Programming Concepts and Vocabulary for Windows

	Chapter 18 - Complete I/O in C++
	Visual C++ 6: The Complete Reference
	Chris H. Pappas and William H. Murray, III

Copyright 1998 The McGraw-Hill Companies

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	Using enum Types in C++

	User-defined enumerated types behave differently in C++ than their C counterparts. For example, C enum types are compatible with the type int. This means they can be cross-assigned with no complaints from the compiler. However, in C++ the two types are incompatible.

	Another difference between C and C++ enumerated types involves the syntax shorthand when you define C++ enum variables. The following example program highlights the enumerated type differences between the two languages:

	// //  enum.cpp //  C++ program demonstrates how to use enumerated types and //  how C++ enumerated types differ from C enumerated types //  Copyright (c) Chris H. Pappas and William H. Murray, 1998 // #include <iostream.h> typedef enum boolean { FALSE, TRUE }; void main(void) { // enum boolean bflag = 0; legal C, but illegal C++ statement   boolean bcontinue, bflag = FALSE;   bcontinue = (boolean)1;   bflag = bcontinue; }

	This code starts by defining the enumerated type boolean, which is a standard type in several other high-level languages. Because of the ordering of the definition —FALSE, then TRUE—the compiler assigns a zero to FALSE and a 1 to TRUE. This is perfect for their logical use in a program.

	The statement, commented out in the main( ) program, represents a legal C statement. Remember, when you define enumerated variables in C, such as bflag, you must use the enum keyword with the enumerated type’s tag field—in this case, boolean. Since C enum types are compatible with int types, it is also legal to initialize a variable with an integer value. This statement would not get past the C++ compiler. The second statement in main( ) shows the legal C++ counterpart.

	The final two statements in the program show how to use enumerated types. Notice that in C++, an explicit cast (boolean), is needed to convert the 1 to a boolean-compatible type.

	User-defined types cannot be directly input from or output to a file, as you may recall. Either they must go through a conversion routine or you can custom overload the >> and << operators, as discussed in Chapter 12.

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