Practical C Programming, 3rd Edition

2017-07-07 02:10:07

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As you've seen, C++ allows you to specify a number of qualifiers for variable declarations. Qualifiers may be thought of as adjectives that describe the type that follows . Table 5-2 summarizes the various qualifiers; they are explained in detail in the following sections.

Table 5-2. Qualifiers and simple types

Special	Constant	Storage class	Size	Sign	Type
volatile	const	register	long	signed	int
<blank>	<blank>	static	short	unsigned	float
		extern	double	<blank>	char
		auto	<blank>		wchar_t
		<blank>			<blank>

5.10.1 Special

The volatile keyword is used for specialized programming such as I/O drivers and shared memory applications. It is an advanced modifier whose use is far beyond the scope of this book.

volatile: Indicates a special variable whose value may change at any time
<blank>: Normal variable

5.10.2 Constant

The const keyword indicates a value that cannot be changed.

const: Indicates that this is a declaration of constant data
<blank>: Normal variable

5.10.3 Storage Class

The class of a variable is discussed in detail in Chapter 9. A brief description of the various classes follows:

register: This indicates a frequently used variable that should be kept in a machine register. See Chapter 17.
static: The meaning of this word depends on the context. This keyword is described in Chapter 9 and Chapter 23.
extern: The variable is defined in another file. See Chapter 23 for more information.
auto: A variable allocated from the stack. This keyword is hardly ever used.
<blank>: Indicates that the default storage class is selected. For variables declared outside a function, this makes the variable global. Variables inside a function are declared auto .

5.10.4 Size

The size qualifier allows you to select the most efficient size for the variable.

long: Indicates a larger than normal number.
short: Indicates a smaller than normal integer.
double: Indicates a double-size floating-point number.
<blank>: Indicates a normal-size number.

5.10.5 Sign

Numbers can be signed or unsigned . This qualifier applies only to char and int types. Floating-point numbers are always signed. The default is signed for int and undefined for characters .

5.10.6 Type

This specifies the type of the variable. Simple types include:

int: Integer.
float: Floating-point number.
char: Single character, but can also be used for a very short integer.
wchar_t: Single wide character. Can also be used for a short integer, but most people don't because the other integer types are more appropriate to use.