find声明：
template<class InputIterator, class Type>
InputIterator find(
InputIterator _First,
InputIterator _Last,
const Type& _Val
);
示例：
void test_find()
{
std::list <int> L;
std::list <int>::iterator Iter;
std::list <int>::iterator result;
L.push_back(40);
L.push_back(20);
L.push_back(10);
L.push_back(30);
L.push_back(10);
std::copy(L.cbegin(), L.cend(), std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
result = std::find(L.begin(), L.end(), 10);
if (result == L.end())
std::cout << "There is no 10 in list L.";
else {
std::cout << "There is a 10 in list L";
if (++result != L.end())
std::cout << " and it is followed by a " << *result << ".";
}
std::cout << std::endl;
}