bind1st & bind2nd

#include <iostream>
#include <functional>
#include <algorithm>
#include <vector>
using namespace std;

int main()
{
	vector<int> coll;
	for(int i = 1; i <= 13; ++i)
	{
		coll.push_back(i);
	}

	//查找元素值大于10的元素的个数
	//也就是使得10 < elem成立的元素个数
	int res = count_if(coll.begin(), coll.end(), bind1st(less<int>(), 10));
	cout<<"[10 < elem]: "<<res<<endl;

	//查找元素值小于10的元素的个数
	//也就是使得elem < 10成立的元素个数
	res = count_if(coll.begin(), coll.end(), bind2nd(less<int>(), 10));
	cout<<"[elem < 10]: "<<res<<endl;
	
	return 0;
}

/*
Output:

[10 < elem]: 3
[elem < 10]: 9
*/