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    <p>Has anyone noticed that the <a href="https://stackoverflow.com/a/282433/20003">accepted answer</a> only works with trivial cases? The only way that function&lt;>::target() will return an object that can be bound to a C callback, is if it was constructed with an object that can be bound to a C callback. If that's the case, then you could have bound it directly and skipped all of the function&lt;> nonsense to begin with.</p> <p>If you think about it, there isn't any magic solution to this. A C-style callback is stored as a single pointer which points to executable code. Any nontrivial boost::function&lt;> is going to need at least two pointers: one to the executable code, the other to the data that's needed to set up the call (e.g. the 'this' pointer, in the case of a bound member function). </p> <p>The right way to use boost::function and boost::bind with C callbacks is to create a shim function that satisfies the callback signature, figures out which function&lt;> to call, and calls it. Usually C callbacks will have some kind of a void* for 'user data'; that's where you stash your function pointer:</p> <pre><code>typedef void (*CallbackType)(int x, void* user_data); void RegisterCallback(CallbackType cb, void* user_data); void MyCallback(int x, void* userData) { boost::function&lt;void(int)&gt; pfn = static_cast&lt;boost::function&lt;void(int)&gt; &gt;(userData); pfn(x); } boost::function&lt;void(int)&gt; fn = boost::bind(myFunction(5)); RegisterCallback(MyCallback, &amp;fn); </code></pre> <p>Of course, if your callback signature doesn't include some kind of user data pointer, you're out of luck. But any callback that doesn't include a user data pointer is already unusable in most real-world scenarios, and needs to be rewritten.</p>
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    1. CO'boost::function<void(int)> pfn = static_cast<boost::function<void(int)> >(userData);' should use boost::function* instead or there will be compile error?
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