C/C++ Programmer's Guide (G06.25+)

Preprocessor Directives and Macros
HP C/C++ Programmer’s Guide for NonStop Servers—429301-002
12-2
#define
#define
The #define directive defines a macro, providing it with a name (an identifier) and the
replacement list that the name represents. The macro can be either object-like or
function-like, depending on how you define it.
object-like-name
specifies the name of an object-like macro; it must be a valid identifier.
function-like-name
specifies the name and parameters (if any) of a function-like macro. The parameter
list is a parenthesized, comma-separated list of zero or more identifiers. Note that
there can be no white space between the macro identifier and the opening
parenthesis of the parameter list.
replacement-list
is the text that the preprocessor substitutes for the macro name when you invoke
the macro later in the translation unit. The replacement-list must be valid in
the context where you invoke it, not where you define it.
If the macro is function-like and has defined parameters, the preprocessor
substitutes each instance of a parameter identifier in the replacement-list with
its corresponding argument specified in the macro invocation. The second example
illustrates parameter substitution.
newline
is the newline character that terminates the directive line.
Usage Guidelines
•
If you need more than one physical line to complete the definition of a macro, place
a backslash (\) at the end of all but the last line of the definition. The backslashes
cause these physical lines to be concatenated into a single logical line.
•
The #ifdef and #ifndef directives enable you to test whether an identifier is
currently defined as a macro name.
•
The #undef directive enables you to remove a macro definition so that the
identifier is no longer defined as a macro name.
#define { object-like-name } replacement-list newline
{ function-like-name }
object-like-name:
identifier
function-like-name:
identifier( [parameter-list] )