Thanks for a great library!
I noticed that if the .env file does not exist, it is silently ignored and there is no way to check if the file was actually found. I think the dotenv class should keep a status value to indicate if the file was found & parsed or not. There should be a way to query the status, for example:
env.load_dotenv();
if(!env.good()) throw std::runtime_error(".env file was not found"):