Map in C++ give the key and get the string [closed] - c++

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I have created a map like this : std::map<int, std::string> mapID;
INPUT: mapID[1] = "string!";
and I want to print element with the key is the s.
For example
cout << "The string is : " << mapID.at(s)->second << endl;
OR
cout << "The string is : " << mapID.find(s)->second << endl;
But I have the error
error: no matching function for call to ‘std::map >::at(std::string&)’
UPDATE:
while(getline(file,s))
{
cout<< s << endl;
number = atoi(s.c_str());
cout << "The string is: " << mapID.at(number)<< endl;
}

Answer 1

If you look at the reference http://en.cppreference.com/w/cpp/container/map/at you will see, that method "at" returns a second element of pair. In your case it is std::string.
The code should be
cout << "The string is : " << mapID.at(1) << endl;

Answer 2

Since C++11, .at() returns a reference to the mapped value of the element identified with key k.
Your example was good if you used an iterator as you can then access your pair element made by your map.
Here is an example with an iterator
auto it = mapID.find(1);
cout << "The string is : " << it->second << endl;
OR with .at()
cout << "The string is : " << mapID.at(1) << endl;
But beware that .at() will throw if the element is not found in your map as it can't create it like the [] operator