| Message ID | 20170407092521.GA3733@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Fri, Apr 07, 2017 at 10:25:21AM +0100, Jonathan Wakely wrote: > 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? Looks fine to me. > 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> Marek
On 04/07/2017 03:25 AM, Jonathan Wakely wrote: > 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> Nit pick: s/will now be rejected/are now rejected/ since "now" means we are describing GCC's current behavior, not future behavior. :-) -Sandra
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>