- •Table of Contents
- •Introduction
- •What Is C++?
- •Conventions Used in This Book
- •How This Book Is Organized
- •Part I: Introduction to C++ Programming
- •Part III: Introduction to Classes
- •Part IV: Inheritance
- •Part V: Optional Features
- •Part VI: The Part of Tens
- •Icons Used in This Book
- •Where to Go from Here
- •Grasping C++ Concepts
- •How do I program?
- •Installing Dev-C++
- •Setting the options
- •Creating Your First C++ Program
- •Entering the C++ code
- •Building your program
- •Executing Your Program
- •Dev-C++ is not Windows
- •Dev-C++ help
- •Reviewing the Annotated Program
- •Examining the framework for all C++ programs
- •Clarifying source code with comments
- •Basing programs on C++ statements
- •Writing declarations
- •Generating output
- •Calculating Expressions
- •Storing the results of expression
- •Declaring Variables
- •Declaring Different Types of Variables
- •Reviewing the limitations of integers in C++
- •Solving the truncation problem
- •Looking at the limits of floating-point numbers
- •Declaring Variable Types
- •Types of constants
- •Special characters
- •Are These Calculations Really Logical?
- •Mixed Mode Expressions
- •Performing Simple Binary Arithmetic
- •Decomposing Expressions
- •Determining the Order of Operations
- •Performing Unary Operations
- •Using Assignment Operators
- •Why Mess with Logical Operations?
- •Using the Simple Logical Operators
- •Storing logical values
- •Using logical int variables
- •Be careful performing logical operations on floating-point variables
- •Expressing Binary Numbers
- •The decimal number system
- •Other number systems
- •The binary number system
- •Performing Bitwise Logical Operations
- •The single bit operators
- •Using the bitwise operators
- •A simple test
- •Do something logical with logical calculations
- •Controlling Program Flow with the Branch Commands
- •Executing Loops in a Program
- •Looping while a condition is true
- •Using the for loop
- •Avoiding the dreaded infinite loop
- •Applying special loop controls
- •Nesting Control Commands
- •Switching to a Different Subject?
- •Writing and Using a Function
- •Divide and conquer
- •Understanding the Details of Functions
- •Understanding simple functions
- •Understanding functions with arguments
- •Overloading Function Names
- •Defining Function Prototypes
- •Variable Storage Types
- •Including Include Files
- •Considering the Need for Arrays
- •Using an array
- •Initializing an array
- •Accessing too far into an array
- •Using arrays
- •Defining and using arrays of arrays
- •Using Arrays of Characters
- •Creating an array of characters
- •Creating a string of characters
- •Manipulating Strings with Character
- •String-ing Along Variables
- •Variable Size
- •Address Operators
- •Using Pointer Variables
- •Comparing pointers and houses
- •Using different types of pointers
- •Passing Pointers to Functions
- •Passing by value
- •Passing pointer values
- •Passing by reference
- •Limiting scope
- •Examining the scope problem
- •Providing a solution using the heap
- •Defining Operations on Pointer Variables
- •Re-examining arrays in light of pointer variables
- •Applying operators to the address of an array
- •Expanding pointer operations to a string
- •Justifying pointer-based string manipulation
- •Applying operators to pointer types other than char
- •Contrasting a pointer with an array
- •Declaring and Using Arrays of Pointers
- •Utilizing arrays of character strings
- •Identifying Types of Errors
- •Choosing the WRITE Technique for the Problem
- •Catching bug #1
- •Catching bug #2
- •Calling for the Debugger
- •Defining the debugger
- •Finding commonalities among us
- •Running a test program
- •Single-stepping through a program
- •Abstracting Microwave Ovens
- •Preparing functional nachos
- •Preparing object-oriented nachos
- •Classifying Microwave Ovens
- •Why Classify?
- •Introducing the Class
- •The Format of a Class
- •Accessing the Members of a Class
- •Activating Our Objects
- •Simulating real-world objects
- •Why bother with member functions?
