Final answer:
The abstract base class for streams dealing with character input in C++ is std::basic_istream, which provides foundational functionality for derived classes like std::istream and std::ifstream.
Step-by-step explanation:
The name of the abstract base class for streams dealing with character input in C++ is std::basic_istream. This class template serves as a base for input stream classes like std::istream, which is typically used with standard types such as char for std::ifstream, the class used for reading from files.
By using the inheritance feature of object-oriented programming, std::istream and other classes that derive from std::basic_istream can provide specific functionalities for character input requirements.