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POClass imitating a "pointer to a reference" can save out of scope variables?
 

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  1. POClass imitating a "pointer to a reference" can save out of scope variables?
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    <p>I thought of a strange cheat in C++. Normally, I can't smuggle a reference out of a scope because I can't define an uninitialized reference in the containing scope. However, I can define a pointer to a class containing a reference, fail to initialize it, and then assign it the address of some dynamic memory initialized to a local variable. Even though that dynamic object contains a reference to a variable that is supposed to go out of scope, the pointed-to object still has a valid reference with the same value! g++ doesn't complain even if I tell it to be <code>-pedantic</code>, so I assume it's valid. But how, and why?</p> <pre><code>struct int_ref { int &amp;x; int_ref(int &amp;i): x(i) {} }; #include &lt;iostream&gt; using namespace std; int main(void) { int_ref *irp; int i = 1; int_ref a(i); // Creates an int_ref initialized to i irp = &amp;a; // irp is now a pointer to a reference! // Prints 1 cout &lt;&lt; "irp-&gt;x = " &lt;&lt; irp-&gt;x &lt;&lt; " (i = " &lt;&lt; i &lt;&lt; ")" &lt;&lt; endl; i = 2; // Prints 2 cout &lt;&lt; "irp-&gt;x = " &lt;&lt; irp-&gt;x &lt;&lt; " (i = " &lt;&lt; i &lt;&lt; ")" &lt;&lt; endl; int j = 3; int_ref b(j); irp = &amp;b; // Prints 3 cout &lt;&lt; "irp-&gt;x = " &lt;&lt; irp-&gt;x &lt;&lt; " (i = " &lt;&lt; i &lt;&lt; ", j = " &lt;&lt; j &lt;&lt; ")" &lt;&lt; endl; i = 1; // Still prints 3 cout &lt;&lt; "irp-&gt;x = " &lt;&lt; irp-&gt;x &lt;&lt; " (i = " &lt;&lt; i &lt;&lt; ", j = " &lt;&lt; j &lt;&lt; ")" &lt;&lt; endl; { int k = 4; irp = new int_ref(k); // k goes out of scope } int k = 1; // Doesn't affect the other k, of course // Prints 4 ?! cout &lt;&lt; "irp-&gt;x = " &lt;&lt; irp-&gt;x &lt;&lt; " (i = " &lt;&lt; i &lt;&lt; ", j = " &lt;&lt; j &lt;&lt; ")" &lt;&lt; endl; } </code></pre> <p><strong>Edit:</strong> This may in fact be (as suggested in the answers) an undiagnosed dangling reference. What about if I define <code>int_ref</code> like this:</p> <pre><code>struct int_ref { const int &amp;x; int_ref(const int &amp;i): x(i) {} }; </code></pre> <p>A <code>const</code> reference need not refer to an lvalue, so there is no well-defined concept of a dangling one. Is the code still undefined?</p>
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    1. USRyan Reich
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