Here's the situation:
I have a Graph class written in C++ and I need to build Graph objects from Files. The problem is that Graph are memorized in files in a lot of different ways, so I was thinking about a function that, using the file extension, could invoke the correct procedure for building a Graph in a certain format. How should I proceed? Am I wrong or I can't just overload operator>> in my class?Thanks in advance.
operator>> is (should be) agnostic to any details of the stream from which it is extracting, so using this operator is probably the wrong tact.
The best way to do this would be:
graph_type load_from_file(const std::string& file_path) { //or use something like boost::filesystem::path
std::ofstream file { file_path };
if(endswith(file_path, ".graph") {
return deserialize_from_graph(ofstream);
}
if(endswith(file_path, ".g2") {
return deserialize_from_g2(ofstream);
}
//other formats here
//else throw
}
note, endswith is not from the standard library, boost however has an implementation in it's string algorithms.
How do you determine how the data is memorized. If it is just
the extension, all you need is a map
std::string→pointer_to_function. If the same
extension can have several different representations,
distinguished, for example, by the first couple of bytes in the
file, or information in some common header, you'll have to
differ the final choice until you've read these
bytes—again, a map to the a pointer to function will do
the trick.
Depending on the complexity of the formats to read, you may want to replace the pointer to a reader function with a pointer to a factory function, which returns an instance of a reader class, which derives from an abstract reader.
