这个错误怎么解决，求助，error C2679: binary '<<'
#include<map>
#include<algorithm>
#include<iterator>
#include<string>
#include<iostream>
using namespace std;
typedef map<string, int> months_type;
template <class First,class Second>
ostream& operator<<(ostream& out,const pair<First,Second> &p)
{
cout<<p->first<<" has "<<p->second<<" days";
return out;
}
ostream& operator<<(ostream& out,const months_type & l)
{
copy(l.begin(),l.end(),ostream_iterator<months_type::value_type>(cout,";"));
return out;
}
void main()
{
months_type months;
typedef months_type::value_type value_type;
months.insert(value_type(string("January"),31));
months.insert(value_type(string("February"),28));
months.insert(value_type(string("April"),30));
months.insert(value_type(string("March"),31));
cout<<months<<endl;

}
//编译时的错误
//error C2679: binary '<<' : no operator defined which takes a right-hand operand of type 'const struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class st



[解决办法]
因为ostream_iterator会寻找operator<<，而std namespace里面有很多operator<<，因此编译器不会去全局空间查找operator<<。也就是说，std::operator<<隐藏了::operator<<。把operator<<放入std namespace即可编译通过。

C/C++ code

#include<map>#include<algorithm>#include<iterator>#include<string>#include<iostream>using namespace std;typedef map<string, int> months_type;namespace std{    template <class First,class Second>    ostream& operator<<(ostream& out, const pair<First,Second> &p)    {        cout<<p.first<<" has "<<p.second<<" days";        return out;    }    ostream& operator<<(ostream& out,const months_type & l)    {        copy(l.begin(), l.end(), ostream_iterator<months_type::value_type>(out, ";\n"));        return out;    }}void main(){    months_type months;    typedef months_type::value_type value_type;    months.insert(value_type(string("January"),31));    months.insert(value_type(string("February"),28));    months.insert(value_type(string("April"),30));    months.insert(value_type(string("March"),31));    cout<<months<<endl;}