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Fejezet 8. V�ltoz�kAlapok
PHP-ban a v�ltoz�kat egy doll�rjel ut�ni v�ltoz�n�v jel�li.
A v�ltoz�nevek �rz�kenyek kis- �s nagybet�k k�l�nb�z�s�g�re.
A v�ltoz�nevekre a PHP m�s jelz�ivel azonos szab�lyok vonatkoznak.
Egy �rv�nyes v�ltoz�n�v bet�vel vagy al�h�z�ssal kezd�dik,
amit tetsz�leges sz�m� bet�, sz�m vagy al�h�z�s k�vet.
Regul�ris kifejez�ssel kifejezve ez a k�vetkez�t jelenti:
'[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*'
Megjegyz�s:
Ebben az esetben egy bet� lehet az angol abc egy bet�je
a-z-ig �s A-Z-ig, valamint a 127-t�l 255-ig terjed�
(0x7f-0xff) ASCII k�d� karakterek.
PHP 3-ban a v�ltoz�khoz mindig �rt�kek tartoznak. Vagyis ha
egy kifejez�st rendel�nk egy v�ltoz�hoz, az eredeti kifejez�s
eg�sz�nek �rt�ke m�sol�dik a c�lv�ltoz�ba. Ez azt jelenti, hogy
ha p�ld�ul egy v�ltoz� �rt�k�t egy m�sikhoz rendelj�k, egyik�k
megv�ltoz�sa sincs hat�ssal a m�sikra. N�zd �t
Kifejez�sek c. fejezetet,
ahol az ilyen jelleg� hozz�rendel�sekr�l t�bb inform�ci� tal�lhat�.
PHP 4-ben lehet�s�g van egy m�sik hozz�rendel�si m�dra:
v�ltoz� referencia szerinti hozz�rendel�s�re.
Ez azt jelenti, hogy az �j v�ltoz� egyszer�en hivatkozik (m�s sz�val
"alias lesz", vagy "r� mutat") az eredetire.
Az �j v�ltoz�n v�gzett v�ltoztat�sok az eredetit is �rintik
�s ford�tva. Ez azt is jelenti, hogy nem t�rt�nik m�sol�s;
ekk�ppen a hozz�rendel�s gyorsabban t�rt�nik meg. Igaz ugyan,
hogy ez a sebess�gn�veked�s csak "feszes" ciklusokban vagy
nagy t�mb�kn�l ill. objektumok �tad�sakor jelentkezik.
Referencia szerinti �rt�kad�shoz egyszer�en & jelet kell
az �tadand� v�ltoz� neve el� �rni. Az al�bbi k�d - p�ld�ul - ki�rja
k�tszer, hogy 'Nevem Bob':
Fontos megjegyezni, hogy csak megnevezett v�ltoz�kra
lehet referenci�t l�trehozni.
User Contributed Notes
V�ltoz�k |
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[email protected]
23-Mar-2001 10:31 |
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If, for some reason you need to declare
a dynamic variable global, say
$usertype1, $usertype2 etc...
do it like this:
$i=1;
$ready=#number of
generated
variables#
while ($i <
$ready) {
$var="usertype$i";
global
$$var;
###do the action with
the var, for
example:##
echo $$var;
$i++;
}
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[email protected]
24-Apr-2001 05:31 |
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I had trouble digging this out, and searches for various terms (memory
model, garbage collection, &c) were not productive.
PHP4
uses reference counting for garbage collection. Details about this system
can be found here:
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[email protected]
08-Dec-2001 01:12 |
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a great way to pass variables from page to page...
select:
How PHP/FI handles GET and POST method data
ie:
/cgi-bin/php.cgi/[email protected]&var=value
The
relevant components of the PHP symbol table will be:
$argc
= 4
$argv[0] = abc
$argv[1] = def
$argv[2] = [email protected]&var=value
$EMAIL_ADDR = [email protected]
$var = value
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[email protected]
13-Jan-2002 10:21 |
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Here is a tip to save the bandwidth rainforest. There is no reason to
send meta tags to Mozilla compatible
browsers.
<?php
if(!strstr($HTTP_USER_AGENT,
"Mozilla")) {
?>
<meta name="author"
content="I, me and myself" />
<? } ?>
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[email protected]
01-Mar-2002 02:06 |
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Actually, you can use other chars (including spaces) in the variable name,
if you are using variable variables. E.g., the following works for me (in
PHP 4.1.1):
$x="blah
blah-blah";
$$x="value";
echo "var==" .
$$x;
echo "var==" . ${"blah blah-blah"};
Its
output is:
var==value
var==value
You can use it also in
object variables (properties).
