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The sequence of preprocessing tokens bounded by the outside-most matching parentheses forms the list of arguments for the function-like macro. The individual arguments within the list are separated by comma preprocessing tokens, but comma preprocessing tokens between matching inner parentheses do not separate arguments. If there are sequences of preprocessing tokens within the list of arguments that would otherwise act as preprocessing directives, the behavior is undefined.

(See also undefined behavior 93behavior 93 of Annex J.)

The scope of this rule includes using preprocessor directives in arguments to a function where it is unknown whether or not the function is implemented using a macro. For example, standard library functions, such as memcpy(), printf(), and assert(), may be implemented as macros.

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