User Contributed Notes
Functies |
 add a note |
brooke at wayport dot net
08-Nov-1999 07:21 |
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Many people ask how to call functions that are in other files. See
"Require" and "Include" in the manual. Also the value
of $DOCUMENT_ROOT is good for including sub-includes. (It is NOT like
C/C++ includes. The dir is ALWAYS relative to the main source file.)
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php at paintbot dot com
05-Feb-2000 02:32 |
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Important Note to All New Users: functions do NOT have default access to
GLOBAL variables. You must specify globals as such in your function using
the 'global' type/keyword. See the section on
variables:scope.
This note should also be added to the
documentation, as it would help the majority of programmers who use
languages where globals are, well, global (that is, available from
anywhere). The scoping rules should also not be buried in subsection 4 of
the variables section. It should be front and center because I think this
is probably one of the most non-standard and thus confusing design choices
of PHP.
[Ed. note: the variables $_GET, $_POST, $_REQUEST,
$_SESSION, and $_FILES are superglobals, which means you don't need the
global keyword to use them inside a function]
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cap at capsi dot cx
22-Feb-2000 11:19 |
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When using a function within a function, using global in the inner function
will not make variables available that have been first initialized within
the outer function.
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GMCardoe at netherworldrpg dot net
24-Apr-2000 09:02 |
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Stack overflow means your function called itself recursivly too many times
and just completely filled up the processes stack. That error is there to
stop a recursive call from completely taking up the entire system memory.
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php-general at list dot php dot net
05-Dec-2000 11:51 |
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If a user-defined function does not explicitly return a value, then it
will return NULL. For most truth tests, this can be considered as
FALSE.
For example:
function print_list
($array)
{
print implode ("<br />",
$array);
}
if (print_list ($HTTP_POST_VARS))
print
"The print_list function returned a value that can be considered
true."
else
print "The print_list function returned a
value that can be considered false."
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kop at meme dot com
14-Dec-2000 10:14 |
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See also about controlling the generation of error messages by putting @ in
front of the function before you call it, in the section "error
control operators".
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21-Dec-2000 05:41 |
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Function names are case-insensitive in PHP 3 and PHP 4.
For
example, if you have function foo, you can call it using foo(), FoO(),
FOO(), etc..
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yasuo_ohgaki at hotmail dot com
09-Mar-2001 05:42 |
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PHP supports recursion. I thought it worth to mention.
Simple
Quick Sort using recursion works perfectly.
== OUTPUT
==
Recursion TEST
Array
(
[0] => 12
[1] => 23
[2] => 35
[3] => 45
[4] =>
56
[5] => 67
)
== END OUTPUT ==
== QUICK SORT
CODE ==
<?php
echo('
Recursion
TEST
');
function swap(&$v, $i, $j) {
$temp =
$v[$i];
$v[$i] = $v[$j];
$v[$j] = $temp;
}
// Quick
Sort integer array - $int_array[$left] .. $int_array[$right]
function
qsort(&$int_array, $left, $right) {
if ($left >= $right)
return; // Do nothing if there are less than 2 array elements
swap
($int_array, $left, intval(($left+$right)/2));
$last = $left;
for ($i = $left + 1; $i <= $right; $i++)
if ($int_array[$i] <
$int_array[$left])
swap($int_array, ++$last, $i);
swap($int_array, $left, $last);
qsort($int_array, $left,
$last-1);
qsort($int_array, $last+1, $right);
}
$val =
array(56,23,45,67,12,35);
qsort($val, 0,
count($val)-1);
echo '<pre>';
print_r ($val);
echo
'</pre>';
?>
== END QUICK SORT ==
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aboyd at ssti dot com
05-Apr-2001 03:34 |
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[Editor's note: put your includes in the beginning of your script. You can
call an included function, after it has been included
--jeroen]
The documentation states: "In PHP 3, functions
must be defined before they are referenced. No such requirement exists in
PHP 4."
I thought it wise to note here that there is in fact
a limitation: you cannot bury your function in an include() or require().
If the function is in an include()'d file, there is NO way to call that
function beforehand. The workaround is to put the function directly in
the file that calls the function.
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xpaz at somm dot com
14-Nov-2001 07:47 |
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It is possible to define a function from inside another function.
The
result is that the inner function does not exist until the outer function
gets executed.
