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    CWG Issue 179</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="179"></A><H4>179.
  
Function pointers and subtraction
</H4>
<B>Section: </B>7.6.6&#160; [<A href="https://wg21.link/expr.add">expr.add</A>]
 &#160;&#160;&#160;

 <B>Status: </B>TC1
 &#160;&#160;&#160;

 <B>Submitter: </B>Mike Miller
 &#160;&#160;&#160;

 <B>Date: </B>Nov 1999<BR>



<P>7.6.6 [<A href="https://wg21.link/expr.add#8">expr.add</A>] paragraph 8
explicitly
allows subtraction of two pointers to functions:</P>

<BLOCKQUOTE>
If two pointers point to the same object <B>or function</B>... and the
two pointers are subtracted...
</BLOCKQUOTE>

However, 7.6.6 [<A href="https://wg21.link/expr.add#2">expr.add</A>] paragraph 2

requires that two pointers that are subtracted be pointers to an
<B>object</B> type; function pointers are not allowed.

<P>Being able to subtract two pointers to functions doesn't seem
terribly useful, especially considering that subtracting two pointers
to different functions appears to produce undefined behavior rather
than simply a non-zero result, according to paragraph 6:</P>

<BLOCKQUOTE>
Unless both pointers point to elements of the same array object, or
one past the last element of the array object, the behavior is
undefined.
</BLOCKQUOTE>

<P><B>Proposed resolution (10/00):</B></P>

<P>Remove the words <B>or function</B>
from paragraph 8.</P>
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