kenny@uiucdcsb.cs.uiuc.edu (12/05/86)
In working over the material of the previous posting, removing any references to overloaded functions, I discovered that I couldn't find a syntax that cfront would accept for taking the address of a constructor. I want to do this because I am in a situation where I have allocated memory by another means that I want to initialize as an instance of a class, so I want to pass it to the constructor as ``this''. The reason why is complicated; suffice it to say that I am dealing with a situation where I can't rewrite the constructor and have to use a memory allocator other than the standard _new operator. Kevin Kenny UUCP: {ihnp4,pur-ee,convex}!uiucdcs!kenny Department of Computer Science ARPA: kenny@B.CS.UIUC.EDU (kenny@UIUC.ARPA) University of Illinois CSNET: kenny@UIUC.CSNET 1304 W. Springfield Ave. Urbana, Illinois, 61801 Voice: (217) 333-8740
bs@alice.UUCP (12/08/86)
Kevin Kenny writes > In working over the material of the previous posting, removing any > references to overloaded functions, I discovered that I couldn't find > a syntax that cfront would accept for taking the address of a > constructor. I want to do this because I am in a situation where I > have allocated memory by another means that I want to initialize as an > instance of a class, so I want to pass it to the constructor as > ``this''. The reason why is complicated; suffice it to say that I am > dealing with a situation where I can't rewrite the constructor and > have to use a memory allocator other than the standard _new operator. That sounds messy - and no, there is no way of taking the address of a constructor, if you must play games with allocation and initialization that separates the two you will have to do something like providing a separate ``init()'' function and pass the address of it. If you cannot even do that I think you will have to avoid user-defined allocation. Similarly for destructors.
shopiro@alice.UUCP (12/08/86)
Try writing a public derived class with a constructor and destructor and putting your allocation there. -- Jonathan Shopiro AT&T Bell Laboratories, Murray Hill, NJ research!shopiro (201) 582-4179
mikem@otc.OZ (Michael Mowbray) (12/09/86)
In article <165700002@uiucdcsb>, kenny@uiucdcsb.cs.uiuc.edu writes: > I discovered that I couldn't find a syntax that cfront would accept for > taking the address of a constructor. I want to do this because I am in > a situation where I have allocated memory by another means that I want > to initialize as an instance of a class, so I want to pass it to the > constructor as ``this''. Sounds contrary to C++ philosophy to me. There have been times when I would have liked to do this, but I eventually realised that it just reflected bad design. (Of course, I don't know the constraints applying in this particular case.) > The reason why is complicated; suffice it to say that I am > dealing with a situation where I can't rewrite the constructor and > have to use a memory allocator other than the standard _new operator. You could possibly do the following, but I'd try to re-structure the design in preference. class Given { // The class you're interested in. int i; public: Given(int ii); // - can't be re-written, say. }; struct Aux : public Given { // Auxiliary class Aux(void* buf, int ii) : (ii) // buf must have correct size & alignment { this = (this==0) ? (Aux*)buf : this; } }; main() { int buffer[sizeof(Given)/sizeof(int)]; // Or use space which the // non-standard allocator gave. Given *g = (Given*)(new Aux(buffer,1)); // we want a Given with i=1, say. } - not really recommended.