How to store a hash table in a file?

What language are you using? The common method is to do some sort binary serialization.

Ok, I see you have edited to add the language. For C++ there a few options. I believe the Boost serialization mechanism is pretty good. In addition, the page for Boost's serialization library also describes alternatives. Here is the link:

http://www.boost.org/doc/libs/1_37_0/libs/serialization/doc/index.html

Assuming C/C++: Use array indexes and fixed size structs instead of pointers and variable length allocations. You should be able to directly write() the data structures to file for later read()ing.

For anything higher-level: A lot of higher language APIs have serialization facilities. Java and Qt/C++ both have methods that sprint immediately to mind, so I know others do as well.

You could just write the entire data structure directly to disk by using serialization (e.g. in Java). However, you might be forced to read the entire object back into memory in order to access its elements. If this is not practical, then you could consider using a random access file to store the elements of the hash table. Instead of using a pointer to represent the next element in the chain, you would just use the byte position in the file.