May 2003
Intermediate to advanced
808 pages
32h 24m
English
defined operator — Tests whether a macro is defined
defined(identifier) definedidentifier
The unary operator defined(
identifier ) (also written as defined
identifier, without the parentheses)
evaluates to 1 if
identifier is a known macro name at the
point of the defined operator, or
0 if it is not known. The operator
is evaluated only in the argument to an #if or #elif directive.
The behavior is undefined if the defined operator is used in any other way,
or if the token defined results
from macro expansion.