运算符
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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。

运算符
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PHP手册 - N: 字符串运算符

用户评论:

krzysiek (05-Apr-2012 05:19)

echo 1 ..2; will output 10.2

this is because "1" is contatenated with "0.2"

hexidecimalgadget at hotmail dot com (10-Feb-2009 05:37)

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

?>

mariusads::at::helpedia.com (27-Aug-2008 10:44)

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.

mehea (20-May-2008 01:31)

I thought string operators were for use with strings or strings and numbers.  But that is incorrect.  You can use the '.' operator to concatenate two numbers, as follows:

echo 1 . 2;

I assume that behind the scenes the 1 and 2 are converted to strings to allow the concatenation.  What triggers the conversion? I'll guess the dot operator.

kevin at metalaxe dot com (10-Nov-2006 02:57)

I ran the follow script and found that using "$var" was 'mostly' slower than using ' '.$var

<?php
$var = 1;

for( $x=0; $x < 101; $x++ )
{
    echo '<br /><br />var = int( '.$var.' )<br />';
   
    $timer->reset();
    for( $i=0; $i<100001; $i++ )
    {
        $string = " {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var} {$var}";
        unset( $string );
    }
    echo 'One string with 15 $vars was set using one concat 100000 times and took '.$timer->fetch_time().' seconds to execute <br />';
   
    $timer->reset();
    for( $i=0; $i<100001; $i++ )
    {
        $string = ' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var.' '.$var;
        unset( $string );
    }
    echo 'One string with 15 instances of $var was set using multiple concats 100000 times and took '.$timer->fetch_time().' seconds to execute';
}
exit();
?>

Replacing $timer with a generic timing class of course.

caliban at darklock dot com (29-Mar-2006 07:10)

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 03:10)

<?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 03:57)

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 (27-Apr-2004 05:53)

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);
?>