How to read an initialization file.

I'm stuck on a problem in a program and I suspect one that I will keep encountering. I need to be able to read from an initialization file a set of values, as a simple example let us take three variables: base_dir, user_name, log_file. I need to be able to access these values effieiently and from virtually anywhere in the program. It would be nice to "at some point" open the file and read all these variables, all at once. Can anyone help?