How to extract substring by start-index and end-index?

Question

$str = 'HelloWorld';
$sub = substr($str, 3, 5);
echo $sub; // prints "loWor"

I know that substr() takes the first parameter, 2nd parameter is start index, while 3rd parameter is substring length to extract. What I need is to extract substring by startIndex and endIndex. What I need is something like this:

$str = 'HelloWorld';
$sub = my_substr_function($str, 3, 5);
echo $sub; // prints "lo"

Is there a function that does that in php? Or can you help me with a workaround solution, please?

Socio

while the "workaround solution" is trivial, this is actually a good question, as most programming languages do have the two versions of the substring extraction function (usually horribly named "substr" and "substring") one with the length parameter and the other with the end-index parameter. It seems it's not the case of PHP. – Orabelle

I wish PHP had this, like Javascript's substring. It's the little things like this that annoy me. – Breezy

Answer 1

It's just math

$sub = substr($str, 3, 5 - 3);

The length is the end minus the start.

Alden

i.e. There isn't a builtin PHP function to do so; you should use substr(). – Borreri

Answer 2

function my_substr_function($str, $start, $end)
{
  return substr($str, $start, $end - $start);
}

If you need to have it multibyte safe (i.e. for chinese characters, ...) use the mb_substr function:

function my_substr_function($str, $start, $end)
{
  return mb_substr($str, $start, $end - $start);
}

Historied

I think It's more general and better answer than accepted one. – Branscum

Shouldn't the inside substr(...) be mb_substr(...) - just in case..? – Donaldson

Well, most of us probably don't deal with multibyte characters ... but yes, it does make sense and is valid comment (I extended my answer with your suggestion). Thanks, +1! – Historied

Answer 3

Just subtract the start index from the end index and you have the length the function wants.

$start_index = 3;
$end_index = 5;
$sub = substr($str, $start_index, $end_index - $start_index);

Fibrinolysis

Answer 4

You can just use a negative value on the third parameter:

echo substr('HelloWorld', 3, -5);
// will print "lo"

If length is given and is negative, then that many characters will be omitted from the end of string (after the start position has been calculated when a start is negative).

As stated at the substr documentation.

Investment

Answer 5

Not exactly...

If we have a start index as 0, and we want JUST the first char, it becomes difficult as this will not output what you want. So if your code is requiring an $end_index:

// We want just the first char only.
$start_index = 0;
$end_index = 0;
echo $str[$end_index - $start_index]; // One way... or...
if($end_index == 0) ++$end_index;
$sub = substr($str, $start_index, $end_index - $start_index);
echo $sub; // The other way.

Micron

There @evilReiko, now you can see how substr() can be slightly more tricky. – Micron

if I want only the first character, I'll use substr($str, 0, 1 - 0); I don't see anything tricky or complicated – Socio

The "tricky" part I was referring to was that if you have an end index that is 0 or less than the start index, you will have unexpected results. One way of ridding yourself of this problem is by the answer stated above. Your comment, 'if I want only the first...' tells me that you are in full control of the start and end index variables. If you give this control to a program, however, you could have a start variable and end variable such as $start_index = 0; $end_index = 0; or $start_index = 0; $end_index = -10;. You have to be careful on what controls these $variables. Thus the trickiness – Micron