Why does substr not return undef at the end of a string?

perl, substr

Solution

substr($string, length($string), 1)

This gave you an empty string because, `substr` considers the `offset` between `0 to len(str)`, and anything beyond that range is `undef`.

So, `substr("aa", 2, 1);` -> will give you the empty string after last `a` and,`substr("aa", 3, 1);` -> Will give you `undef` (Substring completely outside range)

Similarly: -

- `substr("aa", 2, 2);` -> Will give you the empty string after last `a` (Substring partly outside the range)

Now, for the second one: -

substr($string, length($string) + 1, 1)

This is already past the last allowed `offset`. So it returns `undef` value.

Suppose: -

$str = "abcd";

Then, the index will look like: -

  a   b   c   d             undef
0   1   2   3  len(str)  len(str) + 1

UPDATE: -

So, as @Borodin explained in his post, the character `d` comes between the offsets - `3` and `len(str)` in the above example.

But, if we try to access anything beyond `len(str)` including `len(str)`, we will get an `empty` string, as in the documentation, which says that -

If OFFSET and LENGTH specify a substring that is partly outside the string, only the part within the string is returned.

Also, if we try to access anything beyond `len(str)` excluding the `len(str)`, we will get `undef` value, as in docs: -

If the substring is beyond either end of the string, substr() returns the undefined value and produces a warning.

Problem

Original source