- •Adding a Member Function
- •Creating a member function
- •Naming class members
- •Calling a Member Function
- •Accessing a member function
- •Accessing other members from a member function
- •Defining a Member Function in the Class
- •Keeping a Member Function After Class
- •Overloading Member Functions
- •Defining Arrays of and Pointers to Simple Things
- •Declaring Arrays of Objects
- •Declaring Pointers to Objects
- •Dereferencing an object pointer
- •Pointing toward arrow pointers
- •Passing Objects to Functions
- •Calling a function with an object value
- •Calling a function with an object pointer
- •Calling a function by using the reference operator
- •Returning to the Heap
- •Comparing Pointers to References
- •Linking Up with Linked Lists
- •Performing other operations on a linked list
- •Hooking up with a LinkedListData program
- •A Ray of Hope: A List of Containers Linked to the C++ Library
- •Protecting Members
- •Why you need protected members
- •Discovering how protected members work
- •Protecting the internal state of the class
- •Using a class with a limited interface
- •Creating Objects
- •Using Constructors
- •Why you need constructors
- •Making constructors work
- •Dissecting a Destructor
- •Why you need the destructor
- •Working with destructors
- •Outfitting Constructors with Arguments
- •Justifying constructors
- •Using a constructor
- •Defaulting Default Constructors
- •Constructing Class Members
- •Constructing a complex data member
- •Constructing a constant data member
- •Constructing the Order of Construction
- •Local objects construct in order
- •Static objects construct only once
- •Global objects construct in no particular order
- •Members construct in the order in which they are declared
- •Destructors destruct in the reverse order of the constructors
- •Copying an Object
- •Why you need the copy constructor
- •Using the copy constructor
- •The Automatic Copy Constructor
- •Creating Shallow Copies versus Deep Copies
- •Avoiding temporaries, permanently
- •Defining a Static Member
- •Why you need static members
- •Using static members
- •Referencing static data members
- •Uses for static data members
- •Declaring Static Member Functions
- •What Is This About, Anyway?
- •Do I Need My Inheritance?
- •How Does a Class Inherit?
- •Using a subclass
- •Constructing a subclass
- •Destructing a subclass
- •Having a HAS_A Relationship
- •Why You Need Polymorphism
- •How Polymorphism Works
- •When Is a Virtual Function Not?
- •Considering Virtual Considerations
- •Factoring
- •Implementing Abstract Classes
- •Describing the abstract class concept
- •Making an honest class out of an abstract class
- •Passing abstract classes
- •Factoring C++ Source Code
- •Defining a namespace
- •Implementing Student
- •Implementing an application
- •Project file
- •Creating a project file under Dev-C++
- •Comparing Operators with Functions
- •Inserting a New Operator
- •Overloading the Assignment Operator
- •Protecting the Escape Hatch
- •How Stream I/O Works
- •The fstream Subclasses
- •Reading Directly from a Stream
- •Using the strstream Subclasses
- •Manipulating Manipulators
- •Justifying a New Error Mechanism?
- •Examining the Exception Mechanism
- •What Kinds of Things Can I Throw?
- •Adding Virtual Inheritance
- •Voicing a Contrary Opinion
- •Generalizing a Function into a Template
- •Template Classes
- •Do I Really Need Template Classes?
- •Tips for Using Templates
- •The string Container
- •The list Containers
- •Iterators
- •Using Maps
- •Enabling All Warnings and Error Messages
- •Insisting on Clean Compiles
- •Limiting the Visibility
- •Avoid Overloading Operators
- •Heap Handling
- •Using Exceptions to Handle Errors
- •Avoiding Multiple Inheritance
- •Customize Editor Settings to Your Taste
- •Highlight Matching Braces/Parentheses
- •Enable Exception Handling
- •Include Debugging Information (Sometimes)
- •Create a Project File
- •Customize the Help Menu
- •Reset Breakpoints after Editing the File
- •Avoid Illegal Filenames
- •Include #include Files in Your Project
- •Executing the Profiler
- •System Requirements
- •Using the CD with Microsoft Windows
- •Using the CD with Linux
- •Development tools
- •Program source code
- •Index
Chapter 6: Creating Functions |
87 |
This is the same FunctionDemo() program, except that SquareDemo() accumulates the square of the values entered. The function square() returns the value of its one argument multiplied by itself. The change to the sumSequence() function is simple — rather than accumulate the value entered, the function now accumulates the result returned from square().
Functions with multiple arguments
Functions may have multiple arguments that are separated by commas. Thus, the following function returns the product of its two arguments:
int product(int arg1, int arg2)
{
return arg1 * arg2;
}
main() exposed
The “keyword” main() from our standard program template is nothing more than a function — albeit a function with strange arguments — but a function nonetheless.
When a program is built, C++ adds some boilerplate code that executes before your program ever starts (you can’t see this code without digging into the bowels of the C++ library functions). This code sets up the environment in which your program operates. For example, this boilerplate code opens the default input and output channels cin and cout.
After the environment has been established, the C++ boilerplate code calls the function main(), thereby beginning execution of your code. When your program finishes, it exits from main(). This enables the C++ boilerplate to clean up a few things before turning control over to the operating system that kills the program.
Overloading Function Names
C++ allows the programmer to assign the same name to two or more functions. This multiple use of names is known as overloading functions.
