Function Object
Binary function object that returns true if its first argument is less than its second
#include<functional>
template <class T> struct less : public binary_function<T, T, bool> ;
less is a binary function object. Its operator() returns true if x is less than y. You can pass a less object to any algorithm that requires a binary function. For example, the transform algorithm applies a binary operation to corresponding values in two collections and stores the result of the function. less would be used in that algorithm in the following manner:
vector<int> vec1;
vector<int> vec2; vector<int> vecResult; . . . transform(vec1.begin(), vec1.end(), vec2.begin(), vecResult.begin(), less<int>());
After this call to transform, vecResult(n) will contain a "1" if vec1(n) was less than vec2(n) or a "0" if vec1(n) was greater than or equal to vec2(n).
template <class T>
struct less : binary_function<T, T, bool> { typedef typename binary_function<T, T, bool>::second_argument_type second_argument_type; typedef typename binary_function<T, T, bool>::first_argument_type first_argument_type; typedef typename binary_function<T, T, bool>::result_type result_type; bool operator() (const T&, const T&) const; };
If your compiler does not support default template parameters, then you need to always supply the Allocator template argument. For instance, you'll have to write :
vector<int, allocator>
instead of
vector<int>
binary_function, Function Objects