c++stlequalityequivalencestrict-weak-ordering

Can you use std::less_equal with std::sort even though it isn't a strict weak ordering?

From http://stdcxx.apache.org/doc/stdlibref/less-equal.html:

You can pass a less_equal object to any algorithm that requires a binary function. For example, the sort() algorithm can accept a binary function as an alternate comparison object to sort a sequence. less_equal would be used in that algorithm in the following manner: 
vector<int> vec1;
sort(vec1.begin(), vec1.end(), less_equal<int>());

Now I am confused, is the documentation above correct ?

Solution

  • You are right, std::sort requires the comparer to define a strict weak ordering.

    Which means that std::less_equal should not be used with std::sort. It can still be used with a number of other standard algorithms though, which take a binary function and which do not have the strict weak ordering requirement.