Re: [wwwdocs] Document C++ null pointer constant changes in gcc-7/porting_to.html

[Marek Polacek <polacek at redhat dot com>]

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