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POC++ extern: pointer vs. reference
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copied!<p>I have three classes: <code>ConsoleInputStream</code>, <code>ConsoleOutputStream</code>, <code>ConsoleErrorStream</code>. All of them are derived from <code>Stream</code>.</p> <p>Each stream has virtual functions <code>read</code> and <code>write</code>; as you guess, when user tries to use <code>ConsoleInputStream</code>'s <code>write</code> member function, it throws an error. Same happens when user tries to use <code>ConsoleOutputStream</code>'s <code>write</code> function.</p> <p>Now it's time to show the code.</p> <pre><code>// STREAM.HPP namespace streamlib { extern ConsoleInputStream stdin_default; extern ConsoleOutputStream stdout_default; extern ConsoleErrorStream stderr_default; extern Stream& stdin; extern Stream& stdout; extern Stream& stderr; } // namespace streamlib // STREAM.CPP namespace streamlib { ConsoleInputStream stdin_default; ConsoleOutputStream stdout_default; ConsoleErrorStream stderr_default; Stream& stdin = stdin_default; Stream& stdout = stdout_default; Stream& stderr = stderr_default; } // namespace streamlib // MAIN.CPP int main() { streamlib::stdout = streamlib::stdin; streamlib::stdout.write(); // Still working, but should have thrown error! } </code></pre> <p>However, everything works perfectly well when I define <code>stdin</code>, <code>stdout</code> and <code>stderr</code> as pointers instead of references, i.e. error is thrown as expected. But I don't want to allocate/free memory and use <code>-></code> operator where I could (could I?) use plain dot operator.</p> <p>The real situation is of course even more intricated: I also have some other types derived from <code>Stream</code> and just want to be able to quickly overload <code>stdin</code>, <code>stdout</code>, <code>stderr</code> streams with different kind of streams. Is it possible to do it with references?</p> <p>Thanks in advance!</p>

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