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    <p>If you do not define a constructor, the compiler will define a default constructor for you. </p> <p>The implementation of this </p> <h3>default constructor is:</h3> <ul> <li>default construct the base class (if the base class does not have a default constructor, this is a compilation failure)</li> <li>default construct each member variable in the order of declaration. (If a member does not have a default constructor, this is a compilation failure).</li> </ul> <p>Note:<br> The POD data (int,float,pointer, etc.) do not have an explicit constructor but the default action is to do nothing (in the vane of C++ philosophy; we do not want to pay for something unless we explicitly ask for it).</p> <p>If no destructor/copy Constructor/Assignment operator is defined the compiler builds one of those for you (so a class always has a destructor/Copy Constructor/Assignment Operator (unless you cheat and explicitly declare one but don't define it)).<br> The default implementation is:</p> <h3>Destructor:</h3> <ul> <li>If user-defined destructor is defined, execute the code provided.</li> <li>Call the destructor of each member in reverse order of declaration</li> <li>Call the destructor of the base class.</li> </ul> <h3>Copy Constructor:</h3> <ul> <li>Call the Base class Copy Constructor.</li> <li>Call the copy constructor for each member variable in the order of declaration.</li> </ul> <h3>Assignment Operator:</h3> <ul> <li>Call the base class assignment operator</li> <li>Call the assignment operator of each member variable in the order of declaration.</li> <li>Return a reference to this.</li> </ul> <p>Note Copy Construction/Assignment operator of POD Data is just copying the data (Hence the shallow copy problem associated with RAW pointers).</p>
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    1. USMartin York
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    1. COFrom section 8.5 item 5 in the standard: _"To default-initialize an object of type T means: ... [if the T is POD] the object is zero-initialized."_ and from item 4 of the same section: _"To zero-initialize an object of type T means: if T is a scalar type, the object is set to the value 0 (zero), taken as an integral constant expression, converted to T"_ . For POD, if I am not mistaken, this means `int i = int();` concludes with `i == 0`
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    2. CO@wilhelmtell: That is when you __explicitly__ use the default initialized. In the above situation the POD types are not explicitly default initialized so there values are undefined. This is why I use the slightly more ambiguous term of default constructor.
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