Linux使用hash_map遇到问题

#include <ext/hash_map>
using namespace __gnu_cxx;
class str_hash{
public:
size_t operator()(const string& str) const
{
unsigned long __h = 0;
for (size_t i = 0 ; i < str.size() ; i ++)
__h = 5*__h + str[i];
return size_t(__h);
}
};

class str_compare
{
public:
bool operator()(const string& str1,const string& str2)const
{return str1==str2;}
};
int main()
{

hash_map<string,string,str_hash,str_compare>::iterator iter=nouns.find(name);
if (iter == nouns.end())
{
cout<<iter->first<<endl;////每次都core在这里
}
}

每次都core的地方：
0x004cc43c in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () from /usr/lib/libstdc++.so.6

各位达人，请问这是神马原因呢？