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POC++ Casting Operators and traditional C casting operators
 

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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/332030/when-should-static-cast-dynamic-cast-and-reinterpret-cast-be-used">When should static_cast, dynamic_cast and reinterpret_cast be used?</a> </p> </blockquote> <p>I have done a lot of googling to find about:</p> <ol> <li>why to use C++ casting operators over traditional C style casting operators? </li> <li>When to use C++ casting operators, some live examples?</li> </ol> <p>The following is what I found: </p> <ul> <li>Traditionally any C++ casting operators is used for better maintenance of your code (ie) we can easily find where casting is used in code by just searching for this complex notation (reinterpret_cast&lt;) unlike C style casting operators. </li> </ul> <p><em>Now let me brief state why and when for each of the C++ casting operators</em> </p> <p><strong>static_cast:</strong></p> <p>Why use it over C style casting? <code>static_cast</code> is used to perform conversion between related types.</p> <p>Examples : </p> <pre><code> Class A {}; Class B {}; A* a = new A(); B* b = static_cast&lt;B*&gt;(a); // Compiler error B* b1 = (A*)a; // Works fine float f; int addr = (int)(&amp;f); // Works fine int addr = static_cast&lt;int&gt;(&amp;f); // Compiler error </code></pre> <p>But I wanted to know a real use case of when to use above code?</p> <p><strong>reinterpret_cast :</strong></p> <p><code>reinterpret_cast</code> casts pointers to unrelated types.</p> <p>Examples:</p> <pre><code> Class A {}; Class B {}; A* a = new A(); B* b = reinterpret_cast&lt;B*&gt;(a); // Works fine B* b1 = (A*)a; // Works fine float f; int addr = (int)(&amp;f); // Works fine int addr = reinterpret_cast&lt;int&gt;(&amp;f); // Works fine int ai = 10; float af = 13.33; // Would depend on how floating point is stored in machine // int&amp; since reinterpret_cast expects either the type or operand to be pointer or reference int ki = reinterpret_cast&lt;int&amp;&gt;(af); // ki would not be 13 int kitemp = (int)af; // kitemp would be 13 // The same reinterpret_cast behaviour can be achieved using this, int* in = (int*)(af); cout &lt;&lt; (*in); </code></pre> <p>My question is how else is <code>reinterpret_cast</code> different from C style casting? I'm unable to find why to use it over traditional casting operators and also when to use it?</p> <p>Another important example which makes these operators worse is:</p> <pre><code> const unsigned int * p; (int*)p; // Would remove unsigned and const at one shot // Using C++ casting operators // Const_cast expects a pointer or a reference reinterpret_cast&lt;int*&gt;(const_cast&lt;unsigned int* &gt;(p)); </code></pre> <p>Writing the above code to remove <code>const</code> and <code>unsigned</code> is much more complex in C++ casting? Then why do people use <code>reinterpret_cast</code>, <code>const_cast</code> or <code>static_cast</code> over tradional C casting operators?</p> <p>I do understand about <code>dynamic_cast</code> used in case of polymorphic classes; again this operator too has an extra cost of RTTI.</p>
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    1. COC++ casts are restricted versions of the C-style cast, which tries almost every cast until it finds one that works. You should use C++ style casts when you want a certain type of conversion to take place and for the compilation to fail if that type of conversion cannot happen, where C-style casts are for "just do it" casts.
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    2. CO@Mat : From the link you suggested, I got to understand a lot. But i had a doubt in the following, how would you map an example of this sort to C style casting, float a =13.33 ; int b = reinterpret_cast<int&>(a); ... Please make me understand this
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    3. CO@RishiMehta: I have no idea what that cast is supposed to _mean_. Why would you write such a "thing"?
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