For example, the following
code:
function a () {
function b() {
echo "I
am b.\n";
}
echo "I am a.\n";
}
if
(function_exists("b")) echo "b is defined.\n"; else
echo "b is not defined.\n";
a();
if
(function_exists("b")) echo "b is defined.\n"; else
echo "b is not defined.\n";
echoes:
b is not
defined.
I am a.
b is defined.
Classes too can be defined
inside functions, and will not exist until the outer function gets
executed.
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fabio at city dot ac dot uk
14-Feb-2002 01:57 |
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As a corollary to other people's contributions in this section, you have to
be careful when transforming a piece of code in to a function (say F1). If
this piece of code contains calls to another function (say F2), then each
variable used in F2 and defined in F1 must be declared as GLOBAL both in
F1 and F2. This is tricky.
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bishop
01-May-2002 02:49 |
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The documentation statement:
"In PHP 3, functions must be
defined before they are referenced. No such requirement exists in PHP
4."
is not entirely accurate (or at least
misleading).
Consider:
function a() {
function b() {
echo 'I am b';
}
echo 'I am a';
}
You MUST
call a() before you can even think about using b(). Why? The parser
hasn't touched the scope inside function a (for efficiency reasons), so b
has yet to be defined or even *declared*.
The documentation (I
believe) refers to this behaviour:
a();
function a() {
echo
'I am a';
}
which is perfectly valid and runs as you probably
expect. However, the following does not work as expected (or
documented):
function a() {
b();
function b()
{
echo 'I am b';
}
echo 'I am
a';
}
a();
Rather than getting "I am b"
followed by "I am a" you get a parse error ("Call to
undefined function b()").
So, the bottom line:
Gewaehrleistungsausschluss
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bishop
01-May-2002 02:54 |
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Consider:
function a() {
function b() {
echo 'I am
b';
}
echo 'I am a';
}
a();
a();
As you
might NOT expect, the second call to a() fails with a "Cannot
redeclare b()" error. This behaviour is correct, insofar as PHP
doesn't "allow functions to be redefined."
A work
around:
function a() {
if ( ! function_exists('b') ) {
function b() {
echo 'I am b';
}
}
echo 'I am a';
}
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devciti at yahoo dot com
20-Jun-2002 04:51 |
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I have some problems with functions. I want to create some kind of 'tell me
the configuration function'. Like this:
<?php
function
TellConfig(){
$header_file_to_use =
"header.inc";
$footer_file_to_user =
"footer.inc";
}
//Wont
Work!
TellConfig();
include($header_file_to_use);
echo
"Body!";
include($footer_file_to_use);
/*
Is there a
way to call a variable set by a function? As i dont know this is the way i
am doing it
*/
$header_file_to_use =
"";
$footer_file_to_use = "";
function
TellConfig2(){
global $header_file_to_use,
$footer_file_to_use;
$header_file_to_use =
"header.inc";
$footer_file_to_use =
"footer.inc";
}
TellConfig2();
include($header_file_to_use);
echo
"body 2!";
include($footer_file_to_use);
// This
works
?>
Even i dont want to use a function for configuration
vars this is a good example.
:P
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germanAlonso at keltoi-web dot com
10-Aug-2002 02:17 |
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Although [email protected] has already pointed the recursion support
on PHP, here's another example, wich shows clearly the mechanism of
recursive algorithms:
function fact($i){
if($i==1){
return 1;
}else{
return $i*fact($i-1);
}
}
It
returns $i! (supposing $i is a valid positive integer greater than 0).
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matt at smidwap dot com
14-Aug-2002 12:26 |
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[Editor's note: that is the reason why 'function' and others are
"reserved words", see:
for more details]
Creating a function with the name 'function'
won't turn up errors, but when calling that function, nothing will be
returned. Example:
<?php
function();
function
function () {
print "Hello, world!";
}
//
"Hello, world!" will not be printed.
?>
I assume
this is because when calling 'function', php thinks you are trying to
create a new function.
