Get "at most" last n characters from string using PHP substr?

Question

Answer of this question:

How can I get the last 7 characters of a PHP string? - Stack Overflow How can I get the last 7 characters of a PHP string?

shows this statement:

substr($s, -7)

However, if length of $s is smaller than 7, it will return empty string(tested on PHP 5.2.6), e.g.

substr("abcd", -4) returns "abcd"
substr("bcd", -4) returns nothing

Currently, my workaround is

trim(substr("   $s",-4)) // prepend 3 blanks

Is there another elegant way to write substr() so it can be more perfect?

====

EDIT: Sorry for the typo of return value of substr("bcd", -4) in my post. It misguides people here. It should return nothing. I already correct it. (@ 2016/1/29 17:03 GMT+8)

I jst wish when I want to get last 4 but if there's not enough characters, the whole string will be return, i.e. what I write in the title "at most", not "exactly". — Scott Chu, Jan 29 '16 at 08:29
@ScottChu `substr("bcd", -4)` returns the whole string **bcd**. whats not working really? — jameshwart lopez, Jan 29 '16 at 08:31
I see axiac's answer. It's a bug. Thanks for each one of you who answered and commented. — Scott Chu, Jan 29 '16 at 08:59
do you mean sth like this `strlen($str) > 4 ? substr($str, -4) : $str;` ? — Andrew, Jan 29 '16 at 09:06

axiac · Accepted Answer · 2016-01-29T08:42:43.403

substr("abcd", -4) returns "abcd"
substr("bcd", -4) returns "bcd"

This is the correct behaviour of substr().

There was a bug in the substr() function in PHP versions 5.2.2-5.2.6 that made it return FALSE when its first argument (start) was negative and its absolute value was larger than the length of the string.

The behaviour is documented.

You should upgrade your PHP to a newer version (5.6 or 7.0). PHP 5.2 is dead and buried more than 5 years ago.

Or, at least, upgrade PHP 5.2 to its latest release (5.2.17)

An elegant solution to your request (assuming you are locked with a faulty PHP version):

function substr52($string, $start, $length)
{
    $l = strlen($string);
    // Clamp $start and $length to the range [-$l, $l]
    // to circumvent the faulty behaviour in PHP 5.2.2-5.2.6
    $start  = min(max($start, -$l), $l);
    $length = min(max($start, -$l), $l);

    return substr($string, $start, $length);
}

However, it doesn't handle the cases when $length is 0, FALSE, NULL or when it is omitted.

score 0 · Answer 2 · answered Jan 29 '16 at 08:41

0

In my haste with first comment I missed a parameter - I think it should have been more like this.

$s = 'look at all the thingymajigs';
echo trim( substr( $s, ( strlen( $s ) >= 7 ? -7 : -strlen( $s ) ), strlen( $s ) ) );

answered Jan 29 '16 at 08:41

Professor Abronsius

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Get "at most" last n characters from string using PHP substr?

2 Answers2