In C++ a class with at least one pure virtual function is called abstract class. You can not create objects of that class, but may only have pointers or references to it. If you are deriving from an abstract class, then make sure you override and define all pure virtual functions for your class. From … Read more
Yes, the code has a memory leak unless you delete the pointers. If the foo class owns the pointers, it is its responsibility to delete them. You should do this before clearing the vector, otherwise you lose the handle to the memory you need to de-allocate. You could avoid the memory management issue altogether by … Read more
I’m going to attempt to explain this without making any mistakes, but I’m betting this will attract a clarification or two in the comments. A data frame is a list. When you subset a data frame using the name of a column and [, what you’re getting is a sublist (or a sub data frame). If you want … Read more
You need to pass by reference; by making a copy, you sort a temporary copy, and then that’s it; it disappears and the original is still unsorted, because, once again, you sorted only a temporary copy of the entire vector. So change vector<int> a to vector<int>& a. Here’s the code, fixed: http://coliru.stacked-crooked.com/a/2f118555f585ccd5
Use the vector::size() method: i < v.size(). The sizeof operator returns the size in bytes of the object or expression at compile time, which is constant for a std::vector.
There is an idiomatic way for printing a vector out. This way is safe and doesn’t require you to keep track of the vectors size or anything like that. It is also easily recognisable to other C++ developers. This method works on other container types too that do not allow random access. This works both … Read more
Again, I’ll remind that I might be missing something, but I think this is pretty simple addition of vectors:
If you want to rotate a vector you should construct what is known as a rotation matrix. Rotation in 2D Say you want to rotate a vector or a point by θ, then trigonometry states that the new coordinates are To demo this, let’s take the cardinal axes X and Y; when we rotate the X-axis 90° counter-clockwise, … Read more
When I do this: Everything works great. However, when I make it a vector of references instead: I get horrible errors like error C2528: ‘pointer’ : pointer to reference is illegal I want to put a bunch of references to structs into a vector, so that I don’t have to meddle with pointers. Why is … Read more
erase invalidates the iterator. You can’t use it any more. Luckily for you, it returns an iterator that you can use: Or: Are you responsible for freeing the memory referred to by the pointers in the vector? If that’s the reason that you’re iterating (and your real program has more code that you haven’t shown, … Read more