PostgreSQL, Second Edition

Defining the Data Type in C

We'll start out by defining the internal form for an FCUR value. As I mentioned before, you want to store three pieces of information for each value: the name of the currency (dollars, euros, yen, and so on), the number of units, and the exchange rate at the time the value was created. Why do you need to store the exchange rate with each value? Because exchange rates vary over time, and you need to know the rate at the time the value is created.

Because you are going to use the C programming language to implement the required conversion functions, you need to define a structure^[4] containing the three components. Listing 6.9 shows the first few lines of the implementation file:

^[4] This is not necessarily the most efficient ...