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    <p>Stateful lambdas cannot be turned into function pointers.</p> <p>Only lambdas with no state can be turned into function pointers.</p> <p>Your state needs to slide in through some back door. <code>glutDisplayFunc</code>, only takes a stateless function pointer. Modifying it isn't possible.</p> <p>If you can find a back door to store something, you can use that to store an arbitrary lambda. In this case, <code>glutDisplayFunc</code> is associated with the current window. Is there any place you can shove state in the current window, and figure out which one that is?</p> <p>Suppose you find such a <code>void*</code>. Then simply allocate a <code>std::function&lt;void()&gt;</code>, shove it in there, and register the following lambda:</p> <pre><code>void AClass::b(void (*func)()) { auto funcA = [func] () { [that first low level operation]; func(); //Which is: void a(void); [the second low level operation]; }; registerPVoidSomewhere( new std::function&lt;void()&gt;( funcA ) ); register([]() { void* pVoid = getPVoidFromWhereIHideItAbove(); std::function&lt;void()&gt;* pFunc = reinterpret_cast&lt;std::function&lt;void()&gt;*&gt;( pVoid ); if (pFunc) { (*pFunc)(); }; } ); } </code></pre> <p>Now, I'm betting that when the <code>glutDisplayFunc</code> is called, it is called from a context when you can ask <code>glut</code> what the current window is. Maybe that window has a place for a user-defined <code>void*</code>, or you could have a global map from window pointer to <code>void*</code> that you manage (in that second case, you could even have a global map from window pointer to <code>std::function&lt;void()&gt;</code>, and get rid of that nasty casting).</p>
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    1. POHow to call in a function a lambda function as a parameter?
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    1. USYakk - Adam Nevraumont
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    1. COThis turns into something ugly :) May be I should better keep those functions in the "void a" function?
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      1. USLilian A. Moraru
    2. CO@LilianA.Moraru A function with signature `void()` *has no state* to keep things, unless you shove things into global variables, or do atrocious hacks. Hence the need for a back-door state. I'm betting that there is back-door state in your case, and that is the intended way to handle state for the callback function.
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      1. USYakk - Adam Nevraumont
    3. CONo global variables or atrocious hacks... That's why I don't really want to go the road of this solution. I wanted to keep it clean and simple. Glut can do those 2 operations from anywhere after it was initialized. I am not doing any hacks/global variables... For example, you could compare it to how Botan works. Initialize the pipe and than from wherever you call the Botan functions it will affect one single point, you don't have to pass variables around.
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      1. USLilian A. Moraru
 

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