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The arguments to a macro should not include preprocessor directives such as {{\#define}}, {{\#ifdef}}, and {{\#include}}.  Doing so is [undefined behavior|BB. Definitions#undefined behavior] according to section 6.10.3, paragraph 11 of the C99 standard \[[ISO/IEC 9899:1999|AA. References#ISOBibliography#ISO/IEC 9899-1999]\] (see also [undefined behavior 87 | CC. Undefined Behavior#ub_87] of Annex J):
<blockquote><p>The sequence of preprocessing tokens bounded by the outside-most matching parentheses forms the list of arguments for the function-like macro.&nbsp; The individual arguments within the list are separated by comma preprocessing tokens, but comma preprocessing tokens between matching inner parentheses do not separate arguments.&nbsp; <strong>If there are sequences of preprocessing tokens within the list of arguments that would otherwise act as preprocessing directives, the behavior is undefined.</strong></p></blockquote>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.&nbsp;  For example, standard library functions such as {{memcpy()}}, {{printf()}}, and {{assert()}} may be implemented as macros.

\[[GCC Bugs|http://gcc.gnu.org/bugs.html#nonbugs_c]\] "Non-bugs"
\[[ISO/IEC 9899:1999|AA. References#ISOBibliography#ISO/IEC 9899-1999]\] Section 6.10.3.1, "Argument substitution," paragraph 11