qvector

I have a class B that creates an object of a class A and calls a method of the object. a.h #ifndef A_H #define A_H class A { public: A(int); void function(); }; #endif // A_H a.cpp #include "a.h" A::A(int x) { } void A::function(){ //Do something. } b.h #ifndef B_H #define B_H #include <QVector> #include <a.h> class B { public: B(int); QVector<A> list; }; #endif // B_H b.cpp #include "b.h" B::B(int y) { list.append(A(y)); list[0].function(); } The problem is that this does not compile. It returns "no matching function to call 'A:A()'". I know that this can be solved with a forward declaration

std::vector::size() returns a size_type which is unsigned and usually the same as size_t , e.g. it is 8 bytes on 64bit platforms. In constrast, QVector::size() returns an int which is usually 4 bytes even on 64bit platforms, and at that it is signed, which means it can only go half way to 2^32. Why is that? This seems quite illogical and also technically limiting, and while it is nor very likely that you may ever need more than 2^32 number of elements, the usage of signed int cuts that range in half for no apparent good reason. Perhaps to avoid compiler warnings for people too lazy to declare