我如何编写两个函数,如果它以指定的字符/字符串开头或以指定的字符串结尾,那么它们将接受字符串并返回?
例如:
$str = '|apples}';
echo startsWith($str, '|'); //Returns true
echo endsWith($str, '}'); //Returns true
我如何编写两个函数,如果它以指定的字符/字符串开头或以指定的字符串结尾,那么它们将接受字符串并返回?
例如:
$str = '|apples}';
echo startsWith($str, '|'); //Returns true
echo endsWith($str, '}'); //Returns true
当前回答
如果速度对你很重要,试试这个。(我认为这是最快的方法)
仅适用于字符串,如果$haystack只有1个字符
function startsWithChar($needle, $haystack)
{
return ($needle === $haystack[0]);
}
function endsWithChar($needle, $haystack)
{
return ($needle === $haystack[strlen($haystack) - 1]);
}
$str='|apples}';
echo startsWithChar('|',$str); //Returns true
echo endsWithChar('}',$str); //Returns true
echo startsWithChar('=',$str); //Returns false
echo endsWithChar('#',$str); //Returns false
其他回答
这里有一个针对PHP4的有效解决方案。如果在PHP5上使用substra_compare而不是strcasecmp(substr(…)),可以获得更快的结果。
function stringBeginsWith($haystack, $beginning, $caseInsensitivity = false)
{
if ($caseInsensitivity)
return strncasecmp($haystack, $beginning, strlen($beginning)) === 0;
else
return strncmp($haystack, $beginning, strlen($beginning)) === 0;
}
function stringEndsWith($haystack, $ending, $caseInsensitivity = false)
{
if ($caseInsensitivity)
return strcasecmp(substr($haystack, strlen($haystack) - strlen($ending)), $haystack) === 0;
else
return strpos($haystack, $ending, strlen($haystack) - strlen($ending)) !== false;
}
我会这样做
function startWith($haystack,$needle){
if(substr($haystack,0, strlen($needle))===$needle)
return true;
}
function endWith($haystack,$needle){
if(substr($haystack, -strlen($needle))===$needle)
return true;
}
Fastest endsWith()解决方案:
# Checks if a string ends in a string
function endsWith($haystack, $needle) {
return substr($haystack,-strlen($needle))===$needle;
}
基准:
# This answer
function endsWith($haystack, $needle) {
return substr($haystack,-strlen($needle))===$needle;
}
# Accepted answer
function endsWith2($haystack, $needle) {
$length = strlen($needle);
return $length === 0 ||
(substr($haystack, -$length) === $needle);
}
# Second most-voted answer
function endsWith3($haystack, $needle) {
// search forward starting from end minus needle length characters
if ($needle === '') {
return true;
}
$diff = \strlen($haystack) - \strlen($needle);
return $diff >= 0 && strpos($haystack, $needle, $diff) !== false;
}
# Regex answer
function endsWith4($haystack, $needle) {
return preg_match('/' . preg_quote($needle, '/') . '$/', $haystack);
}
function timedebug() {
$test = 10000000;
$time1 = microtime(true);
for ($i=0; $i < $test; $i++) {
$tmp = endsWith('TestShortcode', 'Shortcode');
}
$time2 = microtime(true);
$result1 = $time2 - $time1;
for ($i=0; $i < $test; $i++) {
$tmp = endsWith2('TestShortcode', 'Shortcode');
}
$time3 = microtime(true);
$result2 = $time3 - $time2;
for ($i=0; $i < $test; $i++) {
$tmp = endsWith3('TestShortcode', 'Shortcode');
}
$time4 = microtime(true);
$result3 = $time4 - $time3;
for ($i=0; $i < $test; $i++) {
$tmp = endsWith4('TestShortcode', 'Shortcode');
}
$time5 = microtime(true);
$result4 = $time5 - $time4;
echo $test.'x endsWith: '.$result1.' seconds # This answer<br>';
echo $test.'x endsWith2: '.$result4.' seconds # Accepted answer<br>';
echo $test.'x endsWith3: '.$result2.' seconds # Second most voted answer<br>';
echo $test.'x endsWith4: '.$result3.' seconds # Regex answer<br>';
exit;
}
timedebug();
基准结果:
10000000x endsWith: 1.5760900974274 seconds # This answer
10000000x endsWith2: 3.7102129459381 seconds # Accepted answer
10000000x endsWith3: 1.8731069564819 seconds # Second most voted answer
10000000x endsWith4: 2.1521229743958 seconds # Regex answer
简短易懂的一行,没有正则表达式。
startsWith()是直接向前的。
function startsWith($haystack, $needle) {
return (strpos($haystack, $needle) === 0);
}
endsWith()使用稍微花哨且缓慢的strrev():
function endsWith($haystack, $needle) {
return (strpos(strrev($haystack), strrev($needle)) === 0);
}
最近,我通常使用下划线php这样的库。
require_once("vendor/autoload.php"); //use if needed
use Underscore\Types\String;
$str = "there is a string";
echo( String::startsWith($str, 'the') ); // 1
echo( String::endsWith($str, 'ring')); // 1
图书馆里还有很多其他方便的功能。