Modern C++ Programming with Test-Driven Development

2.2 The Soundex Class

Searching is a common need in many applications. An effective search should find matches even if the user misspells words. Folks misspell my name in endless ways: Langer, Lang, Langur, Lange, and Lutefisk, to name a few. I’d prefer they find me regardless.

In this chapter, we will test-drive a Soundex class that can improve the search capability in an application. The long-standing Soundex algorithm encodes words into a letter plus three digits, mapping similarly sounding words to the same encoding. Here are the rules for Soundex, per Wikipedia:[4]

1. Retain the first letter. Drop all other occurrences of ​a​, ​e​, ​i​, ​o​, ​u​, ​y​, ​h​, ​w​.

2. Replace consonants with digits (after the first letter):

   • ​b​, ​f​, ​p​, ​v​: 1