字符串运算符

有两个字符串运算符。第一个是连接运算符（“.”），它返回其左右参数连接后的字符串。第二个是连接赋值运算符（“.=”），它将右边参数附加到左边的参数后。更多信息见赋值运算符。


<?php
$a = "Hello ";
$b = $a . "World!"; // now $b contains "Hello World!"

$a = "Hello ";
$a .= "World!";     // now $a contains "Hello World!"
?>

参见字符串类型和字符串函数章节。

add a note User Contributed Notes

caliban at darklock dot com
30-Mar-2006 03:10


WRT Stephen's note:



My example of concatenation and array methods of string building does not include the interstitial logic, which is expected to include conditionals. 



Concatenation method:



$str="This is my list";

if($list=="o") $str.="<ol>";

else $str.="<ul>";

foreach($item as $i) $str.="<li>$i</li>";

if($list=="o") $str.="</ol>";

else $str.="</ul>";



Array method: 



$str=array("This is my list");

if($list=="o") $str[]="<ol>";

else $str[]="<ul>";

foreach($item as $i) $str[]="<li>$i</li>";

if($list=="o") $str[]="</ol>";

else $str[]="</ul>";

$str=implode("",$str);



You can't do either of these with a single double-quoted string. However, if what you are doing CAN be done in a single double-quoted string, Stephen is completely correct in observing that you should do that instead of concatenating.

Stephen Clay
23-Dec-2005 11:10


<?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.

caliban at darklock dot com
15-Dec-2004 11:57


String concatenation is faster than the array method:



$str="";

$str.="Some string";

$str.="Some other string";

...

$str.="The last string";



That runs roughly twice as fast as:



$str=array();

$str[]="Some string";

$str[]="Some other string";

...

$str[]="The last string";

$str=implode("",$str);



Not that I think this is a terribly widespread practice, but I've got an awful lot of legacy code with this array method in it and a comment to the effect that it's faster than string concatenation. Testing has shown the exact opposite, so I figured I'd enlighten anyone else with this misconception.

anders dot benke at telia dot com
28-Apr-2004 12:53


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); 

?>

php dot net at rinner dot at
20-Feb-2001 09:00


Also see http://www.php.net/manual/en/language.types.string.php for usage of  here doc syntax ("<<<")

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