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copied!<p>When you declare an object of a class <code>myclass</code> like this:</p> <pre><code>myclass ob1(5); </code></pre> <p>it means that you've created it with the <strong>second</strong> constructor which accepts <code>int</code> parameter. In other words, you literally called the <strong>second</strong> constructor. By the way the object is created on stack.</p> <p>When you declare an object of a class <code>myclass</code> like this:</p> <pre><code>myclass ob1; </code></pre> <p>it means that you've created it with the <strong>first</strong> constructor which is parameterless. The right term for parameterless constructor is <strong>default</strong> constructor. In other words, you literally called the <strong>default</strong> (the <strong>first</strong> one) constructor. By the way the object is created on stack too (as in the previous case).</p> <p>When objects are created on stack they are destructed automatically when the object <strong>goes out of scope</strong>. The notion of <strong>scope</strong> applies to the <strong>blocks</strong> of code which include functions/methods/blocks. You can easily distinguish the block by a pair of curly brackets <code>{}</code>. For example:</p> <pre><code>void function() { myclass ob1; } // <--- think of ob1 being destructed at this point </code></pre> <p>the object <code>ob1</code> will go out of scope when function finishes execution and accordingly the destructor for <code>ob1</code> is <strong>automatically called</strong>. Another example:</p> <pre><code>void function() { while(true) { myclass ob1; } // <--- think of ob1 being destructed at this point // ob1 does not exist here! } </code></pre> <p>notice the infinite loop and the object <code>ob1</code> created inside it on every iteration. You can clearly see that curly brackets define a block which can combine multiple statements that constitute each iteration (currently there is only 1 statement). Accordingly, the object <code>ob1</code> will be automatically destructed in the end of each iteration.</p> <p>The notion of scope applies to class members too. For instance, say you have a class <code>wrapper</code>, and you declare <code>myclass</code> as its member (<code>m1</code>) in the following way:</p> <pre><code>class wrapper { public: myclass m1; }; </code></pre> <p>Then lets take one of the previous examples and create an object of <code>wrapper</code> on stack:</p> <pre><code>void function() { wrapper w; } // <--- destructor of w called first, destructor of w.m1 is called after </code></pre> <p>First the execution of the default constructor of <code>w</code> is started, during which <code>w.m1</code> is created (with default constructor in this case because I didn't specify in the constructor of <code>w</code> which constructor of <code>w.m1</code> I'd like to call). Then the constructor of <code>w</code> finishes the execution, and <code>w</code> can be deemed as officially created. The execution of <code>function</code> continues.</p> <p>When <code>function</code> finishes execution, <code>w</code> goes out of scope, and as you remember its destructor is called automatically then. As soon as the destructor of <code>w</code> finishes the execution, the destructor of <code>w.m1</code> is automatically called too. You can think of it as the object <code>w</code> has its own internal scope while it's alive, and a soon as it dies, all of its members go out of scope and should die too.</p>

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