startsWith()和endsWith()函数在PHP中
我该如何编写两个函数,如果它以指定的字符/字符串开头或者以它结束,则返回一个字符串并返回?
例如:
$str = '|apples}';
echo startsWith($str, '|'); //Returns true
echo endsWith($str, '}'); //Returns true
function startsWith($haystack, $needle)
{
$length = strlen($needle);
return (substr($haystack, 0, $length) === $needle);
}
function endsWith($haystack, $needle)
{
$length = strlen($needle);
return $length === 0 ||
(substr($haystack, -$length) === $needle);
}
如果你不想使用正则表达式,请使用它。
可以分别使用strrpos
和strpos
来检查start-with和ends。
请注意,使用strrpos
来检查开始与strpos
来检查结束将尽快返回而不是检查整个字符串直到结束。 此外,此解决方案不会创建临时字符串。 考虑解释之前的原因downvoting。 仅仅因为DWTF的f-wit不明白这个函数是如何工作的,或者认为只有一个解决方案并不意味着这个答案是错误的。
function startsWith($haystack, $needle) {
// search backwards starting from haystack length characters from the end
return $needle === "" || strrpos($haystack, $needle, -strlen($haystack)) !== false;
}
function endsWith($haystack, $needle) {
// search forward starting from end minus needle length characters
return $needle === "" || (($temp = strlen($haystack) - strlen($needle)) >= 0 && strpos($haystack, $needle, $temp) !== false);
}
测试和结果(与此相比较):
startsWith("abcdef", "ab") -> true
startsWith("abcdef", "cd") -> false
startsWith("abcdef", "ef") -> false
startsWith("abcdef", "") -> true
startsWith("", "abcdef") -> false
endsWith("abcdef", "ab") -> false
endsWith("abcdef", "cd") -> false
endsWith("abcdef", "ef") -> true
endsWith("abcdef", "") -> true
endsWith("", "abcdef") -> false
注意: strncmp
和substr_compare
函数将胜过此函数。
2016年8月23日更新
功能
function substr_startswith($haystack, $needle) {
return substr($haystack, 0, strlen($needle)) === $needle;
}
function preg_match_startswith($haystack, $needle) {
return preg_match('~' . preg_quote($needle, '~') . '~A', $haystack) > 0;
}
function substr_compare_startswith($haystack, $needle) {
return substr_compare($haystack, $needle, 0, strlen($needle)) === 0;
}
function strpos_startswith($haystack, $needle) {
return strpos($haystack, $needle) === 0;
}
function strncmp_startswith($haystack, $needle) {
return strncmp($haystack, $needle, strlen($needle)) === 0;
}
function strncmp_startswith2($haystack, $needle) {
return $haystack[0] === $needle[0]
? strncmp($haystack, $needle, strlen($needle)) === 0
: false;
}
测试
echo 'generating tests';
for($i = 0; $i < 100000; ++$i) {
if($i % 2500 === 0) echo '.';
$test_cases[] = [
random_bytes(random_int(1, 7000)),
random_bytes(random_int(1, 3000)),
];
}
echo "done!n";
$functions = ['substr_startswith', 'preg_match_startswith', 'substr_compare_startswith', 'strpos_startswith', 'strncmp_startswith', 'strncmp_startswith2'];
$results = [];
foreach($functions as $func) {
$start = microtime(true);
foreach($test_cases as $tc) {
$func(...$tc);
}
$results[$func] = (microtime(true) - $start) * 1000;
}
asort($results);
foreach($results as $func => $time) {
echo "$func: " . number_format($time, 1) . " msn";
}
结果(PHP 7.0.9)
(排序最快到最慢)
strncmp_startswith2: 40.2 ms
strncmp_startswith: 42.9 ms
substr_compare_startswith: 44.5 ms
substr_startswith: 48.4 ms
strpos_startswith: 138.7 ms
preg_match_startswith: 13,152.4 ms
结果(PHP 5.3.29)
(排序最快到最慢)
strncmp_startswith2: 477.9 ms
strpos_startswith: 522.1 ms
strncmp_startswith: 617.1 ms
substr_compare_startswith: 706.7 ms
substr_startswith: 756.8 ms
preg_match_startswith: 10,200.0 ms
startswith_benchmark.php
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