Error reading characters of string C++

I am trying to store a value from a

vector<vector<string>> data;

into a const char* variable - declared in the .h file - in this way:

heightmapName = data[0][1].c_str();

When I debug the program I notice that the variable heightmapName return this

heightmapName 0xcdcdcdcd <Error reading characters of string.>  const char *

However, if I declare a new const char* and initialize it like this:

    const char* what = data[0][1].c_str();
    heightmapName = data[0][1].c_str();

what variable store the data just fine, while heightmapNamedoesn't.

This is the function:

void Configuration::fileParser(string fileName)
{
    vector<vector<string>> data;
    string line;
    string delimiter = " ";
    ifstream ss(fileName);
    if (ss)
    {
        while (getline(ss, line))
        {
            vector<string> dataLine;
            string token = line.substr(0, line.find(delimiter));
            string value = line.substr(line.find(delimiter) +1);
            dataLine.push_back(token);
            dataLine.push_back(value);
            data.push_back(dataLine);
        }
        ss.close();
    }
    //storeData(data);
    const char* ahah = data[0][1].c_str();
    heightmapName =    data[0][1].c_str();
}

Why is this happening? and how can I solve this?

ps. I am using visual studio 2017