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This chapter is from the book

Using Type Definitions

When a C++ program contains a lot of variables, it can be repetitious and error-prone to keep writing unsigned short int for each one. A shortcut for an existing type can be created with the keyword typedef, which stands for type definition.

A typedef requires typedef followed by the existing type and its new name. Here's an example:

typedef unsigned short USHORT

This statement creates a type definition named USHORT that can be used anywhere in a program in place of unsigned short. The NewRectangle program in Listing 3.3 is a rewrite of Rectangle that uses this type definition.

Listing 3.3. The Full Text of NewRectangle.cpp

 1: #include <iostream>
 2:
 3: int main()
 4: {
 5:     // create a type definition
 6:     typedef unsigned short USHORT;
 7:
 8:     // set up width and length
 9:     USHORT width = 5;
10:     USHORT length = 10;
11:
12:     // create an unsigned short initialized with the
13:     // result of multiplying width by length
14:     USHORT area = width * length;
15:
16:     std::cout << "Width: " << width << "\n";
17:     std::cout << "Length: " << length << "\n";
18:     std::cout << "Area: " << area << "\n";
19:     return 0;
20: }

This program has the same output as Rectangle: the values of width (5), length (10), and area (50).

On line 6, the USHORT typedef is created as a shortcut for unsigned short. A type definition substitutes the underlying definition unsigned short wherever the shortcut USHORT is used.

During Hour , "Creating Basic Classes," you learn how to create new types in C++. This is a different from creating type definitions.

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