在 preg_replace() 之前使用 strpos() 更快吗？

Question

假设我们在数百万 post 个字符串上使用这个 preg_replace：

function makeClickableLinks($s) {
    return preg_replace('@(https?://([-\w\.]+[-\w])+(:\d+)?(/([\w/_\.#-]*(\?\S+)?[^\.\s])?)?)@', '<a href="" target="_blank"></a>', $s);
}

假设所有 post 中只有 10% 包含链接，在调用 preg_replace() 之前检查 strpos($string, 'http') !== false 会更快吗？如果是这样，为什么？ preg_replace() 不在内部进行一些预测试吗？

Answer 1

是的，使用像 strpos() 这样的简单搜索比编译和执行正则表达式要快得多，这是在替换本身必须发生的内存复制之上。如果您正在做数百或数千，那么没有意义，但如果您正在做数百万（尤其是如果其中只有 10% 包含 http），那么首先进行简单搜索将变得值得。

最终，要 100% 确定的唯一方法是对其进行基准测试，但我相当确定您将首先使用 strpos() 获得一些改进。

Answer 2

令人惊讶的是，是的！

以下是您使用这两个函数分析 10,000,000 个字符串的基准：

测试 1 - 匹配模式的字符串：

"Here is a great new site to visit at http://example.com so go there now!"

preg_replace alone took 10.9626309872 seconds
strpos before preg_replace took 12.6124269962 seconds ← slower

测试 2 - 与模式不匹配的字符串：

"Here is a great new site to visit at ftp://example.com so go there now!"

preg_replace alone took 6.51636195183 seconds
strpos before preg_replace took 2.91205692291 seconds ← faster

测试 3 - 10% 的字符串匹配模式：

"Here is a great new site to visit at ftp://example.com so go there now!" (90%)
"Here is a great new site to visit at http://example.com so go there now!" (10%)

preg_replace alone took 7.43295097351 seconds
strpos before preg_replace took 4.31978201866 seconds ← faster

这只是两个字符串的简单基准测试，但速度有明显差异。

这是“10%”案例的测试工具：

<?php
$string1 = "Here is a great new site to visit at http://example.com so go there now!";
$string2 = "Here is a great new site to visit at ftp://example.com so go there now!";

function makeClickableLinks1($s) {
    return preg_replace('@(https?://([-\w\.]+[-\w])+(:\d+)?(/([\w/_\.#-]*(\?\S+)?[^\.\s])?)?)@', '<a href="" target="_blank"></a>', $s);
}

function makeClickableLinks2($s) {
    return strpos($s, 'http') !== false ? preg_replace('@(https?://([-\w\.]+[-\w])+(:\d+)?(/([\w/_\.#-]*(\?\S+)?[^\.\s])?)?)@', '<a href="" target="_blank"></a>', $s) : null;
}

/* Begin test harness */

$loops = 10000000;

function microtime_float() {
    list($usec, $sec) = explode(" ", microtime());
    return ((float)$usec + (float)$sec);
}

/* Test using only preg_replace */

$time_start = microtime_float();
for($i = 0; $i < $loops; $i++) {
    // Only 10% of strings will have "http"
    makeClickableLinks1($i % 10 ? $string2 : $string1);
}
$time_end = microtime_float();
$time = $time_end - $time_start;
echo "preg_replace alone took $time seconds<br/>";

/* Test using strpos before preg_replace */

$time_start = microtime_float();
for($i = 0; $i < $loops; $i++) {
    // Only 10% of strings will have "http"
    makeClickableLinks2($i % 10 ? $string2 : $string1);
}
$time_end = microtime_float();
$time = $time_end - $time_start;
echo "strpos before preg_replace took $time seconds<br/>";
?>

在 preg_replace() 之前使用 strpos() 更快吗？

Is using strpos() before preg_replace() faster?

php

regex

preg-replace

strpos