Edit report at https://bugs.php.net/bug.php?id=73913&edit=1
ID: 73913
Comment by: dima at virtuman dot com
Reported by: proartex at mail dot ru
Summary: broken strrpos with negative offset
Status: Assigned
Type: Bug
Package: Strings related
Operating System: macOS Sierra 10.12.1
PHP Version: 5.6.29
Assigned To: heiglandreas
Block user comment: N
Private report: N
New Comment:
my previous comment is not absolutely right. I'm not sure why those conditions are needed:
if (needle_len > -offset) {
e = haystack + haystack_len - needle_len;
} else {
e = haystack + haystack_len + offset;
}
In all cases we need to subtract absolute value of offset from e pointer and also subtract value of
needle length. There is no reason to check needle_len > -offset
Previous Comments:
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[2017-01-12 10:33:07] dima at virtuman dot com
Looks like the problem is related to https://github.com/php/php-src/blob/PHP-5.6.29/ext/standard/string.c#L1987
replace this one:
e = haystack + haystack_len + offset;
with this one:
e = haystack + haystack_len + offset - needle_len;
will solve the problem.
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[2017-01-11 21:57:27] heiglandreas@php.net
Looks like you're right! I dug deeper into it and it seems there is an issue when the negative
offset is smaller or equals the size of the needle.
I'm digging deeper into it.
------------------------------------------------------------------------
[2017-01-11 18:03:34] proartex at mail dot ru
1. Does strrpos("works_like_a_charm", 'charm', 15) really equals to
strrpos("works_like_a_charm", 'charm', -3)? false != 13. It is also applicable
for 3 last cases.
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[2017-01-11 17:32:03] heiglandreas@php.net
when offset is negative the search *starts* that many characters *from the end*. The search is not
excluding the last n characters.
strrpos("aaaa", 'aa', -2) == strrpos("aaaa", 'aa', 2)
strrpos("aaaa", 'a', -1) == strrpos("aaaa", 'a', 3)
strrpos("/documents/show/5474", '/', -20) ==
strrpos("/documents/show/5474", '/', 0)
strrpos("works_like_a_charm", 'charm', -3) ==
strrpos("works_like_a_charm", 'charm', 15)
strrpos("works_like_a_charm", 'charm', -4) ==
strrpos("works_like_a_charm", 'charm', 14)
So they work as expected.
What you want to do would be achieved by this:
strrpos(substr("aaaa", -2), "aa");
When needle is longer than the remaining string, the offset seems to be expanded to at least include
the needle.
Note also the comment on http://php.net/manual/de/function.strrpos.php#76447
------------------------------------------------------------------------
[2017-01-11 17:19:23] proartex at mail dot ru
last case must be var_dump(strrpos("works_like_a_charm", 'charm', -5)); //ER:
false, AR: 13
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