CODEWITHSUNDEEP
c++operatorsoperator-overloadingpriority-queueconditional-operator
Sterling
Sterling

Reputation: 4213

Overloading operator< for priority queue

I am trying to make a priority queue of a class I made like this - 

std::priority_queue<Position> nodes;

I overloaded the < operator in Position like this - 

bool Position::operator<(Position& right) {
    return (fvalue < right.getFValue());
}

However, whenever I try to compile I get this error message saying the < operator is not overloaded - 

error: no match for ‘operator<’ in ‘__x < __y’
position.h:30: note: candidates are: bool Position::operator<(Position&)

What am I missing here? Any help is appreciated.

Upvotes: 5

Views: 7966

Answers (2)

JohnMcG
JohnMcG

Reputation: 8805

  1. It's preferable not to overload the comparison operators just to satisfy a collection. (http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Operator_Overloading). It's better to use comparator objects or functions, if possible. If your operator defines how these objects are intrinsically ordered, rather than just what their priority should be in the queue, then it's OK. But if not, you could get into trouble if another developer uses your operator in another context.

  2. I'm not sure what fvalue is, but it's possible that it may not have operator < defined for it.

Upvotes: 0

Ben Voigt
Ben Voigt

Reputation: 283614

Relational operators shouldn't change the operands. Try:

bool Position::operator<(const Position& right) const {

My guess is that either __x or __y (or both) are const. You can't call a non-const member function on __x if it's const, also you can't pass __y as the right parameter if __y is const and right is not.

Upvotes: 15

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