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POCopy a callback?
 

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  1. POCopy a callback?
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    <p>Is it possible to copy the callback of one object into another?</p> <p>Right now I'm dealing with a data structure with a member like the following:</p> <pre><code>class Obj { // some unrelated variables // some unrelated functions void (*callback)(Obj&amp; r, void* user); void* callback_data; } </code></pre> <p>The callback is assigned like the following:</p> <pre><code>o-&gt;callback = AFunctionInAnotherScope; </code></pre> <p>A vector of <code>Obj</code> is kept but a <code>clear()</code> has to be invoked on that vector every iteration.</p> <p>The callback function is in another scope which also assigns the callback.</p> <p>The current scope has no access to the callback function but I'd like to create new Obj and assign them the same callback. Is there a way to do this?</p> <p>e: So far I've tried using <code>memcpy(&amp;copyObj, &amp;vectorOfObj.at(0), sizeof(Obj));</code> but I don't think I used that properly.</p> <p>Thanks in advance.</p> <p>Update: Here is what the file that creates the Obj looks like:</p> <p><strong>Caller.cpp</strong></p> <pre><code>#include "SomeClass.h" void Callback(Obj&amp; r, void* dummy_data) { // do things } int main( int argc, char* argv[] ) { for(int i = 0; i &lt; SomeClass::vectorOfOBj.size(); ++i) { vectorOfObj.at(i).callback = Callback; } } </code></pre> <p>Later on, in another file that doesn't have access to Caller.cpp but does have access to SomeClass.h</p> <pre><code>#define VAR(V,init) __typeof(init) V=(init) #define FOR_EACH(I,C) for(VAR(I,(C).begin());I!=(C).end();I++) void Run() { FOR_EACH(o, vectorOfObjects) { Obj &amp;b = *o; r-&gt;callback(b, o-&gt;callback_data); } vectorOfObjects.clear(); // repopulate vectorOfObject, might not be the same size as before. Could be bigger } </code></pre>
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    1. COYou should not use `memcpy` for class objects. You should, however, be able to make a copy using the copy constructor. The compiler will create one by default if you don't define one explicitly.
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      1. USCody Gray
    2. CO@CodyGray: To be more precise, you should not use `memcpy` (and his friends `malloc`, `realloc`, `strcpy`, `free`) on non-POD types. C structures are class objects, too, but they are POD. But indeed it's a good rule of thumb (and I would go so far to call it good practice for the average task) to not call those functions for any object, if applicable.
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      1. USSebastian Mach
    3. COI left out the technical details because there's no reason to use `memcpy` on class objects at all in C++. This isn't a question about C. (whoops, you already caught that on your edit)
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      1. USCody Gray
 

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