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($str, '}'); //Returns true
当前回答
还可以使用正则表达式:
function endsWith($haystack, $needle, $case=true) {
return preg_match("/.*{$needle}$/" . (($case) ? "" : "i"), $haystack);
}
其他回答
为什么不采取以下措施?
//How to check if a string begins with another string
$haystack = "valuehaystack";
$needle = "value";
if (strpos($haystack, $needle) === 0){
echo "Found " . $needle . " at the beginning of " . $haystack . "!";
}
输出:
在valuehaystack的开头找到值!
请记住,如果在干草堆中没有找到针,strpos将返回false,如果且仅当在索引0处找到针时(即开头),strpos将返回0。
以下是结尾:
$haystack = "valuehaystack";
$needle = "haystack";
//If index of the needle plus the length of the needle is the same length as the entire haystack.
if (strpos($haystack, $needle) + strlen($needle) === strlen($haystack)){
echo "Found " . $needle . " at the end of " . $haystack . "!";
}
在这种情况下,不需要函数startsWith()作为
(strpos($stringToSearch, $doesItStartWithThis) === 0)
将准确返回true或false。
奇怪的是,这么简单,所有的野生函数都在这里泛滥。
Fastest endsWith()解决方案:
# Checks if a string ends in a string
function endsWith($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
到目前为止,所有的答案似乎都做了大量不必要的工作、strlen计算、字符串分配(substr)等。“strpos”和“stripos”函数返回$haystack中$needle第一次出现的索引:
function startsWith($haystack,$needle,$case=true)
{
if ($case)
return strpos($haystack, $needle, 0) === 0;
return stripos($haystack, $needle, 0) === 0;
}
function endsWith($haystack,$needle,$case=true)
{
$expectedPosition = strlen($haystack) - strlen($needle);
if ($case)
return strrpos($haystack, $needle, 0) === $expectedPosition;
return strripos($haystack, $needle, 0) === $expectedPosition;
}
拉里维尔9.0
如果你正在使用Laravel,那么你可以执行以下操作(如果你没有使用Laraver,那么你真的应该这样做)。
Str::of('a long string')->startsWith('a');
Str::of('a long string')->endsWith('string');
//true
//true
做得更快:
function startsWith($haystack,$needle) {
if($needle==="") return true;
if($haystack[0]<>$needle[0]) return false; // ------------------------- speed boost!
return (0===substr_compare($haystack,$needle,0,strlen($needle)));
}
这一行比较字符串的第一个字符,可以使false case会立即返回,因此会进行许多比较速度快得多(测量时快7倍)。在真实的情况下,你几乎没有为这条线付出任何性能代价,所以我认为这是值得的。(此外,在实践中,当您为一个特定的起始块测试多个字符串时,大多数比较都会失败,因为在典型的情况下,您正在寻找一些东西。)
注意:@Tino下面评论中的bug已经修复
对于字符串与整数
如果要强制字符串比较(即,期望startsWith(“1234”,12)为true),则需要一些类型转换:
function startsWith($haystack,$needle) {
if($needle==="") return true;
$haystack = (string)$haystack;
$needle = (string)$needle;
if($haystack[0]<>$needle[0]) return false; // ------------------------- speed boost!
return (0===substr_compare($haystack,$needle,0,strlen($needle)));
}
我不认为这是必要的,但这是一个有趣的边缘案例,导致了诸如“布尔值真以t开头吗?”这样的问题,所以你要做出决定,但要确保你的决定是好的。