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     <td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">The
       Macro Expansion Process</font></b></font></td>
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 <p>The macro expansion process described here was initially developed by <a href="mailto:pmenso57@attbi.com">Paul
   Mensonides</a> and is implemented in <tt>Wave</tt>. It is much more understandable
   as the description of the desired macro expansion algorithm provided in the
   C++ Standard <a href="references.html#iso_cpp">[1]</a>.</p>
 <p>Macro replacement proceeds left-to-right. </p>
 <p>If, during scanning (or rescanning) an identifier is found, it is looked up
   in the symbol table. If the identifier is not found in the symbol table, it
   is not a macro and scanning continues.</p>
 <p>If the identifier is found, the value of a flag associated with the identifier
   is used to determine if the identifier is available for expansion. If it is
   not, the specific token (i.e. the specific instance of the identifier) is marked
   as disabled and is not expanded. If the identifier is available for expansion,
   the value of a different flag associated with the identifier in the symbol table
   is used to determine if the identifier is an object-like or function-like macro.
   If it is an object-like macro, it is expanded. If it is a function-like macro,
   it is only expanded if the next token is an left parenthesis.<br>
   An identifier is available for expansion if it is not marked as disabled and
   if the the value of the flag associated with the identifier is not set, which
   is used to determine if the identifier is available for expansion.</p>
 <p>(If a macro is an object-like macro, skip past the next two paragraphs.)</p>
 <p>If a macro to be expanded is a function-like macro, it must have the exact
   number of actual arguments as the number of formal parameters required by the
   definition of the macro. Each argument is recursively scanned and expanded.
   Each parameter name found in the replacement list is replaced by the expanded
   actual argument after leading and trailing whitespace and all placeholder tokens
   are removed unless the parameter name immediately follows the stringizing operator
   (<tt>'#'</tt>) or is adjacent to the token-pasting operator (<tt>'##'</tt>).</p>
 <p>If the parameter name immediately follows the stringizing operator (<tt>'#'</tt>),
   a stringized version of the unexpanded actual argument is inserted. If the parameter
   name is adjacent to the token-pasting operator (<tt>'##'</tt>), the unexpanded
   actual argument is inserted after all placeholder tokens are removed.</p>
 <p>All concatenation takes place in the replacement list. (If a single concatenation
   yields multiple tokens, the behavior is undefined. Moreover, <tt>Wave</tt> in
   normal C++98 and C99 modes issues an error, if more then one token is produced
   as the result of the concatenation. In C++0x mode <tt>Wave</tt> treats token-pasting
   of unrelated tokens as well defined and inserts the reparsed string representation
   of the concatenated tokens into the replacement list.).</p>
 <p>The flag in the symbol table entry associated with the name of the macro being
   expanded is set to indicate the that the macro is not available for expansion.</p>
 <p>The replacement list is rescanned for further macro expansion. All leading
   and trailing whitespace tokens in the replacement list are removed (the placeholder
   tokens are left intact). </p>
 <p>After rescanning completes, the flag in the symbol table entry associated with
   the name of macro being expanded is cleared to indicate that the macro is again
   available for expansion, and the sequence of tokens that constitutes the rescanned
   replacement list is returned to the point of invocation of the macro.</p>
 <p>If this sequence of tokens is empty, it is replaced by a placeholder token.