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[email protected]
18-Mar-2002 01:37 |
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'Here document' syntax is explained under the 'echo' function. Somehow I
always try to find it here... In short:
echo
<<<EOD
blablabla
tralala
EOD;
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[email protected]
19-Mar-2002 09:31 |
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In the example listed above:
<?php
$foo = 'Bob';
// Assign the value 'Bob' to $foo
$bar = &$foo; //
Reference $foo via $bar.
$bar = "My name is $bar"; // Alter
$bar...
echo $foo; // $foo is altered too.
echo
$bar;
?>
the documentation above it is somewhat
ambiguous:
$bar = &$foo means that $foo becomes the reference for
$bar, thus $foo = "Bob". As I read it, $bar should've become
the reference for $foo, took me a bit to turn it around. Just some
clarification.
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[email protected]
06-Apr-2002 08:16 |
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Another way to assign a variable a large amount text without having to
worry about quotes getting in the way is like so:
$aVariable =
<<<END
"HEY!"
END;
print
"$aVariable";
output: "HEY!"
Where as
this is will produce an error:
$aVariable =
""HEY!"";
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[email protected]
14-Apr-2002 02:21 |
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<<------------------< Env. Variables
>------------------>
If you are looking for an explanation of
environment variables, go to
If
you wanted to set environment variables, look into the putenv()
function.
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[email protected]
25-May-2002 04:53 |
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How does one send a variable from a particular page, over a secure network
that uses SSL in order for it to be processed by the web server?
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[email protected]
03-Jul-2002 03:05 |
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Can someone tell me why this page (www.gbasquare.host.sk/news/news.php)
doesn't work??? Yesterday it worked but today the server has upgraded the
php script and the page doesn't work. Thank you
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stlawson AT sbcglobal DOT net
06-Jul-2002 12:47 |
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In 'ghent's comment on the 'above example' I think he confuses the
confusion ;)
Here is the example referred
to:
<?php
$foo = 'Bob'; // Assign the value
'Bob' to $foo
$bar = &$foo; // Reference $foo via
$bar.
$bar = "My name is $bar"; // Alter $bar...
echo
$bar;
echo $foo; // $foo is altered
too.
?>
�Reference $foo via $bar�/�Alter $bar�� IS correct,
but it is a little obscure. Here�s what it means:
$bar is assigned
a reference to $foo, thus $bar �references� or points to $foo which
contains the string �Bob�. Essentially what is happening here is �Bob� is
stored in memory at a particular address. &$foo returns that address
[where �Bob� is stored]. That address is assigned to $bar. So, in the
string �My name is $bar�, $bar �uses� the address it contains to find
�Bob� (which is �in� $foo) and thus the string becomes �My name is Bob�.
When the string is assigned to $bar, because $bar refers to $foo, it gets
assigned to the same address location that �Bob� is stored at, thus �Bob�
is overwritten by �My name is Bob�. The trick here is to realize that
$bar behaves as if it is $foo, so when something is assigned to $bar (the
alias of $foo), it�s as if it was being assigned to $foo!
After the
above script is run, the output will look like this:
My name is
BobMy name is Bob
e.g. both $foo and $bar print the same
thing.
In �C++� the same code snippit would look like
this:
foo = �Bob� ;
bar = &foo ;
bar = �My name is � +
*bar ;
Notice that in C/C++ it is necessary to manually dereference
the pointer (*bar) � PHP does this automagically.
BTW: You might
think that �echo $bar;� would display the address of $foo � not so! More
PHP automagic ;)
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[email protected]
13-Jul-2002 02:24 |
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Can I call array items multiply as Perl?
It
seems:
$x=array(1,2,3,4,5,6,7,8);
$y=$x[3,1,5,7,-1];
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[email protected]
18-Aug-2002 03:01 |
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If you use global variables within a function, take note that changing the
variable keyword from "global", somewhere down the line, to
"return", that that variable can either be one or the other. It
can't be both "returned" and "global".
So, if
within a function you have on line x:
global $var;
and then on
line x+1:
return $var;
that $var becomes no longer global, and
instead just and only "returned".
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