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

您可以为此使用fnmatch函数。

// Starts with.
fnmatch('prefix*', $haystack);
// Ends with.
fnmatch('*suffix', $haystack);

其他回答

PHP 8.0及更高版本

从PHP 8.0开始,您可以使用

str_starts_with手册和

str_ends_with手动

实例

echo str_starts_with($str,'|');

8.0之前的PHP

function startsWith( $haystack, $needle ) {
     $length = strlen( $needle );
     return substr( $haystack, 0, $length ) === $needle;
}
function endsWith( $haystack, $needle ) {
    $length = strlen( $needle );
    if( !$length ) {
        return true;
    }
    return substr( $haystack, -$length ) === $needle;
}

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。

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;
}

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

您可以为此使用fnmatch函数。

// Starts with.
fnmatch('prefix*', $haystack);
// Ends with.
fnmatch('*suffix', $haystack);