何时使用strtr vs str_replace? [英] When to use strtr vs str_replace?

问题描述

我很难理解何时strtr比str_replace更可取，反之亦然.尽管替换子字符串的顺序相反，但是使用这两个函数似乎都可能获得完全相同的结果.例如:

I'm having a hard time understanding when strtr would be preferable to str_replace or vice versa. It seems that it's possible to achieve the exact same results using either function, although the order in which substrings are replaced is reversed. For example:

echo strtr('test string', 'st', 'XY')."\n";
echo strtr('test string', array( 's' => 'X', 't' => 'Y', 'st' => 'Z' ))."\n";
echo str_replace(array('s', 't', 'st'), array('X', 'Y', 'Z'), 'test string')."\n";
echo str_replace(array('st', 't', 's'), array('Z', 'Y', 'X'), 'test string');

此输出

YeXY XYring
YeZ Zring
YeXY XYring
YeZ Zring

除语法外，使用一种语法比使用另一种语法有什么好处吗?在任何情况下都不足以达到预期的结果吗?

Aside from syntax, is there any benefit to using one over the other? Any cases where one would not be sufficient to achieve a desired result?

推荐答案

第一个区别:

PHP手册的注释部分提供了一个有趣的例子，说明strtr和str_replace之间的不同行为:

An interesting example of a different behaviour between strtr and str_replace is in the comments section of the PHP Manual:

<?php
$arrFrom = array("1","2","3","B");
$arrTo = array("A","B","C","D");
$word = "ZBB2";
echo str_replace($arrFrom, $arrTo, $word);
?>

• 我希望结果是:"ZDDB"
• 但是，此返回:"ZDDD" (因为根据我们的数组，B = D)
• I would expect as result: "ZDDB"
• However, this return: "ZDDD" (Because B = D according to our array)

要执行此操作，请改用"strtr":

To make this work, use "strtr" instead:

<?php
$arr = array("1" => "A","2" => "B","3" => "C","B" => "D");
$word = "ZBB2";
echo strtr($word,$arr);
?>

• 这将返回:"ZDDB"

这意味着str_replace是一种更全局的替换方法，而strtr只是简单地逐个转换字符.

This means that str_replace is a more global approach to replacements, while strtr simply translates the chars one by one.

另一个区别:

给出以下代码(摘自 PHP字符串替换速度比较 ):

Given the following code (taken from PHP String Replacement Speed Comparison):

<?php
$text = "PHP: Hypertext Preprocessor";

$text_strtr = strtr($text
    , array("PHP" => "PHP: Hypertext Preprocessor"
        , "PHP: Hypertext Preprocessor" => "PHP"));
$text_str_replace = str_replace(array("PHP", "PHP: Hypertext Preprocessor")
    , array("PHP: Hypertext Preprocessor", "PHP")
    , $text);
var_dump($text_strtr);
var_dump($text_str_replace);
?>

结果文本行将是:

string(3)"PHP"
string(27)"PHP:超文本预处理器"

string(3) "PHP"
string(27) "PHP: Hypertext Preprocessor"

---

主要解释:

发生这种情况是因为:

• strtr :它按长度降序对参数进行排序，因此:

• strtr: it sorts its parameters by length, in descending order, so:

1. 它将使最大的字符更重要"，然后，由于主题文本本身是替换数组的最大键，因此将其翻译.
2. 因为主题文本的所有字符已被替换，所以该过程到此结束.

• str_replace :按定义键的顺序工作，因此:

• str_replace: it works in the order the keys are defined, so:

  它在主题文本中找到键"PHP"，并将其替换为:"PHP:超文本预处理器"，其结果如下:
  1. it finds the key "PHP" in the subject text and replaces it with: "PHP: Hypertext Preprocessor", what gives as result:

  "PHP:超文本预处理器:超文本预处理器".

  "PHP: Hypertext Preprocessor: Hypertext Preprocessor".

• 然后在上一步的结果文本中找到下一个键:"PHP:超文本预处理器"，因此将其替换为"PHP"，其结果为:

• then it finds the next key: "PHP: Hypertext Preprocessor" in the resulting text of the former step, so it gets replaced by "PHP", which gives as result:

  "PHP:超文本预处理器".

  "PHP: Hypertext Preprocessor".

• 没有更多要查找的键，因此替换在此处结束.

• there are no more keys to look for, so the replacement ends there.

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