在std :: upper_bound中的boost :: transform_iterator编译错误

Question

I have a list of nodes sorted by z-order ( http://en.wikipedia.org/wiki/Z-order_curve ). I am trying to find the first node bigger than zPosition. The iterTransform object takes an iterator and returns a binary position representation (same type as zPosition). This type can be compared by pathCmp

NodeIterT last = std::upper_bound(
    boost::make_transform_iterator(begin, iterTransform), // return PathType
    boost::make_transform_iterator(end, iterTransform),
    zPosition,
    pathCmp ); // takes two PathType arguments

when compiling this I get

error C2440: 'initializing' : cannot convert from 'boost::transform_iterator < UnaryFunc,Iterator,Reference,Value > ' to 'std::_Vector_iterator<_Myvec>'

Is there any mistake in this minimized example or do I need to provide more code?

Answer 1

std::upper_bound returns a transform_iterator . Add .base() to get the iterator type that you wrapped:

NodeIterT last = std::upper_bound(
boost::make_transform_iterator(begin, iterTransform), // return PathType
boost::make_transform_iterator(end, iterTransform),
zPosition,
pathCmp ).base();

should work assuming begin and end are of NodeIterT type.

Answer 2

std::upper_bound returns an iterator with the same type as those given as parameters. In your case, the return type is therefore boost::transform_iterator<...> and not std::vector<...>::iterator .

If you want to access the underlying iterator, you can use the base() member function :

NodeIterT last = std::upper_bound(
    boost::make_transform_iterator(begin, iterTransform), // return PathType
    boost::make_transform_iterator(end, iterTransform),
    zPosition,
    pathCmp ).base(); // note the call to base()