In general, two functions in a single program cannot share the same name. If they did, C++ would have no way to distinguish them. Note, however, that the name of the function includes the number and type of its arguments — but does not include its return argument. Thus the following are not the same functions:
88 Part II: Becoming a Functional C++ Programmer
void someFunction(void)
{
// ....perform some function
}
void someFunction(int n)
{
// ...perform some different function
}
void someFunction(double d)
{
// ...perform some very different function
}
void someFunction(int n1, int n2)
{
// ....do something different yet
}
C++ still knows that the functions someFunction(void), someFunction(int), someFunction(double), and someFunction(int, int) are not the same. Like so many things that deal with computers, this has an analogy in the human world.
void as an argument type is optional. sumFunction(void) and sumFunction() are the same function. A function has a shorthand name, such as someFunction(), in same way that I have the shorthand name Stephen (actually, my nickname is Randy, but work with me on this one). If there aren’t any other Stephens around, people can talk about Stephen behind his back. If, however, there are other Stephens, no matter how hand some they might be, people have to use their full names — in my case, Stephen Davis. As long as we use the entire name, no one gets confused — however many Stephens might be milling around. Similarly, the full name for one of the someFunctions() is someFunction(int). As long as this full name is unique, no confusion occurs.
The analogies between the computer world (wherever that is) and the human world are hardly surprising because humans build computers. (I wonder . . .
if dogs had built computers, would the standard unit of memory be a gnaw instead of a byte? Would requests group in packs instead of queues?)
Here’s a typical application that uses overloaded functions with unique full names:
int intVariable1, intVariable2; // equivalent to // int Variable1; // int Variable2;
double doubleVariable;
//functions are distinguished by the type of
//the argument passed
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Chapter 6: Creating Functions |
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someFunction(); |
// calls someFunction(void) |
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someFunction(intVariable1); |
// calls someFunction(int) |
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someFunction(doubleVariable); // calls someFunction(double) |
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someFunction(intVariable1, intVariable2); // calls |
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// someFunction(int, int) |
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// this works for constants as well |
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someFunction(1); |
// calls someFunction(int) |
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someFunction(1.0); |
// calls someFunction(double) |
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someFunction(1, 2); |
// calls someFunction(int, int) |
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In each case, the type of the arguments matches the full name of the three functions.
The return type is not part of the extended name (which is also known as the function signature) of the function. The following two functions have the same name — so they can’t be part of the same program:
int someFunction(int n); |
// |
full name of the function |
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// |
is someFunction(int) |
double someFunction(int n); // |
same name |
You’re allowed to mix variable types as long as the source variable type is more restrictive than the target type. Thus an int can be promoted to a double. The following is acceptable:
int someFunction(int n);
double d = someFunction(10); // promote returned value
The int returned by someFunction() is promoted into a double. Thus the following would be confusing:
int someFunction(int n); double someFunction(int n);
double d = someFunction(10);// promote returned int?
// or use returned double as is
Here C++ does not know whether to use the value returned from the double version of someFunction() or promote the value returned from int version.
Defining Function Prototypes
The programmer may provide the remainder of a C++ source file, or module, the extended name (the name and functions) during the definition of the function.
90 |
Part II: Becoming a Functional C++ Programmer |
The target functions sumSequence() and square() — appearing earlier in this chapter — are both defined in the code that appears before the actual call. This doesn’t have to be the case: A function may be defined anywhere in the module. (A module is another name for a C++ source file.)
However, something has to tell the calling function the full name of the func tion to be called. Consider the following code snippet:
int main(int nNumberofArgs, char* pszArgs[])
{
someFunc(1, 2);
}
int someFunc(double arg1, int arg2)
{
// ...do something
}
main() doesn’t know the full name of the function someFunc() at the time of the call. It may surmise from the arguments that the name is someFunc(int, int) and that its return type is void — but as you can see, this is incorrect.
I know, I know — C++ could be less lazy and look ahead to determine the full name of someFunc()s on its own, but it doesn’t. It’s like my crummy car; it gets me there, and I’ve learned to live with it.
What is needed is some way to inform main() of the full name of someFunc() before it is used. This is handled by what we call a function prototype.
A prototype declaration appears the same as a function with no body. In use, a prototype declaration looks like this:
int someFunc(double, int);
int main(int nNumberofArgs, char* pszArgs[])
{
someFunc(1, 2);
}
int someFunc(double arg1, int arg2)
{
// ...do something
}
The prototype declaration tells the world (at least that part of the world after the declaration) that the extended name for someFunc() is someFunction(double, int). The call in main() now knows to cast the 1 to a double before making the call. In addition, main() knows that the value returned by someFunc() is an int.