Re: cout << vector<string>

From:
Jeff Schwab <jeff@schwabcenter.com>
Newsgroups:
comp.lang.c++
Date:
Fri, 07 Nov 2008 07:32:50 -0500
Message-ID:
<Q72dnf5yWqjvqInUnZ2dnUVZ_vCdnZ2d@giganews.com>
Pete Becker wrote:

On 2008-11-07 06:03:15 -0500, Maxim Yegorushkin
<maxim.yegorushkin@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';
}

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