The Core iOS Developer’s Cookbook, Fifth Edition

Rolling Your Own Expressions

Some standards organizations have published descriptions of exactly what makes up a legal value. Enterprising developers have transformed many of those descriptions into fairly portable regular expressions. Consider the following regular expression definition of a floating-point number:

^[+-]?[0-9]+[\.]?[0-9]*$

It’s not a perfect definition, but for many purposes, it’s a pretty good one—and a flexible one to boot. It accepts a pretty good range of floating-point numbers with optional signs at the start. Admittedly, as presented, it won’t accept –.75, but it will also not accept –., which I think offers a fair compromise because –0.75 isn’t too hard for the user to guess. Alternatively, you could use a set of regular ...