C++ class(四)

//静态类成员
//为多个类对象共享
#include<iostream>
#include<vector>

using namespace std;


class Triangular
{
public:
	static bool is_elem(int);
	static void gen_elements(int length);
	static void gen_elements_to_vaule(int vaule);//成员函数只有在不访问任何非静态成员的基础上才能够被声明为static


private:
	static const  int  _max_elems = 1024;
	static vector<int>_elems;

};


bool Triangular::is_elem(int vaule)               //静态成员函数在类外定义时，无需重复加上static
{
	if (!_elems.size() || _elems[_elems.size() - 1] < vaule)
		gen_elements_to_vaule(vaule);
	vector<int>::iterator found_it;
	vector<int>::iterator end_it = _elems.end();

	found_it = find(_elems.begin(), end_it, vaule);
	return found_it != end_it;
}

void Triangular::gen_elements(int length)
{
	if (length < 0 || length > _max_elems) {
		cerr << "Triangular Sequence: oops: invalid size: "
			<< length << " -- max size is "
			<< _max_elems << endl;
		return;
	}

	if (_elems.size() < length)
	{
		int ix = _elems.size() ? _elems.size() + 1 : 1;
		for (; ix <= length; ++ix)
			_elems.push_back(ix*(ix + 1) / 2);
	}
}

void Triangular::gen_elements_to_vaule(int value)
{
	int ix = _elems.size();
	if (!ix) {
		_elems.push_back(1);
		ix = 1;
	}

	while (_elems[ix - 1] < value && ix < _max_elems)
	{
		//     cout << "elems to value: " << ix*(ix+1)/2 << endl;
		_elems.push_back(ix*(ix + 1) / 2);
		++ix;
	}

	if (ix == _max_elems)
		cerr << "Triangular Sequence: oops: value too large "
		<< value << " --  exceeds max size of "
		<< _max_elems << endl;

}

int main()
{
	char ch;
	bool more = true;

	while (more)
	{
		cout << "Enter value: ";
		int ival;
		cin >> ival;

		bool is_elem = Triangular::is_elem(ival);    //静态成员函数的调用方式

		cout << ival
			<< (is_elem ? " is " : " is not ")
			<< "an element in the Triangular series.\n"
			<< "Another value? (y/n) ";

		cin >> ch;
		if (ch == 'n' || ch == 'N')
			more = false;
	}
	return  0;
}