On Sat, Mar 16, 2013 at 12:21 PM, Ashley Sheridan <ash@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Sat, 2013-03-16 at 11:46 -0400, Andrew Ballard wrote: > > 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 > > > Ah, I see. I think that's not an issue as such with regular expressions > having problems, more that bit limitations has a problem with numbers! ANY computer system is going to have limitations with numbers -- you can't store infinity in a finite system. LOL > Bearing that in mind, this does the trick: > > $string1 = '999999999'; > $string2 = '9999999999'; > $string3 = '999999999999999999999999999999'; > > var_dump($string === (intval($string1).'')); > var_dump($string === (intval($string2).'')); > var_dump($string === (intval($string3).'')); That's the same thing I posted, just different syntax. You are still converting the string to an int, converting the int back to a string, and comparing the resulting value to the original string using the identical (===) operator. Depending on one's needs, it could be tweaked a little to handle leading/trailing spaces, leading zeroes, etc. function is_int_hiding_as_string($value) { if (is_string($value)) { // remove any spaces around the value. $value = trim($value); // check for a sign :-) $sign = (substr($value, 0, 1) === '-') ? '-' : ''; // strip off the sign, any additional leading spaces or zeroes $value = ltrim($value, ' 0-'); // I didn't strip off trailing zeroes after the decimal because // I consider that a loss of precision, but you could do so // if necessary. return ($value === $sign . (int)$value); } return false; } > I'm getting the expected results on my machine (32-bit) but a 64-bit machine would get the correct results for larger numbers. As I understood the original post, these ARE the correct results on ANY system. If the string value can be safely converted to an int *in the environment under which the script is executing* without loss of precision, this will return true; if it cannot, it returns false. Sorry for getting carried away, but it is SO much easier to respond on an actual keyboard than my phone. :-) Andrew -- PHP General Mailing List (http://www.php.net/) To unsubscribe, visit: http://www.php.net/unsub.php
