Question

I’m using two different libraries in my project, and both of them supply a basic rectangle struct. The problem with this is that there seems to be no way to insert a conversion between the types, so I can’t call a function in one library with the result from a function in the other. If I was the author of either of these, I could create conversions, from the outside, I can’t.

library a:

typedef struct rectangle { sint16 x; sint16 y; uint16 w; uint16 h; } rectangle; 

library b:

class Rect {   int x; int y; int width; int height;   /* ... */ }; 

Now, I can’t make a converter class, because C++ will only look for a conversion in one step. This is probably a good thing, because there would be a lot of possibilities involving creating new objects of all kinds of types.

I can’t make an operator that takes the struct from a and supplies an object of the class from b:

foo.cpp:123 error: ‘operator b::Rect(const rectangle&)’ must be a nonstatic member function

So, is there a sensible way around this?

edit:

I should perhaps also point out that I’d really like some solution that makes working with the result seamless, since I don’t expect to be that coder. (Though I agree, old-school, explicit, conversion would have been a good choice. The other branch, reinterpret_cast has the same problem..)

edit2:

Actually, none of the suggestions really answer my actual question, Konrad Rudolph seems to be correct. C++ actually can’t do this. Sucks, but true. (If it makes any difference, I’m going to try subclassing as suggested by CodingTheWheel.

Answer 1

If you can’t modify the structures then you have no alternative to writing a manual conversion function because overloading conversion operators only works within the class body. There’s no other way.