PHP中的正则表达式“不匹配数字”

Question

I would like to check if a string is in another string with comma separated. I've write some code and it work like this...

$find_number = '3'
$string_to_search = '1,3,124,12'
preg_match('/[^0-9]'.$find_number.'[^0-9]/', string_to_search);
//match

$find_number = '4'
$string_to_search = '1,3,124,12'
preg_match('/[^0-9]'.$find_number.'[^0-9]/', string_to_search);
//not match

Which is what I expected. The problem is that the first and last string can't recognized in this expression. What did I do wrong?

Answer 1

You need to make sure to check if there are no digits on both sides of the $find_number, and that is why you need (?<!\d) / (?!\d) lookarounds that do not consume text before and after the number you need to match allowing to check the first and last items. The [^0-9] in your pattern are negated character class instances, that require a character other than a digit before and after the find_number. The lookarounds will just fail the match if there is a digit before ((?<!\d) negative lookbehind) or after (with (?!\d) negative lookahead) the find_number. See below:

$find_number = '3';
$string_to_search = '1,3,124,12';
if (preg_match('/(?<!\d)'.$find_number.'(?!\d)/', $string_to_search)) {
    echo "match!";
}

See the PHP demo.

An alternative is to use explode with in_array:

$find_number = '3';
$string_to_search = '1,3,124,12';
if (in_array($find_number, explode(",", $string_to_search))) {
    echo "match!";
}

See another PHP demo