substr_compare
(PHP 5)
substr_compare — Binary safe comparison of two strings from an offset, up to length characters
Description
$main_str
, string $str
, int $offset
[, int $length
[, bool $case_insensitivity
= false
]] )
substr_compare() compares main_str
from position offset
with str
up to length
characters.
Parameters
-
main_str
-
The main string being compared.
-
str
-
The secondary string being compared.
-
offset
-
The start position for the comparison. If negative, it starts counting from the end of the string.
-
length
-
The length of the comparison. The default value is the largest of the length of the
str
compared to the length ofmain_str
less theoffset
. -
case_insensitivity
-
If
case_insensitivity
isTRUE
, comparison is case insensitive.
Return Values
Returns < 0 if main_str
from position
offset
is less than str
, >
0 if it is greater than str
, and 0 if they are equal.
If offset
is equal to or greater than the length of
main_str
or length
is set and
is less than 1, substr_compare() prints a warning and returns
FALSE
.
Changelog
Version | Description |
---|---|
5.1.0 |
Added the possibility to use a negative offset .
|
Examples
Example #1 A substr_compare() example
<?php
echo substr_compare("abcde", "bc", 1, 2); // 0
echo substr_compare("abcde", "de", -2, 2); // 0
echo substr_compare("abcde", "bcg", 1, 2); // 0
echo substr_compare("abcde", "BC", 1, 2, true); // 0
echo substr_compare("abcde", "bc", 1, 3); // 1
echo substr_compare("abcde", "cd", 1, 2); // -1
echo substr_compare("abcde", "abc", 5, 1); // warning
?>
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Коментарии
Take note of the `length` parameter: "The default value is the largest of the length of the str compared to the length of main_str less the offset."
This is *not* the length of str as you might (I always) expect, so if you leave it out, you'll get unexpected results. Example:
<?php
$hash = '$5$lalalalalalalala$crypt.output.here';
var_dump(substr_compare($hash, '$5$', 0)); # int(34)
var_dump(substr_compare($hash, '$5$', 0, 3)); # int(0)
var_dump(PHP_VERSION); # string(6) "5.3.14"
?>
When you came to this page, you may have been looking for something a little simpler: A function that can check if a small string exists within a larger string starting at a particular index. Using substr_compare() for this can leave your code messy, because you need to check that your string is long enough (to avoid the warning), manually specify the length of the short string, and like many of the string functions, perform an integer comparison to answer a true/false question.
I put together a simple function to return true if $str exists within $mainStr. If $loc is specified, the $str must begin at that index. If not, the entire $mainStr will be searched.
<?php
function contains_substr($mainStr, $str, $loc = false) {
if ($loc === false) return (strpos($mainStr, $str) !== false);
if (strlen($mainStr) < strlen($str)) return false;
if (($loc + strlen($str)) > strlen($mainStr)) return false;
return (strcmp(substr($mainStr, $loc, strlen($str)), $str) == 0);
}
?>
This function efficiently implements checks for strings beginning or ending with other strings:
<?php
function str_begins($haystack, $needle) {
return 0 === substr_compare($haystack, $needle, 0, strlen($needle));
}
function str_ends($haystack, $needle) {
return 0 === substr_compare($haystack, $needle, -strlen($needle));
}
var_dump(str_begins('http://example.com', 'https://'));
?>
Note that these are not multi-byte character set aware.