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06-Sep-2002 08:41 |
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If you need to use "real" global variables, accessible from any
function, without the need to declare them explicity, take a look at (join
these 2 lines please):
s=1ac53d13a815427f145d5dedf6a10023&threadid=10209242
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albaity at php4web dot com
26-Oct-2002 02:06 |
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To use class from function
you need first to load class OUT the
function
and then you can use the class functions from your function
example :
class Cart
{
var $items; // Items in our
shopping cart
// Add $num articles of $artnr to the cart
function add_item ($artnr, $num)
{
$this->items[$artnr] += $num;
}
// Take $num
articles of $artnr out of the cart
function remove_item
($artnr, $num)
{
if ($this->items[$artnr] > $num)
{
$this->items[$artnr] -= $num;
return
true;
} else {
return false;
}
}
}
------------------------
<?php
$cart = new
Cart;
function additem($var1,$var2){
$cart->add_item($var1,
$var2);
}
additem(1,10);
?>
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allen at brooker dot gb dot net
21-Nov-2002 03:23 |
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Does anyone have a list of all the characters allowed in function
names?
So far I've only used a-z 0-9 _ and -
I assume (), {},
[], ', ", $, % and & are not allowed.
What other
characters are legal and what aren't?
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bitparanoid at yahoo dot com
15-Dec-2002 05:38 |
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Example 13.1 has an extra curly brace which will throw back an
error:
function bar() {
{
echo "I exist
immediately....
}
should be:
function bar() {
echo
"I exist immediately...
}
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misc dot anders at feder dot dk
24-Dec-2002 10:28 |
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PHP allows you to address functions in a very dynamic way:
$foo =
"bar";
$foo("fubar");
The above will call
the bar function with the "fubar" argument.
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mittag /// add /// marcmittag /// de
23-Jan-2003 11:31 |
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To devciti at yahoo dot com
The section "returning values"
of the docu says:
=====
You can't return multiple values from a
function, but similar results can be obtained by returning a list.
function small_numbers()
{
return array (0, 1,
2);
}
list ($zero, $one, $two) = small_numbers();
=====
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nutbar at innocent dot com
12-Mar-2003 07:06 |
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Regarding the comments about having to declare global variables inside of
functions before you can use them...
Lots of you seem to complain
about having to declare lots of variables, when really there's one simple
solution to this:
global $GLOBALS;
This will define the
$GLOBALS variable inside your code, and since that variable is basically
like the mother of all variables - *presto*, you now have access to any
variable in PHP.
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gayard at ig dot com dot br
04-Apr-2003 10:58 |
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In PHP 4.3.0, I have found a bug in declaring functions within
functions:
<?
function MyZero($x) {
function
GreaterThanZero() { echo "Greater"; }
function
LessThanZero() { echo "LessThan"; }
function
EqualToZero() { echo "Equal"; }
if ($x > 0)
GreaterThanZero();
else if ($x < 0) LessThanZero();
else
EqualToZero();
}
MyZero(1);
MyZero(0);
MyZero(-1);
?>
The output is:
Greater
Fatal error:
Cannot redeclare greaterthanzero() (previously declared in
/home/php/public_html/teste.php:4) in /home/php/public_html/teste.php on
line 4
My advice is: declare functions like you did in C, that is
one function at a time. This seems to work fine.
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php at simoneast dot net
11-Apr-2003 04:59 |
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If you're frustrated by not having access to global variables from within
your functions, instead of declaring each one (particularly if you don't
know them all) there are a couple of workarounds...
If your
function just needs to read global variables...
function
aCoolFunction () {
extract($GLOBALS);
....
This creates a
copy of all the global variables in the function scope. Notice that
because it's a copy of the variables, changing them won't affect the
variables outside the function and the copies are lost at the conclusion
of the function.
If you need to write to your global variables, I
haven't tested it, but you could probably loop through the $GLOBALS array
and make a "global" declaration for each one. Then you could
modify the variables.
Please note that this shouldn't be standard
practice, but only in the case where a function needs access to all the
global variables when they may be different from one call to another. Use
the "global var1, var2..." declaration where
possible.
Hope that helps some people.
Simon.
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Storm
10-May-2003 02:55 |
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I think it worthy of noting (for noobies such as myself):
You can define
access to a global variable before it is defined when defining a function
as long as the variable is defined before the function is called. This had
me baffled for a few hours til I tried it out...lol. Here's a quick
example:
Perfectly valid:
-------------------------
function
hello() {
global $hi;
echo $hi;
}
$hi = 'Hi
There!'; // Var defined after function is
defined
hello();
-------------------------
I know most of
the Gurus persay already knew this, but I didn't! :p This helps ;-)
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Syntax
Basis syntax
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