PHP: substr_compare - Manual (original) (raw)
(PHP 5, PHP 7, PHP 8)
substr_compare — Binary safe comparison of two strings from an offset, up to length characters
Description
Parameters
haystack
The main string being compared.
needle
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 needle compared to the length ofhaystack minus theoffset.
case_insensitive
If case_insensitive is [true](reserved.constants.php#constant.true), comparison is case insensitive.
Return Values
Returns a value less than 0 if string1 is less than string2; a value greater than 0 if string1 is greater thanstring2, and 0 if they are equal. No particular meaning can be reliably inferred from the value aside from its sign.
If offset is equal to (prior to PHP 7.2.18, 7.3.5) or greater than the length of haystack, or thelength is set and is less than 0,substr_compare() prints a warning and returns**[false](reserved.constants.php#constant.false)**.
Changelog
| Version | Description |
|---|---|
| 8.2.0 | This function is no longer guaranteed to returnstrlen($string1) - strlen($string2) when string lengths are not equal, but may now return -1 or1 instead. |
| 8.0.0 | length is nullable now. |
| 7.2.18, 7.3.5 | offset may now be equal to the length of haystack. |
Examples
Example #1 A substr_compare() example
<?php echo substr_compare("abcde", "bc", 1, 2), PHP_EOL; // 0 echo substr_compare("abcde", "de", -2, 2), PHP_EOL; // 0 echo substr_compare("abcde", "bcg", 1, 2), PHP_EOL; // 0 echo substr_compare("abcde", "BC", 1, 2, true), PHP_EOL; // 0 echo substr_compare("abcde", "bc", 1, 3), PHP_EOL; // 1 echo substr_compare("abcde", "cd", 1, 2), PHP_EOL; // -1 echo substr_compare("abcde", "abc", 5, 1), PHP_EOL; // -1 ?>
See Also
- strncmp() - Binary safe string comparison of the first n characters
Found A Problem?
13 years ago
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 <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>s</mi><mi>t</mi><mi>r</mi><mi>e</mi><mi>x</mi><mi>i</mi><mi>s</mi><mi>t</mi><mi>s</mi><mi>w</mi><mi>i</mi><mi>t</mi><mi>h</mi><mi>i</mi><mi>n</mi></mrow><annotation encoding="application/x-tex">str exists within </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">s</span><span class="mord mathnormal">t</span><span class="mord mathnormal">re</span><span class="mord mathnormal">x</span><span class="mord mathnormal">i</span><span class="mord mathnormal">s</span><span class="mord mathnormal">t</span><span class="mord mathnormal">s</span><span class="mord mathnormal" style="margin-right:0.02691em;">w</span><span class="mord mathnormal">i</span><span class="mord mathnormal">t</span><span class="mord mathnormal">hin</span></span></span></span>mainStr. If <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>o</mi><mi>c</mi><mi>i</mi><mi>s</mi><mi>s</mi><mi>p</mi><mi>e</mi><mi>c</mi><mi>i</mi><mi>f</mi><mi>i</mi><mi>e</mi><mi>d</mi><mo separator="true">,</mo><mi>t</mi><mi>h</mi><mi>e</mi></mrow><annotation encoding="application/x-tex">loc is specified, the </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">oc</span><span class="mord mathnormal">i</span><span class="mord mathnormal">ss</span><span class="mord mathnormal">p</span><span class="mord mathnormal">ec</span><span class="mord mathnormal">i</span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal">i</span><span class="mord mathnormal">e</span><span class="mord mathnormal">d</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">h</span><span class="mord mathnormal">e</span></span></span></span>str must begin at that index. If not, the entire $mainStr will be searched.
<?php
function contains_substr($mainStr, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>s</mi><mi>t</mi><mi>r</mi><mo separator="true">,</mo></mrow><annotation encoding="application/x-tex">str, </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8095em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">s</span><span class="mord mathnormal">t</span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mpunct">,</span></span></span></span>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, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>o</mi><mi>c</mi><mo separator="true">,</mo><mi>s</mi><mi>t</mi><mi>r</mi><mi>l</mi><mi>e</mi><mi>n</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">loc, strlen(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">oc</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">s</span><span class="mord mathnormal">t</span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mopen">(</span></span></span></span>str)), $str) == 0);
}
?>9 years ago
This function efficiently implements checks for strings beginning or ending with other strings:
<?php
function str_begins($haystack, $needle) {
return 0 === substr_compare($haystack, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>n</mi><mi>e</mi><mi>e</mi><mi>d</mi><mi>l</mi><mi>e</mi><mo separator="true">,</mo><mn>0</mn><mo separator="true">,</mo><mi>s</mi><mi>t</mi><mi>r</mi><mi>l</mi><mi>e</mi><mi>n</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">needle, 0, strlen(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">n</span><span class="mord mathnormal">ee</span><span class="mord mathnormal">d</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord">0</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">s</span><span class="mord mathnormal">t</span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mopen">(</span></span></span></span>needle));
}
function str_ends($haystack, $needle) {
return 0 === substr_compare($haystack, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>n</mi><mi>e</mi><mi>e</mi><mi>d</mi><mi>l</mi><mi>e</mi><mo separator="true">,</mo><mo>−</mo><mi>s</mi><mi>t</mi><mi>r</mi><mi>l</mi><mi>e</mi><mi>n</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">needle, -strlen(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">n</span><span class="mord mathnormal">ee</span><span class="mord mathnormal">d</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord">−</span><span class="mord mathnormal">s</span><span class="mord mathnormal">t</span><span class="mord mathnormal" style="margin-right:0.02778em;">r</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mopen">(</span></span></span></span>needle));
}
var_dump(str_begins('http://example.com', 'https://'));
?>
Note that these are not multi-byte character set aware.13 years ago
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 <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>h</mi><mi>a</mi><mi>s</mi><mi>h</mi><msup><mo>=</mo><mo mathvariant="normal" lspace="0em" rspace="0em">′</mo></msup></mrow><annotation encoding="application/x-tex">hash = '</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7519em;"></span><span class="mord mathnormal">ha</span><span class="mord mathnormal">s</span><span class="mord mathnormal">h</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"><span class="mrel">=</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.7519em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mtight">′</span></span></span></span></span></span></span></span></span></span></span></span>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"
?>