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POWhat is the cost of using a pointer to member function vs. a switch?
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  1. POWhat is the cost of using a pointer to member function vs. a switch?
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    copied!<p>I have the following situation:</p> <pre><code> class A { public: A(int whichFoo); int foo1(); int foo2(); int foo3(); int callFoo(); // cals one of the foo's depending on the value of whichFoo }; </code></pre> <p>In my current implementation I save the value of <code>whichFoo</code> in a data member in the constructor and use a <code>switch</code> in <code>callFoo()</code> to decide which of the foo's to call. Alternatively, I can use a <code>switch</code> in the constructor to save a pointer to the right <code>fooN()</code> to be called in <code>callFoo()</code>. </p> <p>My question is which way is more efficient if an object of class A is only constructed once, while <code>callFoo()</code> is called a very large number of times. So in the first case we have multiple executions of a switch statement, while in the second there is only one switch, and multiple calls of a member function using the pointer to it. I know that calling a member function using a pointer is slower than just calling it directly. Does anybody know if this overhead is more or less than the cost of a <code>switch</code>?</p> <p>Clarification: I realize that you never really know which approach gives better performance until you try it and time it. However, in this case I already have approach 1 implemented, and I wanted to find out if approach 2 can be more efficient at least in principle. It appears that it can be, and now it makes sense for me to bother to implement it and try it. </p> <p>Oh, and I also like approach 2 better for aesthetic reasons. I guess I am looking for a justification to implement it. :) </p>
 

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