PHP: 文字列演算子

文字列演算子

文字列の演算子は 2 種類あります。最初のは結合演算子('.')で、右引数と左引数を結合したものを返します。2 番目は、結合代入演算子('.=')で、この演算子は右側の引数に左側の引数を追加します。詳細は、代入演算子を参照ください。

<?php
$a = "Hello ";
$b = $a . "World!"; // $b は、"Hello World!" となります。

$a = "Hello ";
$a .= "World!"; // $a は、"Hello World!" となります。
?>

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User Contributed Notes 6 notes

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262

K.Alex ¶

11 years ago

As for me, curly braces serve good substitution for concatenation, and they are quicker to type and code looks cleaner. Remember to use double quotes (" ") as their content is parced by php, because in single quotes (' ') you'll get litaral name of variable provided:

<?php

 $a = '12345';

// This works:
 echo "qwe{$a}rty"; // qwe12345rty, using braces
 echo "qwe" . $a . "rty"; // qwe12345rty, concatenation used

// Does not work:
 echo 'qwe{$a}rty'; // qwe{$a}rty, single quotes are not parsed
 echo "qwe$arty"; // qwe, because $a became $arty, which is undefined

?>

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168

anders dot benke at telia dot com ¶

20 years ago

A word of caution - the dot operator has the same precedence as + and -, which can yield unexpected results. 

Example:

<php
$var = 3;

echo "Result: " . $var + 3;
?>

The above will print out "3" instead of "Result: 6", since first the string "Result3" is created and this is then added to 3 yielding 3, non-empty non-numeric strings being converted to 0.

To print "Result: 6", use parantheses to alter precedence:

<php
$var = 3;

echo "Result: " . ($var + 3); 
?>

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109

Stephen Clay ¶

18 years ago

<?php 
"{$str1}{$str2}{$str3}"; // one concat = fast
  $str1. $str2. $str3;   // two concats = slow
?>
Use double quotes to concat more than two strings instead of multiple '.' operators.  PHP is forced to re-concatenate with every '.' operator.

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hexidecimalgadget at hotmail dot com ¶

15 years ago

If you attempt to add numbers with a concatenation operator, your result will be the result of those numbers as strings.

<?php

echo "thr"."ee";           //prints the string "three"
echo "twe" . "lve";        //prints the string "twelve"
echo 1 . 2;                //prints the string "12"
echo 1.2;                  //prints the number 1.2
echo 1+2;                  //prints the number 3

?>

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biziclop ¶

2 years ago

Some bitwise operators (the and, or, xor and not operators: & | ^ ~ ) also work with strings too since PHP4, so you don't have to loop through strings and do chr(ord($s[i])) like things.

See the documentation of the bitwise operators: https://www.php.net/operators.bitwise

<?php var_dump(
  ('23456787654' ^ 'zVXYYhoXDYP'), // 'Hello_World'
  ('(!($)^!)@$@' | '@ddhfIvn2H$'), // 'hello_world'
  ('{}~|o!Wo{|}' & 'Lgmno|Wovmf'), // 'Hello World'
  (~'<0-14)(98'  &   '}}}}}}}}}')  // 'AMPLITUDE'
); ?>

Live demo: https://3v4l.org/MnFeb

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mariusads::at::helpedia.com ¶

16 years ago

Be careful so that you don't type "." instead of ";" at the end of a line.

It took me more than 30 minutes to debug a long script because of something like this:

<?
echo 'a'.
$c = 'x';
echo 'b';
echo 'c';
?>

The output is "axbc", because of the dot on the first line.

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