HP aC++/HP C A.06.20 Programmer's Guide

The macro name is then replaced by the list of tokens wherever it appears in the source

file (except inside of a string, character constant, or comment). A macro definition

remains in force until it is undefined through the use of the #undef directive or until

the end of the compilation unit.

The replacement-list must fit on one line. If the line becomes too long, it can be

broken up into several lines provided that all lines but the last are terminated by a

backslash (\) character. The following is an example:

#define mac very very long\

replacement string

The \ must be the last character on the line. You cannot add any spaces or comments

after it.

Macros can be redefined without an intervening #undef directive. Any parameter

used must agree in number and spelling with the original definition, and the

replacement lists must be identical. All white space within the replacement-list is treated

as a single blank space regardless of the number of white-space characters you use.

For example, the following #define directives are equivalent:

#define foo x + y

The replacement-list may be empty. If the token list is not provided, the macro

name is replaced with no characters.

Macros with Parameters

You can create macros that have parameters. The syntax of the #define directive that

includes formal parameters is as follows:

#define identifier( [identifier-list] ) [replacement-list]

The macro name is identifier. The formal parameters are provided by the

identifier-list enclosed in parentheses. The open parenthesis ( ‘(’ ) must

immediately follow the identifier with no intervening white space. If there is a space

between the identifier and the parenthesis, the macro is defined as if it were the first

form and the replacement-list begins with the ( character.

The formal parameters to the macro are separated with commas. They may or may not

appear in the replacement-list. When the macro is invoked, the actual arguments

are placed in a parenthesized list following the macro name. Commas enclosed in

additional matching pairs of parentheses do not separate arguments but are themselves

components of arguments.

The actual arguments replace the formal parameters in the token string when the macro

is invoked.

156 Preprocessing Directives