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[wwwdocs] Document C++ null pointer constant changes in gcc-7/porting_to.html
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Jason Merrill <jason at redhat dot com>, Marek Polacek <polacek at redhat dot com>
- Date: Fri, 7 Apr 2017 10:25:21 +0100
- Subject: [wwwdocs] Document C++ null pointer constant changes in gcc-7/porting_to.html
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This issue caused a lot of build failures during the GCC mass rebuilds
for Fedora, but isn't in the porting to guide yet.
Is this accurate and clear enough for casual readers?
Index: htdocs/gcc-7/porting_to.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/porting_to.html,v
retrieving revision 1.13
diff -u -r1.13 porting_to.html
--- htdocs/gcc-7/porting_to.html 6 Apr 2017 17:12:16 -0000 1.13
+++ htdocs/gcc-7/porting_to.html 7 Apr 2017 09:25:06 -0000
@@ -118,6 +118,39 @@
with GCC 7 and some are compiled with older releases.
</p>
+<h3 id="null-pointer-constants">Null pointer constants</h3>
+
+<p>
+When compiling as C++11 or later, GCC 7 follows the revised definition of a
+<em>null pointer constant</em>. This means conversions to pointers from other
+types of constant (such as character literals and boolean literals) will now
+be rejected.
+</p>
+
+<pre><code>void* f() {
+ char* p = '\0';
+ return false;
+}
+</code></pre>
+
+ <blockquote><pre>
+<span class="boldred">error:</span> invalid conversion from <b>'char'</b> to <b>'char*'</b> [<span class="boldred">-fpermissive</span>]
+ char* p = <span class="boldred">'\0'</span>;
+ <span class="boldred">^~~~</span>
+<span class="boldred">error:</span> cannot convert <b>'bool'</b> to <b>'void*'</b> in return
+ return <span class="boldred">false</span>;
+ <span class="boldred">^~~~~</span>
+</pre></blockquote>
+
+<p>
+Such code should be fixed to use a valid null pointer constant such as
+<code>0</code> or <code>nullptr</code>. Care should be taken when fixing
+invalid uses of <code>'\0'</code> as a pointer, as it may not be clear whether
+the intention was to create a null pointer (<code>p = 0;</code>), to create an
+empty string (<code>p = "";</code>), or to write a null terminator to the
+string (<code>*p = '\0';</code>).
+</p>
+
<h3 id="header-dep-changes">Header dependency changes</h3>
<p>