PHP prepend leading zero before single digit number, on-the-fly

Question

PHP - Is there a quick, on-the-fly method to test for a single character string, then prepend a leading zero?

Example:

$year = 11;
$month = 4;

$stamp = $year.add_single_zero_if_needed($month);  // Imaginary function

echo $stamp; // 1104

After testing, turns out sprintf() was a bit better: it has a common language format and doesn't use a class constant, among other things. — Ben, Jan 15 '13 at 07:09

Kirk Beard · Accepted Answer · 2016-02-25T09:53:19.170

603

You can use sprintf: http://php.net/manual/en/function.sprintf.php

<?php
$num = 4;
$num_padded = sprintf("%02d", $num);
echo $num_padded; // returns 04
?>

It will only add the zero if it's less than the required number of characters.

Edit: As pointed out by @FelipeAls:

When working with numbers, you should use %d (rather than %s), especially when there is the potential for negative numbers. If you're only using positive numbers, either option works fine.

For example:

sprintf("%04s", 10); returns 0010
sprintf("%04s", -10); returns 0-10

Where as:

sprintf("%04d", 10); returns 0010
sprintf("%04d", -10); returns -010

edited Feb 25 '16 at 09:53

answered Apr 14 '11 at 05:50

Kirk Beard

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Beware of negative numbers (obviously not a problem with dates here! :) ). `%03s` can output `0-5` where `%03d` would output `-05` – FelipeAls Jul 11 '14 at 09:09
this doesn't work with negative numbers – Rafik Bari Feb 17 '15 at 19:39
@RafikBari I've updated my answer to include the information @FelipeAls mentioned. Negative numbers are handled fine, provided you use `%02d`. – Kirk Beard Feb 17 '15 at 19:53
2

Your edit is wrong, sprintf("%04s", 10); returns 0010, not 1000. – Marek Lisý Oct 27 '15 at 18:40
1

Also sprintf("%04d", -10); returns -010. Tested on PHP 5.5.18 – Marek Lisý Oct 27 '15 at 18:42
Can this be reversed? – MichaelTheDev May 18 '22 at 09:38

score 230 · Answer 2 · edited Apr 15 '14 at 07:00

230

You can use str_pad for adding 0's

str_pad($month, 2, '0', STR_PAD_LEFT);

string str_pad ( string $input , int $pad_length [, string $pad_string = " " [, int $pad_type = STR_PAD_RIGHT ]] )

edited Apr 15 '14 at 07:00

likeitlikeit

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answered Apr 14 '11 at 05:46

Gaurav

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Pure gold right here! – Jordan Jul 27 '13 at 22:28
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@zzlalani - actually if you look carefully at the example in Kirk Beard's answer, it is saved to a variable :) – Ben Sep 14 '13 at 07:42
this doesn't work with negative nums – Rafik Bari Feb 17 '15 at 19:35

score 18 · Answer 3 · answered Apr 14 '11 at 05:50

18

The universal tool for string formatting, sprintf:

$stamp = sprintf('%s%02s', $year, $month);

http://php.net/manual/en/function.sprintf.php

answered Apr 14 '11 at 05:50

deceze

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str_pad is more readable. I like keeping things simple. sprintf is great function, i use it a lot for transaltions, when there must be a variable in the middle of the string, but for such thing, i will go with str_pad(); while i'm working only with positive integers. they don't require any fancy stuff. – Lukas Liesis Apr 04 '15 at 21:49
Use sprintf: sprintf('%08d', 1234567); Alternatively you can also use str_pad: str_pad($value, 8, '0', STR_PAD_LEFT); – Kamlesh Sep 04 '19 at 16:32
what about signed digit ? str_replace("00", "0", sprintf('%03d', $num)) – Sahib Khan Jun 05 '20 at 06:19

PHP prepend leading zero before single digit number, on-the-fly

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