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PODilemma with using value types with `new` operator in C#
 

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  1. PODilemma with using value types with `new` operator in C#
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    <p>When <code>operator new()</code> is used with reference type, space for the instance is allocated on the heap and reference variable itself is placed on the stack. Besides that, everything within the instance of reference type, that is allocated on the heap, is zeroed-out.<br> For example here is a class: </p> <pre><code>class Person { public int id; public string name; } </code></pre> <p>In the following code:</p> <pre><code>class PersonDemo { static void Main() { Person p = new Person(); Console.WriteLine("id: {0} name: {1}", p.id, p.name); } } </code></pre> <p><code>p</code> variable is on the stack and the created instance of <code>Person</code> (all of its memebers) is on the heap. <code>p.id</code> would be <code>0</code> and <code>p.name</code> would be <code>null</code>. This would be the case because everything allocated on the heap is zeroed-out.</p> <p>Now what I'm confused about is if I'm using a value type with <code>new</code> operator. For example, take into consideration following structure:</p> <pre><code>struct Date { public int year; public int month; public int day; } class DateDemo { static void Main() { Date someDate; someDate= new Date(); Console.WriteLine("someDate is: {0}/{1}/{2}", someDate.month, someDate.day, someDate.year); } } </code></pre> <p>Now I would like to know what do the following lines from main do:</p> <pre><code> Date someDate; someDate= new Date(); </code></pre> <p>In first line <code>someDate</code> variable is allocated on the stack. Precisely 12 bytes.<br> <strong>My question</strong> is what happens on the second line? What does <code>operator new()</code> do? Does it only zero-out members of <code>Date</code> structure or it allocates space on the heap as well? On one side I wouldn't expect <code>new</code> to allocate space on the heap, of course because in the first line memory is already allocated on the stack for the structure instance. On the other hand, I would expect <code>new</code> to allocate space on the heap and return address of that space, because that's what <code>new</code> should do. Maybe this is because I'm coming from C++ background. </p> <p>Nevertheless if the answer is: "when <code>new</code> is used with value types, it only zeroes-out members of object", than it's a bit inconsistent meaning of <code>new</code> operator because:</p> <ol> <li>when using <code>new</code> with value types, it only zeroes-out members of object on the stack</li> <li>when using <code>new</code> with reference types, it allocates memory on the heap for the instance and zerous-out it's members</li> </ol> <p>Thanks in advance,<br> Cheers</p>
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    1. COpossible duplicate of [Structure Vs Class in C#](http://stackoverflow.com/questions/203695/structure-vs-class-in-c)
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      1. USJon Skeet
    2. COAs well as the linked question, you might want to read this blog post: http://msmvps.com/blogs/jon_skeet/archive/2008/12/10/value-types-and-parameterless-constructors.aspx - I thought I'd seen one recently by Eric Lippert, but I can't find it now.
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      1. USJon Skeet
    3. CO@Jon Thanks. Was searching for it for a while, but couldn't find it. Maybe because the question, that you've linked, is not phrased the way it could easily be found when looked for?
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