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copied!<blockquote> <p>What is the difference between an ordinary function and a static function "in terms of memory allocation only" ?</p> </blockquote> <p>Nothing. A static function is just like a global function except for the scope.</p> <p>Even for non-static member functions, there's no extra memory required. The member function <code>int C::f(int arg1, int arg2)</code> is just syntactic sugar for something like <code>int C__f(C* this, int arg1, int arg2)</code>.</p> <blockquote> <p>What if the member function contains some local variables ? In that case the function "should" have a separate copy of that variable - specific to the object invoking the function...</p> </blockquote> <p>There's a copy of the local variables for <em>each invocation</em> of the function (unless they're <code>static</code>). This is why recursion in possible in C++.</p> <blockquote> <p>How is this problem solved in C++ ?</p> </blockquote> <p>Function calls are based around "stack frames". A stack frame consists of:</p> <ul> <li>The arguments to the function (including the implicit <code>this</code> if applicable).</li> <li>Any other non-<code>static</code> local variables in the function.</li> <li>The "return address", which tells the processor where to resume execution once the function is done.</li> </ul> <p>Whenever a function is called, a stack frame is created. When the function is, the stack frame is destroyed. If a function is called recursively, each level of recursion gets its own stack frame. For example, if you have</p> <pre><code>int factorial(int n) { if (n <= 1) return 1; else return factorial(n - 1) * n; } </code></pre> <p>Then when you call <code>factorial(3)</code>, a stack frame gets created like so:</p> <pre><code>------------------------ stack pointer (SP) n = 3 RA = <in main()> </code></pre> <p>When the recursive call is made to <code>factorial(2)</code>, an additional frame is added to the top of the stack</p> <pre><code>------------------------ SP n = 2 RA = <in factorial()> ------------------------ n = 3 RA = <in main()> </code></pre> <p>Another recursive call is made, to <code>factorial(1)</code>.</p> <pre><code>------------------------ SP n = 1 RA = <in factorial()> ------------------------ n = 2 RA = <in factorial()> ------------------------ n = 3 RA = <in main()> </code></pre> <p>This is the base case for the recursion, and the return value of 1 is stored in a register. The function call being complete, the top stack frame is destroyed, and execution continues at saved return address.</p> <pre><code>------------------------ SP n = 2 RA = <in factorial()> ------------------------ n = 3 RA = <in main()> </code></pre> <p>Now, the call to <code>factorial(2)</code> can compute its return value (2), and another stack frame can be destroyed:</p> <pre><code>------------------------ SP n = 3 RA = <in main()> </code></pre> <p>Finally, we can compute the result of the original function call (6), and destroy this stack frame too.</p>

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