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POtype_traits segmentation fault with std::string
 

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    <p>Gathering the information from <a href="https://stackoverflow.com/questions/5768511/using-sfinae-to-check-for-global-operator">Using SFINAE to check for global operator&lt;&lt;?</a> and <a href="https://stackoverflow.com/questions/16505621/templates-decltype-and-non-classtypes">templates, decltype and non-classtypes</a>, I got the following code:</p> <p><a href="http://ideone.com/sEQc87" rel="nofollow noreferrer">http://ideone.com/sEQc87</a></p> <p>Basically I combined the code from both questions to call <code>print</code> function if it has <code>ostream</code> declaration, or to call the <code>to_string</code> method otherwise.</p> <p><strong>Taken from question 1</strong></p> <pre><code>namespace has_insertion_operator_impl { typedef char no; typedef char yes[2]; struct any_t { template&lt;typename T&gt; any_t( T const&amp; ); }; no operator&lt;&lt;( std::ostream const&amp;, any_t const&amp; ); yes&amp; test( std::ostream&amp; ); no test( no ); template&lt;typename T&gt; struct has_insertion_operator { static std::ostream &amp;s; static T const &amp;t; static bool const value = sizeof( test(s &lt;&lt; t) ) == sizeof( yes ); }; } template&lt;typename T&gt; struct has_insertion_operator : has_insertion_operator_impl::has_insertion_operator&lt;T&gt; { }; </code></pre> <p><strong>Taken from question 2</strong></p> <pre><code>template &lt;typename T&gt; typename std::enable_if&lt;has_insertion_operator&lt;T&gt;::value, T&gt;::type print(T obj) { std::cout &lt;&lt; "from print()" &lt;&lt; std::endl; } template &lt;typename T&gt; typename std::enable_if&lt;!has_insertion_operator&lt;T&gt;::value, T&gt;::type print(T obj) { std::cout &lt;&lt; obj.to_string() &lt;&lt; std::endl; } </code></pre> <p>Then my classes are like so:</p> <pre><code>struct Foo { public: friend std::ostream&amp; operator&lt;&lt;(std::ostream &amp; os, Foo const&amp; foo); }; struct Bar { public: std::string to_string() const { return "from to_string()"; } }; </code></pre> <p>And test output:</p> <pre><code>int main() { print&lt;Foo&gt;(Foo()); print&lt;Bar&gt;(Bar()); //print&lt;Bar&gt;(Foo()); doesn't compile //print&lt;Foo&gt;(Bar()); doesn't compile print(Foo()); print(Bar()); print(42); print('a'); //print(std::string("Hi")); seg-fault //print("Hey"); //print({1, 2, 3}); doesn't compile return 0; } </code></pre> <p>The <code>print(std::string("Hi"));</code> line seg-faults. Can anyone tell me why?</p>
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    1. COWhat has your rep done to you that you're handing it out so eagerly? :)
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    2. CO@jrok: I'm sensing an experiment of the type "How do good-but-low-rep users get treated"...?
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