This chapter is from the book
This chapter is from the book
This chapter is from the book
typedef
It can become tedious, repetitious, and, most important, error-prone to keep writing unsigned short int. C++ enables you to create an alias for this phrase by using the keyword typedef, which stands for type definition.
In effect, you are creating a synonym, and it is important to distinguish this from creating a new type (which you will do on Day 6, "Object-Oriented Programming"). typedef is used by writing the keyword typedef, followed by the existing type, then the new name, and ending with a semicolon. For example,
typedef unsigned short int USHORT;
creates the new name USHORT that you can use anywhere you might have written unsigned short int. Listing 3.3 is a replay of Listing 3.2, using the type definition USHORT rather than unsigned short int.
Listing 3.3 A Demonstration of typedef
0: // *****************
1: // Demonstrates typedef keyword
2: #include <iostream>
3:
4: typedef unsigned short int USHORT; //typedef defined
5:
6: int main()
7: {
8:
9: using std::cout;
10: using std::endl;
11:
12: USHORT Width = 5;
13: USHORT Length;
14: Length = 10;
15: USHORT Area = Width * Length;
16: cout << "Width:" << Width << "\n";
17: cout << "Length: " << Length << endl;
18: cout << "Area: " << Area <<endl;
19: return 0;
20: }
Output
Width:5 Length: 10 Area: 50
NOTE
* indicates multiplication.
Analysis On line 4, USHORT is typedefined (some programmers say "typedef'ed") as a synonym for unsigned short int. The program is very much like Listing 3.2, and the output is the same.