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POSize of class instance
 

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    <p>I'm working with a class for which the new operator has been made private, so that the only way to get an instance is to write</p> <pre><code>Foo foo = Foo() </code></pre> <p>Writing</p> <pre><code>Foo* foo = new Foo() </code></pre> <p>does not work.</p> <p>But because I really want a pointer to it, I simulate that with the following :</p> <pre><code>Foo* foo = (Foo*)malloc(sizeof(Foo)); *foo = Foo(); </code></pre> <p>so that can test whether the pointer is null to know whether is has already been initialized.</p> <p>It looks like it works, from empirical tests, but is it possible that not enough space had been allocated by malloc ? Or that something else gets funny ?</p> <p><strong>--- edit ---</strong></p> <p>A didn't mention the context because I was not actually sure about why they the new operator was disabled. This class is part of a constraint programming library (gecode), and I thought it may be disabled in order to enforced the documented way of specifying a model.</p> <p>I didn't know about the Concrete Data Type idiom, which looks like a more plausible reason.</p> <p>That allocation scheme may be fine when specifying a standard model --- in which everything is specified as CDTs in the Space-derived class --- but in my case, these instance are each created by specific classes and then passed by reference to the constructor of the class that reprensents the model.</p> <p>About the reason i'm not using the</p> <pre><code>Foo f; Foo *pf = &amp;f; </code></pre> <p>it would be like doing <em>case 1</em> below, which throws a "returning reference to local variable" warning</p> <pre><code>int&amp; f() { int a=5; return a; } // case 1 int&amp; f() { int a=5; int* ap=&amp;a; return *ap; } int&amp; f() { int* ap=(int*)malloc(sizeof(int)); *ap=5; return *ap; } </code></pre> <p>this warning disappears when adding a pointer in <em>case 2</em>, but I guess it is because the compiler loses tracks.</p> <p>So the only option left is <em>case 3</em> (not mentioning that additionaly, <code>ap</code> is a member of a class that will be initialized only once when f is called, will be null otherwise, and is the only function returning a reference to it. That way, I am sure that <code>ap</code> in this case when lose its meaning because of the compilier optimizing it away (may that happen ?)</p> <p>But I guess this reaches far too much beyond the scope of the original question now...</p>
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    1. COWhy do you really want a pointer to it? Can't you do something like Foo foo = Foo(); Foo *fooPtr = &foo;
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      1. USHogan
    2. COI may be wrong, but doing it this way seems odd to me. Is `delete` private as well? Otherwise you'll have explicit `delete`s in your code but no `new`. That would be hard to keep track of.
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    3. COWhy don't you just do `&foo` to get the address of the object? why do you want to do `malloc`?
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      1. USNaveen
 

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