什么时候使用 strtr vs str_place？

我很难理解什么时候 strtr会比 str_replace更好，反之亦然。虽然子字符串的替换顺序是相反的，但似乎可以使用任何一个函数得到完全相同的结果。例如:

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');

这个输出

YeXY XYring
YeZ Zring
YeXY XYring
YeZ Zring

除了语法之外，使用一种语法对另一种语法有什么好处吗？在任何情况下，一个人不足以达到预期的结果？

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It seems that it's possible to achieve the exact same results using either function

That's not always true and depends on the search and replace data you provide. For example where the two function differ see: Does PHP str_replace have a greater than 13 character limit?

  • strtr will not replace in parts of the string that already have been replaced - str_replace will replace inside replaces.
  • strtr will start with the longest key first in case you call it with two parameters - str_replace will replace from left to right.
  • str_replace can return the number of replacements done - strtr does not offer such a count value.
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最佳答案

First difference:

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);
?>
  • I would expect as result: "ZDDB"
  • However, this return: "ZDDD" (Because B = D according to our array)

To make this work, use "strtr" instead:

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

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

Another difference:

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);
?>

The resulting lines of text will be:

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

The main explanation:

This happens because:

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

    1. it will give "more importance" to the largest one, and then, as the subject text is itself the largest key of the replacement array, it gets translated.
    2. because all the chars of the subject text have been replaced, the process ends there.

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

    1. it finds the key “PHP” in the subject text and replaces it with: “PHP: Hypertext Preprocessor”, what gives as result:

      “PHP: Hypertext Preprocessor: Hypertext Preprocessor”.

    2. 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: Hypertext Preprocessor”.

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

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I think strtr provides more flexible and conditional replacement when used with two arguments, for example: if string is 1, replace with a, but if string is 10, replace with b. This trick could only be achieved by strtr.

$string = "1.10.0001";
echo strtr($string, array("1" => "a", "10" => "b"));
// a.b.000a

see : Php Manual Strtr.

小开

Notice in manual STRTR-- Description string strtr ( string $str , string $from , string $to ) string strtr ( string $str , array $replace_pairs ) If given three arguments, this function returns a copy of str where ...

STR_REPLACE-- ... If search or replace are arrays, their elements are processed first to last. ...

STRTR each turn NOT effect to next, BUT STR_REPLACE does.


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