stl_pred_compare.cpp

#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <vector>
#include <windows.h>
using namespace std;

class Timer {
public:
	Timer() : start_(), end_() {
	}

	void Start() {
		QueryPerformanceCounter(&start_);
	}

	void Stop() {
		QueryPerformanceCounter(&end_);
	}

	double GetElapsedMilliseconds() {
		LARGE_INTEGER freq;
		QueryPerformanceFrequency(&freq);
		return (end_.QuadPart - start_.QuadPart) * 1000.0 / freq.QuadPart;
	}

private:
	LARGE_INTEGER start_;
	LARGE_INTEGER end_;
};

Timer gtimer;

struct VecCompareFunctor {
	bool operator() (const int& lhs, const int& rhs)  {
		return lhs < rhs;
	}
};

bool VecCompareFun(const int& lhs, const int& rhs) {
	return lhs < rhs;
}

template <typename T>
void test_sort(size_t loops, size_t len, T comp) {
	double time_cost = 0.0;
	for (size_t i = 0; i < loops; ++i) {
		vector<int> vec;
		for (size_t i = 0; i < len; ++i) {
			vec.push_back(rand());
		}
		gtimer.Start();
		std::sort(begin(vec), end(vec), comp);
		gtimer.Stop();
		time_cost += gtimer.GetElapsedMilliseconds();
	}
	std::cout << loops << "\t\t" << len << "\t\t" << time_cost << std::endl;
}

void test() {
	const size_t karray_len[] = {
		100, 1000, 10000, 100000
	};
	const size_t krun_times[] = {
		100, 1000
	};
	std::cout << "use functor as pred" << std::endl;
	std::cout << "loops\t\t" << "len\t\t" << "time" << std::endl;
	for (auto len : karray_len) {
		for (auto run : krun_times) {
			test_sort(run, len, VecCompareFunctor());
		}
	}

	std::cout << "use function as pred" << std::endl;
	for (auto len : karray_len) {
		for (auto run : krun_times) {
			test_sort(run, len, VecCompareFun);
		}
	}
}

int main() {
	test();
	return 0;
}
/*
vs 2013 
Release Win32
use functor as pred
loops           len             time
100             100             0.533086
1000            100             6.62343
100             1000            8.84935
1000            1000            68.52
100             10000           93.2998
1000            10000           869.723
100             100000          1021.6
1000            100000          10312.9
use function as pred
100             100             0.721448
1000            100             7.1372
100             1000            12.0756
1000            1000            123.603
100             10000           156.273
1000            10000           1580.77
100             100000          1922.36
1000            100000          19511.9
*/