How to find the place of digits in a string in PHP

Question

I want to find the place of a digit-based substring in a string as

$str = " test No. 82 and No. 8 more No. 234";
$needle = "No. 8";

I tried strpos as

$index = stripos($str,$needle);

but it finds No. 82 instead of No. 8.

Is the simplest way to use preg_match with PREG_OFFSET_CAPTURE? Does it really necessarily regex?

Why do you need the indices? A regex can do more than just return the indices. What is the final ideal result? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Oct 26, 2016 at 11:02
what does the place of digits mean? the left position(index) of each number OR should it be a range with (left boundary, right boundary) for each matched item? — RomanPerekhrest
– RomanPerekhrest, Commented Oct 26, 2016 at 11:02
@WiktorStribiżew I use it as an offset in another strpos to find a substring after the digits. — Googlebot
– Googlebot, Commented Oct 26, 2016 at 11:12
Is that an XY problem then? What is the real text you need to get from the above string? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Oct 26, 2016 at 11:13

RomanPerekhrest · Accepted Answer · 2016-10-26 11:20:45Z

3

"Regex" approach would be preferable for such complex cases, preg_match_all function will do the job:

$str = " test No. 82 and No. 8 more No. 234";
preg_match_all("/No\.\s+\d+\b/", $str, $matches, PREG_OFFSET_CAPTURE);

print_r($matches[0]);

According to your additional condition with search $needle:
- we should consider the right boundary of the search "needle" by using metacharacter \b

$str = " test No. 82 and No. 8 more No. 234";
$needle = "No. 8";
preg_match_all("/$needle\b/", $str, $matches, PREG_OFFSET_CAPTURE);

print_r($matches[0]);

The output:

Array
(
    [0] => Array
        (
            [0] => No. 8
            [1] => 17
        )
)

edited Oct 26, 2016 at 11:20

answered Oct 26, 2016 at 11:12

RomanPerekhrest

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Comments

arkascha · Accepted Answer · 2016-10-26 11:07:59Z

You will need a regular expression to match the precise sequence pattern. I suggest this apporach:

<?php
$subject = " test No. 82 and No. 8 more No. 234";
$pattern = '/No\. \d+/';
$offset = 0;
while (preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, $offset+1)) {
    $offset = $matches[0][1];
    var_dump($matches);
}

The output, which of course can be further processed, is:

array(1) {
  [0] =>
  array(2) {
    [0] =>
    string(6) "No. 82"
    [1] =>
    int(6)
  }
}
array(1) {
  [0] =>
  array(2) {
    [0] =>
    string(5) "No. 8"
    [1] =>
    int(17)
  }
}
array(1) {
  [0] =>
  array(2) {
    [0] =>
    string(7) "No. 234"
    [1] =>
    int(28)
  }
}

Depending on your exact requirements you may want to modify the pattern to '/No\. (\d+)/' to match exactly the numeric parts. You also will have to adapt the offset line to $offset = $matches[1][1]; then obviously.

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