c++11 auto

在遍历容器时需要用到iterator，

std::map<std::string, std::vector<int>> map;
for(auto it = begin(map); it != end(map); ++it) 
{
}

可以用auto遍历map

for (auto &kv : myMap) {
    count<<kv.first<<" has value "<<kv.second<<endl;
}