是否可以概括将STL容器作为参数的函数？

Question

I am new to generic functions in C++. I have a template function that prints the inside of a vector.

template<class T>
void print(vector<T> v){
    for(typename vector<T>::iterator it=v.begin(); it != v.end() ; it++)
        cout << *it << endl;
}

I want to write a more generic print() to print an STL container's inside. How can I proceed from this point on?

Answer 1

There's already a generic algorithm that can do that, using iterators for both the input and the output:

std::copy(v.begin(), v.end(), std::ostream_iterator<T>(std::cout, "\n"));

As such, I would proceed by using what's already there. If you really like the syntax of print(container_name); (which I'll admit is attractive), you could use this as the implementation, something like this:

template <class Container>
void print(Container const &c) { 
    std::copy(std::begin(c), std::end(c),
              std::ostream_iterator<typename Container::value_type>(std::cout, "\n"));
}

I'd note that (in C++11) it's often more convenient to use a range-based for loop than std::copy though:

template <class Container>
void print(Container const &c) { 
    for (auto const &item : c)
        std::cout << item << "\n";
}

Either of these should work for most real containers, though I'd generally prefer the latter, not only because it's simpler, but also because it's a little more generic. The first requires an actual container the defines a value_type member, so you can't apply it to a built-in array, for one example. You can remove that particular limitation by using std::iterator_traits<iterator>::value_type if you want to badly enough, but the latter avoids the problem entirely (and simplifies the code quite a bit in the process).