invalid use of non-static member function
The simplest fix is to make the comparator function be static:
static int comparator (const Bar & first, const Bar & second);
^^^^^^
When invoking it in Count
, its name will be Foo::comparator
.
The way you have it now, it does not make sense to be a non-static member function because it does not use any member variables of Foo
.
Another option is to make it a non-member function, especially if it makes sense that this comparator might be used by other code besides just Foo
.
You must make Foo::comparator
static or wrap it in a std::mem_fun
class object. This is because lower_bounds()
expects the comparer to be a class of object that has a call operator, like a function pointer or a functor object. Also, if you are using C++11 or later, you can also do as dwcanillas suggests and use a lambda function. C++11 also has std::bind
too.
Examples:
// Binding:
std::lower_bounds(first, last, value, std::bind(&Foo::comparitor, this, _1, _2));
// Lambda:
std::lower_bounds(first, last, value, [](const Bar & first, const Bar & second) { return ...; });