php - substr 与字符串中的破折号一起工作很奇怪

Question

我有以下三种情况，我希望显示相同的输出，但它对 $str1 做了一些奇怪的事情:

<?php
$str1 = "— lorem lorem Alice lorem lorem lorem loremlorem";
//       | < Why would a dash make a difference in the the found index?
$str2 = "a lorem lorem Alice lorem lorem lorem loremlorem";
$str3 = "  lorem lorem Alice lorem lorem lorem loremlorem";


// The found index is always the same
$foundIndex = mb_stripos($str1, "Alice"); 
var_dump(substr($str1, $foundIndex - 6, 24), $foundIndex);

$foundIndex = mb_stripos($str2, "Alice");
var_dump(substr($str2, $foundIndex - 6, 24), $foundIndex);

$foundIndex = mb_stripos($str3, "Alice");
var_dump(substr($str3, $foundIndex - 6, 24), $foundIndex);

输出:

string(24) "m lorem Alice lorem lore"     << Why is this swapped to the right one char?
int(14)
string(24) "lorem Alice lorem lorem "
int(14)
string(24) "lorem Alice lorem lorem "
int(14)

你可以测试一下here .

我使用操作 mb_stripos 和 substr 来搜索字符串，这就是 PoC。

这是为什么？如何修复包含特殊字符的字符串的行为？

---

经过快速检查，我认为 — 占用了三个字节，而 substr 按字节工作，而不是按字符工作。 strlen("—") 也是 3...

如何按字符而不是按字节对字符串进行切片？按字节切片对我来说实际上不起作用。并且所有特殊字符都应该正确处理。如果我没记错的话，表情符号也有不同的尺寸!

Answer 1

您使用的破折号是多字节字符。要执行多字节安全 substr() 操作，您需要使用 mb_substr()。

<?php
$str1 = "— lorem lorem Alice lorem lorem lorem loremlorem";
//       | < Why would a dash make a difference in the the found index?
$str2 = "a lorem lorem Alice lorem lorem lorem loremlorem";
$str3 = "  lorem lorem Alice lorem lorem lorem loremlorem";


// The found index is always the same
$foundIndex = mb_stripos($str1, "Alice"); 
var_dump(mb_substr($str1, $foundIndex - 6, 24), $foundIndex);

$foundIndex = mb_stripos($str2, "Alice");
var_dump(mb_substr($str2, $foundIndex - 6, 24), $foundIndex);

$foundIndex = mb_stripos($str3, "Alice");
var_dump(mb_substr($str3, $foundIndex - 6, 24), $foundIndex);