   If a placeholder is found during scanning (or rescanning) it is ignored. (Also,
   if the only thing separating a parameter from the stringizing operator or token-pasting
   operator is placeholder, it is also ignored in that context.)</p>
 <p>This sequence of tokens is inserted at the original point that the macro was
   invoked, and scanning continues starting with the last token of the newly inserted
   sequence of tokens. I.e. scanning looks back a single token (possibly a placeholder
   token) and continues.<br>
 </p>
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 <p class="copyright">Copyright &copy; 2003-2010 Hartmut Kaiser<br>
   <br>
 <font size="2">Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) </font> </p>
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 <!-- #BeginDate format:fcAm1m -->Saturday, February 25, 2006  15:46<!-- #EndDate -->
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
	<html>
	<head>
	<title>The Macro Expansion Process</title>
	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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	</head>

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	<tr>
	<td width="21"> <h1></h1></td>
	<td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">The
	Macro Expansion Process</font></b></font></td>
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	<p>The macro expansion process described here was initially developed by <a href="mailto:pmenso57@attbi.com">Paul
	Mensonides</a> and is implemented in <tt>Wave</tt>. It is much more understandable
	as the description of the desired macro expansion algorithm provided in the
	C++ Standard <a href="references.html#iso_cpp">[1]</a>.</p>
	<p>Macro replacement proceeds left-to-right. </p>
	<p>If, during scanning (or rescanning) an identifier is found, it is looked up
	in the symbol table. If the identifier is not found in the symbol table, it
	is not a macro and scanning continues.</p>
	<p>If the identifier is found, the value of a flag associated with the identifier
	is used to determine if the identifier is available for expansion. If it is
	not, the specific token (i.e. the specific instance of the identifier) is marked
	as disabled and is not expanded. If the identifier is available for expansion,
	the value of a different flag associated with the identifier in the symbol table
	is used to determine if the identifier is an object-like or function-like macro.
	If it is an object-like macro, it is expanded. If it is a function-like macro,
	it is only expanded if the next token is an left parenthesis.<br>
	An identifier is available for expansion if it is not marked as disabled and
	if the the value of the flag associated with the identifier is not set, which
	is used to determine if the identifier is available for expansion.</p>
	<p>(If a macro is an object-like macro, skip past the next two paragraphs.)</p>
	<p>If a macro to be expanded is a function-like macro, it must have the exact
	number of actual arguments as the number of formal parameters required by the
	definition of the macro. Each argument is recursively scanned and expanded.
	Each parameter name found in the replacement list is replaced by the expanded
	actual argument after leading and trailing whitespace and all placeholder tokens
	are removed unless the parameter name immediately follows the stringizing operator
	(<tt>'#'</tt>) or is adjacent to the token-pasting operator (<tt>'##'</tt>).</p>
	<p>If the parameter name immediately follows the stringizing operator (<tt>'#'</tt>),
	a stringized version of the unexpanded actual argument is inserted. If the parameter
	name is adjacent to the token-pasting operator (<tt>'##'</tt>), the unexpanded
	actual argument is inserted after all placeholder tokens are removed.</p>
	<p>All concatenation takes place in the replacement list. (If a single concatenation
	yields multiple tokens, the behavior is undefined. Moreover, <tt>Wave</tt> in
	normal C++98 and C99 modes issues an error, if more then one token is produced
	as the result of the concatenation. In C++0x mode <tt>Wave</tt> treats token-pasting
	of unrelated tokens as well defined and inserts the reparsed string representation
	of the concatenated tokens into the replacement list.).</p>
	<p>The flag in the symbol table entry associated with the name of the macro being
	expanded is set to indicate the that the macro is not available for expansion.</p>
	<p>The replacement list is rescanned for further macro expansion. All leading
	and trailing whitespace tokens in the replacement list are removed (the placeholder
	tokens are left intact). </p>
	<p>After rescanning completes, the flag in the symbol table entry associated with
	the name of macro being expanded is cleared to indicate that the macro is again
	available for expansion, and the sequence of tokens that constitutes the rescanned
	replacement list is returned to the point of invocation of the macro.</p>
	<p>If this sequence of tokens is empty, it is replaced by a placeholder token.
	If a placeholder is found during scanning (or rescanning) it is ignored. (Also,
	if the only thing separating a parameter from the stringizing operator or token-pasting
	operator is placeholder, it is also ignored in that context.)</p>
	<p>This sequence of tokens is inserted at the original point that the macro was
	invoked, and scanning continues starting with the last token of the newly inserted
	sequence of tokens. I.e. scanning looks back a single token (possibly a placeholder
	token) and continues.<br>
	</p>
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	<hr size="1">
	<p class="copyright">Copyright © 2003-2010 Hartmut Kaiser<br>
	<br>
	<font size="2">Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) </font> </p>
	<span class="updated"></span>
	<p class="copyright"><span class="updated">Last updated:
	<!-- #BeginDate format:fcAm1m -->Sunday, May 15, 2005 12:23<!-- #EndDate -->
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	<!-- #BeginDate format:fcAm1m -->Saturday, February 25, 2006 15:46<!-- #EndDate -->