName(istream& inStream)
{
string name;
char next; while (inStream.get(next)) { name += next;
}
return name;
}
unget()
For most purposes, the correct way to think of an input stream is as a one-way chute. Data falls down the chute and into variables. The unget() method breaks this model in a way by allowing you to push data back up the chute.
A single call to unget() causes the stream to back up by one position, essentially putting the last character read back on the stream.
char ch1, ch2, ch3;
in >> ch1 >> ch2 >> ch3; in.unget();
char testChar; in >> testChar;
// testChar == ch3 at this point
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Demystifying C++ I/O
putback()
putback(), like unget(), lets you move backward by one character in an input stream. The difference is that the putback() method takes the character being placed back on the stream as a parameter:
char ch1;
in >> ch1;
in.putback(ch1);
// ch1 will be the next character read off the stream.
peek ()
The peek() method allows you to preview the next value that would be returned if you were to call get(). To take the chute metaphor perhaps a bit too far, you could think of it as looking up the chute without a value actually falling down it.
peek() is ideal for any situation where you need to look ahead before reading a value. For example, your program may do something different, depending on whether the next value starts with a number, as in the following code snippet.
int next = cin.peek(); if (isdigit(next)) { processNumber();
} else { processText();
}
getline()
Obtaining a single line of data from an input stream is so common that a method exists to do it for you. The getline() method fills a character buffer with a line of data up to the specified size, as in the following code.
char buffer[kBufferSize + 1];
cin.getline(buffer, kBufferSize);
Note that getline() removes the newline character from the stream. However, the resulting string will not include the newline character. There is a form of get() that performs the same operation as getline(), except that it leaves the newline character in the input stream.
There is also a function called getline() that can be used with C++ strings. It is defined in the std namespace and takes a stream reference, a string reference, and an optional delimeter as parameters:
string myString;
std::getline(cin, myString);
Handling Input Errors
Input streams have a number of methods to detect unusual circumstances. Most of the error conditions related to input streams occur when there is no data available to read. For example, the end of stream
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(referred to as end of file, even for nonfile streams) may have been reached. The most common way of querying the state of an input stream is to access it within a conditional, as above. You can also call the good() method, just like an output stream. There is also an eof() method that returns true if the stream has reached its end.
You should also get in the habit of checking the stream state after reading data so that you can recover from bad input.
The following program shows the common pattern for reading data from a stream and handling errors. The program reads numbers from standard input and displays their sum once end of file is reached. Note that in most command-line environments, end of file is indicated on the console with control-D.
#include <iostream> #include <fstream> #include <string>
using namespace std;
int main()
{
int sum = 0;
if (!cin.good()) {
cout << “Standard input is in a bad state!” << endl; exit(1);
}
int number; while (true) {
cin >> number;
if (cin.good()) { sum += number;
} else if (cin.eof()) {
break; // Reached end of file
}else {
//Error!
cin.clear(); // Clear the error state. string badToken;
cin >> badToken; // Consume the bad input.
cerr << “WARNING: Bad input encountered: “ << badToken << endl;
}
}
cout << “The sum is “ << sum << endl;
return 0;
}
Input Manipulators
The built-in input manipulators, described in the list that follows, can be sent to an input stream to customize the way that data is read.
388