Re: cout << vector<string>

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 7 Nov 2008 09:31:39 -0800 (PST)

Message-ID:

<45eef47e-3a64-43a9-ad33-9132a2af73f5@k1g2000prb.googlegroups.com>

On Nov 7, 1:32 pm, Jeff Schwab <j...@schwabcenter.com> wrote:

Pete Becker wrote:

On 2008-11-07 06:03:15 -0500, Maxim Yegorushkin
<maxim.yegorush...@gmail.com> said:

The example probably assumes there is an overloaded operator<<() for
std::ostream and std::vector<>, something like this:
    namespace std {

        template<class A1, class A2>
        ostream& operator<<(ostream& s, vector<A1, A2> const& vec)

Which has undefined behavior. You can only add template specializations
to namespace std when they depend on user-defined types.

The correct alternative, AIUI:

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>

template<typename T>
std::ostream& operator<<(std::ostream& out, std::vector<T> const& v) {
     if (!v.empty()) {
         typedef std::ostream_iterator<T> out_iter;
         copy(v.begin(), v.end() - 1, out_iter( out, " " ));
         out << v.back();
     }
     return out;
}

int main() {
     int const ints[] = { 1, 2, 3, 4 };
     std::cout << std::vector<int>( ints, ints + 4 ) << '\n';
}

Correct in what sense? It's OK for simple test, like this, but
it's certainly not something you'd allow in production code.

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