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preg_match_all returns false for first match

Posted on 2010-11-28
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Last Modified: 2012-05-10
I am writing a calculator engine, and need to get the numbers and operators from the expression (a string). To do this I am using preg_match_all, with PREG_OFFSET_CAPTURE, that returns an array with all of the numbers and another with the operators. The operators part works fine, but the first matched number in the array is false instead of the number. Here is the function I am using:

$exp='13+4x2';
preg_match_all('/[0-9.\-\[]+/',$exp,$exp_nums,PREG_OFFSET_CAPTURE);

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this returns:

array(1) {
  [0]=>
  array(3) {
    [0]=>
    array(2) {
      [0]=>
      bool(false) //improper value
      [1]=>
      int(1)
    }
    [1]=>
    array(2) {
      [0]=>
      string(1) "4"
      [1]=>
      int(4)
    }
    [2]=>
    array(2) {
      [0]=>
      string(1) "2"
      [1]=>
      int(6)
    }
  }
}

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Does anyone know how to fix this
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Question by:cloud-9
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6 Comments
 
LVL 35

Accepted Solution

by:
Terry Woods earned 500 total points
ID: 34227650
How about this: (results below)

$exp='13+4x2';
preg_match_all('/[0-9.]+/','#'.$exp,$exp_nums,PREG_OFFSET_CAPTURE);
print_r($exp_nums);
Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [0] => 13
                    [1] => 1
                )

            [1] => Array
                (
                    [0] => 4
                    [1] => 4
                )

            [2] => Array
                (
                    [0] => 2
                    [1] => 6
                )

        )

)

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0
 
LVL 35

Expert Comment

by:Terry Woods
ID: 34227655
Your code gives me this result actually, which seems different from what you're getting:
Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [0] => 13
                    [1] => 0
                )

            [1] => Array
                (
                    [0] => 4
                    [1] => 3
                )

            [2] => Array
                (
                    [0] => 2
                    [1] => 5
                )

        )

)

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0
 
LVL 35

Expert Comment

by:Terry Woods
ID: 34227662
I'm not sure why you're trying to match - and [ characters in your pattern:
/[0-9.\-\[]+/

 but the backslashes need to have an extra escape character if you're going to try to do it:
/[0-9.\\-\\[]+/

However, with the code:
$exp='13+4x2-5-17';
preg_match_all('/[0-9.\\-\\[]+/',$exp,$exp_nums,PREG_OFFSET_CAPTURE);
print_r($exp_nums);

The result is probably not what you want:


Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [0] => 13
                    [1] => 0
                )

            [1] => Array
                (
                    [0] => 4
                    [1] => 3
                )

            [2] => Array
                (
                    [0] => 2-5-17
                    [1] => 5
                )

        )

)

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LVL 35

Expert Comment

by:Terry Woods
ID: 34227663
(My first suggestion solves that problem)
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LVL 3

Assisted Solution

by:cloud-9
cloud-9 earned 0 total points
ID: 34235119
The - and ] characters denote a negative sign (a subtraction operator is _) and a fraction symbol such as on a scientific calculator (ex 2[5 means two fifths). "2-5-17" would  produce a syntax error on my calculator. But all of this is beside the point.

I discovered my error: I am using gmp_init to convert all of the numbers in the array. I forgot I was using a different array structure previously, and I was trying to convert an array into a gmp number. Apparently the failure of the first gmp_init broke the loop and the other values were not processed. The array I was var_dumping came after the failed gmp_init. So there was no problem with preg_match_all in the first place. Sorry for inconvenience.
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LVL 3

Author Closing Comment

by:cloud-9
ID: 34272890
I am still giving points for the prompt response.
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