Chapter 15. Designing and Implementing a “Minute/Hour Counter”

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Let’s take a look at a data structure used in real production code: a “minute/hour counter.” We’ll take you through the natural thought process an engineer might go through, first trying to solve this problem and then improving its performance and adding features. Most important, we’ll also be trying to keep the code easy to read, using principles from throughout this book. We might take some wrong turns along the way or make other mistakes. See if you can follow along and catch them.

The Problem

We need to keep track of how many bytes a web server has transferred over the past minute and over the past hour. Here’s an illustration of how these totals are maintained:

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It’s a fairly straightforward problem, but as you’ll see, solving it efficiently is an interesting challenge. Let’s start by defining the class interface.

Defining the Class Interface

Here is our first version of the class interface in C++:

class MinuteHourCounter {
    // Add a count
    void Count(int num_bytes);

    // Return the count over this minute
    int MinuteCount();

    // Return the count over this hour
    int HourCount();

Before we implement this class, let’s go through the names and comments to see if there’s anything we want to change. ...

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