Re: Comparing version numbers

[Robert Eachus <rieachus@comcast.net>]

On Sunday, November 12, 2017 at 9:39:15 PM UTC-5, Victor Porton wrote:
> Not sure if it is quite on-topic, because it is more about general 
> programming ideas rather than about Ada. (However, a solution in Python or 
> Ruby or JavaScript would more likely used regexps than Ada.)
> 
> Suppose I have two version numbers of a software. I need to check which of 
> the two is greater.
> 
> Lexical order string comparison does not work:
> 
> "2.3" vs "11.4".
> 
> I could split it by "." and compare the numbers. But a component of a 
> version numbers may be nonnumeric like:
> 
> "1.2beta".
> 
> What to do?
> 
> It should work for example for all Debian packages containing interpreters 
> (for example, "2.7" for "python" package).

It is easy to do using Text_IO.  Assuming that the version numbers are in two strings, compare using Float_IO if the first character both is a digit, otherwise compare as strings.  If the results compare equal, discard the current character in both strings and try again.  I'd probably write it using a goto to emphasize that the case statement is rarely used, but that's a detail.  You might also special case the string "gamma," but that is even more of a detail.  (It only matters if someone decided to issue a fourth test version at one release level, and called the versions alpha, beta, gamma, and delta.  I've seen gamma versions on occasion, but never a delta or epsilon.)