<p>One of the vagaries of my development system (Codegear C++Builder) is that some of the auto-generated headers insist on having... </p>

<pre><code>using namespace xyzzy
</code></pre>

<p>...statements in them, which impact on my code when I least want or expect it.</p>

<p>Is there a way I can somehow cancel/override a previous "using" statement to avoid this.</p>

<p>Maybe...</p>

<pre><code>unusing namespace xyzzy;
</code></pre>

No you can't
unuse
a namespace. The only thing you can do is putting the
```
using namespace
```
-statement a block to limit it's scope.
Example:
```
```
{
    using namespace xyzzy;

} // stop using namespace xyzzy here
```
```
Maybe you can change the template which is used of your auto-generated headers.