On Mar 16, 2013 6:14 AM, "Ashley Sheridan" <ash@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, 2013-03-15 at 22:32 -0400, Andrew Ballard wrote: >> >> > Guess regex are the only useful solution here. When you consider to use >> > built-in functions, just remember, that for example '0xAF' is an integer >> > too, but '42.00' isn't. >> >> Shoot...I hadn't considered how PHP might handle hex or octal strings when >> casting to int. (Again, not in front of a computer where I can test it >> right now. ) >> >> Regexes have problems with more than 9 digits for 32-bit ints. I guess to >> some degree it depends on how likely you are to experience values that >> large. >> >> Andrew > > > Do they? Regex's deal with strings, so I don't see why they should have such issues. I've certainly never come across that problem, or heard of it before. > > Thanks, > Ash > http://www.ashleysheridan.co.uk > > Sure. If the string is nine or fewer digits, they can all be 0-9. If it is 10 digits, the first digit can only be 1-2. If it's 1, the remaining nine digits can still be 0-9, but if the first digit is 2, the second digit can only be 0-1. If the second digit is 0, the remaining eight digits can still be 0-9, but if it is 1, the third digit can only be 0-4. If the third digit is 0-3, the remaining seven digits can still be 0-9, but if it is 4, the fourth digit can only be 0-7. This pattern would continue for each of the remaining digits. Hopefully you get the idea. When you get to the final digit, its range depends not only on the nine preceding digits, but also the sign. If this is 64-bit, that adds even more wrinkles (including being aware of whether your implementation supports 64-bit ints). It may be possible to do with regular expressions, but it would definitely be complex and probably a time sink. As I said, if you KNOW you won't be dealing with integers that are more than nine digits, the regex should work fine. Remember, the OP didn't ask if it was an integer in the realm of infinite pure integers; he asked how to tell if a string was a number that could be converted to an int (presumably without loss). Andrew
