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PO"Roll-Back" or Undo Any Manipulators Applied To A Stream Without Knowing What The Manipulators Were
 

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  1. PO"Roll-Back" or Undo Any Manipulators Applied To A Stream Without Knowing What The Manipulators Were
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    <p>If I apply an arbitrary number of manipulators to a stream, is there a way to undo the application of those manipulators in a generic way?</p> <p>For example, consider the following:</p> <pre><code>#include &lt;iostream&gt; #include &lt;iomanip&gt; using namespace std; int main() { cout &lt;&lt; "Hello" &lt;&lt; hex &lt;&lt; 42 &lt;&lt; "\n"; // now i want to "roll-back" cout to whatever state it was in // before the code above, *without* having to know // what modifiers I added to it // ... MAGIC HAPPENS! ... cout &lt;&lt; "This should not be in hex: " &lt;&lt; 42 &lt;&lt; "\n"; } </code></pre> <p>Suppose I want to add code at <code>MAGIC HAPPENS</code> that will revert the state of the stream manipulators to whatever it was before I did <code>cout &lt;&lt; hex</code>. <em>But</em> I don't know what manipulators I added. How can I accomplish this?</p> <p>In other words, I'd like to be able to write something like this (psudocode/fantasy code):</p> <pre><code>std::something old_state = cout.current_manip_state(); cout &lt;&lt; hex; cout.restore_manip_state(old_state); </code></pre> <p>Is this possible?</p> <h2>EDIT:</h2> <p>In case you're curious, I'm interested in doing this in a custom <code>operator&lt;&lt;()</code> I'm writing for a complex type. The type is a kind of discriminated union, and different value types will have different manips applied to the stream.</p> <h2>EDIT2:</h2> <p>Restriction: I cannot use Boost or any other 3rd party libraries. Solution must be in standard C++.</p>
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    1. COSaving and restoring __all__ of a stream's state is quite elaborate. There's a state saver for streams by James Kanze out there somewhere on the web. (In general, when you need to know something about streams that isn't answered in [Langer & Kreft](http://www.angelikalanger.com/IOStreams/Reviews/devx.htm), try to find a statement by James Kanze or Dietmar Kühl. They're definitive.)
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    2. CO"_I cannot use Boost or any other 3rd party libraries._" Why not?
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    3. CO@curiousguy: It's too much to go in to in any depth in a comment, but long story short, we simply don't use Boost in our production environment. Basically, it's more than we want to maintain.
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