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    <p>I tested it.</p> <p>I can guess that <code>operator&lt;&lt;</code> cannot bind a temporary to a non-const reference, so any externally defined operator&lt;&lt; functions will not work on the Foo temporary, but any class member ones will so if <code>ostream</code> or <code>ostringstream</code> has any internal <code>operator&lt;&lt;</code> members they will work.</p> <p>Therefore it may be that the overload to a pointer is a member function whilst the special one for const char * is externally declared.</p> <p>The non-temporary can bind to the non-const reference for the more specialist overload.</p> <p>If you really need this you can workaround with a wrapper</p> <pre><code>class Foo : { mutable std::ostringstream oss; public: ~Foo() { std::cout &lt;&lt; oss.str(); } template&lt;typename T&gt; std::ostream&amp; operator&lt;&lt;( const T&amp; t ) const { return oss &lt;&lt; t; } }; </code></pre> <p>Tested and works. The first operator&lt;&lt; will return you the underlying stream.</p> <p>I tried this too but it coredumped:</p> <pre><code>class Foo : std::ostringstream { Foo &amp; nonconstref; public: Foo() : nonconstref( *this ) {} ~Foo() { std::cout &lt;&lt; str(); } template&lt;typename T&gt; std::ostream&amp; operator&lt;&lt;( const T&amp; t ) const { return nonconstref &lt;&lt; t; } }; </code></pre> <p>This also works:</p> <pre><code>class Foo : public std::ostringstream { public: Foo() {} ~Foo() { std::cout &lt;&lt; str(); } Foo&amp; ncref() { return *this; } }; int main() { Foo foo; foo &lt;&lt; "Test1" &lt;&lt; std::endl; Foo().ncref() &lt;&lt; "Test2" &lt;&lt; std::endl; } </code></pre>
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    1. COBeen there, done that, confirming. I also came up with workaround—just do `std::stringstream().flush() << "anything";`. The trick is, that `flush()` does nothing on a `stringstream`, but returns invocant via reference. On a side-note, since the `operator<<` returns just `std::ostream`, you'll have to `static_cast` it back to `stringstream` to get the result out of it.
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      1. USJan Hudec
    2. COI got another solution that doesn't call flush, but yes for a stringstream flushing is a no-op so works in this case.
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    3. COThat is a nasty problem, thanks for the explanation. Your first solution is not an option, because the template for `operator<<` will not work for `std::endl` - this was the reason why I tried using inheritance. I guess I will go with the last solution.
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      1. USBjörn Pollex
 

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