使用PHP substr从字符串中获取“最多”最后n个字符？

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), eg

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?

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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)

Answer 1

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)

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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.

Answer 2

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 ) ) );