C Pocket Reference

Name

#define

Synopsis

The #define directive is used to define macros.

Syntax:

define name[(parameter_list)]  [replacement_text]

The preprocessor replaces each occurrence of name or name(parameter_list) in the subsequent source code with replacement_text.

Examples:

#define  BUF_SIZE  512        // Symbolic constant
#define  MAX(a,b)  ((a) > (b) ? (a) : (b))

These directives define the macros BUF_SIZE and MAX. If the replacement text is a constant expression, the macro is also called a symbolic constant . Macros can also be nested; a macro, once defined, can be used in another macro definition.

In the previous example, the parentheses are necessary in order for the substitution to be performed correctly when MAX is used in an expression, or when complex expressions replace the parameters a and b. For example, the preprocessor replaces the macro invocation:

result = 2 * MAX( x, y & 0xFF );

with:

result = 2 * ( (x) > (y & 0xFF) ? (x) : (y & 0xFF) );