PHP: Operadores de Cadena

Last updated: Fri, 22 Aug 2008

Operadores de Cadena

Existen dos operadores para datos tipo string. El primero es el operador de concatenación ('.'), el cual devuelve el resultado de concatenar sus argumentas a lado derecho e izquierdo. El segundo es el operador de asignación sobre concatenación ('.='), el cual adiciona el argumento del lado derecho al argumento en el lado izquierdo. Por favor consulte Operadores de Asignación para más información.


<?php
$a = "¡Hola ";
$b = $a . "Mundo!"; // ahora $b contiene "¡Hola Mundo!"

$a = "¡Hola ";
$a .= "Mundo!";     // ahora $a contiene "¡Hola Mundo!"
?>

Vea también las secciones del manual sobre el tipo String y las funciones de Cadenas.

Operadores de Matrices

Operadores de Lógica

Last updated: Fri, 22 Aug 2008

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Operadores de Cadena

mariusads::at::helpedia.com
27-Aug-2008 11:44


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 02:31


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 03:57


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 09:10


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 04:10


<?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 04:57


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 06:53


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); 

?>

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Operadores de Matrices

Operadores de Lógica

Last updated: Fri, 22 Aug 2008