求字符串递增算法

[summersdw1]

求一个函数,原形string Add(string &readstring)

向函数传递"000001",返回"000002",当传递"999999"则返回"000001"
有没有短小精悍的算法?

[matrixdwy]

string Add(string &readstring) {
        const char* n = readstring.c_str();
	int m = atoi(n);
	m++;
	if(m == 1000000)
	   m = 000001;
	ostringstream oss;
	oss.setf(ios::right, ios::adjustfield);
	oss.fill('0');
	oss.width(6);
	oss << m;
	readstring = oss.str();
	return readstring;
}