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POC++ Stringstream - copying with rd_buf changes const object
 

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  1. POC++ Stringstream - copying with rd_buf changes const object
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    <p>Given one stringstream object, I would like to copy it to another. According to :</p> <p><a href="https://stackoverflow.com/questions/3442520/how-copy-from-one-stringstream-object-to-another-in-c">how copy from one stringstream object to another in C++?</a></p> <p>(among others), the proper way to do this is to use the <code>rdbuf()</code> member. However, this seems to cause issues, particularly if the stringstream is const.</p> <p>For example:</p> <pre><code>void DoSomething(stringstream &amp; ss) { stringstream sstmp; cout &lt;&lt; "pos 1: " &lt;&lt; ss.tellg() &lt;&lt; "\n"; sstmp &lt;&lt; ss.rdbuf(); cout &lt;&lt; "pos 2: " &lt;&lt; ss.tellg() &lt;&lt; "\n"; // sstmp.rdbuf()-&gt;pubseekpos(0, ios_base::in | ios_base::out); cout &lt;&lt; "String: " &lt;&lt; sstmp.str() &lt;&lt; "\n"; } int main(void) { stringstream ss; ss &lt;&lt; "Hello"; DoSomething(ss); DoSomething(ss); return 0; } </code></pre> <p>The output is</p> <pre><code>pos 1: 0 pos 2: 5 String: Hello pos 1: 5 pos 2: 5 String: </code></pre> <p>The first call to <code>DoSomething()</code> changed the internal pointer, and seems to do so even if the <code>stringstream</code> is const (left out here as even <code>tellg()</code> is not const). The way to remedy this is with <code>seekg()</code>, but that can't be called on const streams. I attempted another way (commented out in the code) but without success.</p> <p>So what can be done to either:</p> <ol> <li><p>Copy a (const) <code>stringstream</code> without really changing it, or</p></li> <li><p>reset the position on a const object?</p></li> </ol> <p>Note: Compiled using gcc 4.8.1 on Arch Linux</p>
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    1. COLosing the `tellg()` calls and adding a call to `ss.rdbuf()->pubseekoff(0, std::ios_base::beg, std::ios_base::in);` will likely get what you want, but I'm not sure it will drive home what is the real question for me; why. Someone with deeper understanding of the stream lib will have to step in. Great question, and +1 for doing the initial homework on prospective answers.
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