Php, difference between \d and [\d]

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August 20th, 2008, 04:33 AM

srisa

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Php, difference between \d and [\d]

Hello,
I have this regex to check for the existence of digits in a given string. It may or may not contain anything else, but is should have one or more digits.
Here is the code

php Code:

Original - php Code
if (preg_match('/\d+/', $val)) echo "$val contains digits\n"; else echo "$val does not contain digits\n";

 if (preg_match('/\d+/', $val))
    echo "$val contains digits\n";
else
    echo "$val does not contain digits\n";

php Code:

Original - php Code
if (preg_match('/[\d]+/', $val)) echo "$val contains digits\n"; else echo "$val does not contain digits\n";

 if (preg_match('/[\d]+/', $val))
    echo "$val contains digits\n";
else
    echo "$val does not contain digits\n";

Both code snippets give same results. So, what is the difference between \d and [\d].

Thank you.

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August 20th, 2008, 05:03 AM

ishnid

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There's no difference. Using [ ... ] allows you to create a character class which will match any of the characters contained within it. So for example if you wanted to match 'a', 'b' or 'c', you'd do:

Code:

[abc]

There are also pre-created character classes (\w for 'word characters', \d for digits, etc). So these two are equivalent:

Code:

[0123456789]
\d

Your square bracket character classes can contain these predefined ones too, so if for example you wanted to match numeric digits or whitespace, you could do:

Code:

[\d\s]

Here, because you're only using one predefined character class, the square brackets are unnecessary.

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August 20th, 2008, 05:34 AM

srisa

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Thanks.
Some notes for you:
I repped you but the message is not visible. When I tried to rep you again it said, 'You cannot rep the same post twice'.
It would be better if the resources and suggestions threads are stickied. Otherwise they will be go into the last page.

Php, difference between \d and [\d]

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