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POHow to return an fstream (C++0x)
 

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    <p>I think I'll get right into it and start with the code:</p> <pre><code>#include &lt;iostream&gt; #include &lt;fstream&gt; #include &lt;string&gt; class test : public std::ofstream { public: test(const std::string&amp; filename) { this-&gt;open(gen_filename(filename)); }; test(const test&amp;) = delete; //test(test&amp;&amp; old) = default; // Didn't compile test(test&amp;&amp; old) {}; private: std::string gen_filename(const std::string&amp; filename) { return filename + ".tmp"; } }; int main() { auto os = test("testfile"); os &lt;&lt; "Test1\n"; os &lt;&lt; "Test2\n"; } </code></pre> <p>Basically, I need to return an ofstream. Of course you can't copy an ofstream, so I fiddled around with the code in the class test, and I got the above to compile and work as you would expect (on gcc 4.5).</p> <p>But I have a bad feeling this is just due to my compiler doing "Return Value Optimization" (RTO) on "auto os = test()". Indeed, if modify to the following:</p> <pre><code>int main() { auto os = test("testfile"); os &lt;&lt; "Test1\n"; auto os2 = std::move(os); os2 &lt;&lt; "Test2\n"; } </code></pre> <p>I no longer get both Test1 and Test2 in the output.</p> <p>The thing is, the class "test" isn't copyable, so there's no chance of the ofstream being duplicated. I just want to be able to return it from a function. And I seem to be able to do that with GCC.</p> <p>I'd rather not have dereference smart pointers to a heap allocated ofstream, or reopen the file, as it currently works without doing those things. I just have a feeling I'm being a little "non-standard" in my approach, so a standard way of doing what I've described would be great.</p>
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