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Z mojej strony serwisowi należy się bardzo mocna pochwała. Nawet późna pora zgłoszenia problemu (23.00) nie przeszkodziła Darkowi w jego rozwiązaniu. Do tego poziom odpisywania na maile jest bardzo wysoki... wszystko wykłada jak cierpliwy nauczyciel. Śmiało mogę przyznać, że zamieszczone na stronach porady są rzeczowo opisane - a nie jak to bywa w innych serwisach mamy sam kod i nic poza tym! Jeszcze raz wielkie dzięki!
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Jak wskazuje ich nazwa, operatory te służą do porównywania dwóch wartości.
Tabela 15-4. Operaatory Porównania | Przykład | Nazwa | Opis |
|---|
| $a == $b | Równy | TRUE jesli $a jest równe $b | | $a === $b | Identyczny |
TRUE jeśli $a jest równe $b, i obydwa operandy są tego samego typu.
(tylko w PHP 4)
| | $a != $b | Różny | TRUE jeśli $a nie jest równy $b. | | $a <> $b | Różny | TRUE jeśli $a nie jest równy $b. | | $a !== $b | Nie identyczny |
TRUE jeśli $a nie jest równy $b, lub nie są tego samego typu.
(tylko w PHP 4)
| | $a < $b | Mniejszy niż | TRUE jeśli $a jest mniejszy od $b. | | $a > $b | Większy niż | TRUE jeśli $a jest większy od $b. | | $a <= $b | Mniejszy lub równy | TRUE jeśli $a jest mniejszy lub równy $b. | | $a >= $b | Większy lub równy | TRUE jeśli $a jest większy lub równy $b. |
Jeszcze jednym operatorem warunkowym jest operator "?:" (tzw. ternariusz
- operator trójargumentowy),
działający tak jak w C i wielu innych językach.
Wartością wyrażenia jest expr2, jeśli
expr1 jest równe TRUE, lub
expr3, jeśli
expr1 jest równe FALSE.
User Contributed Notesrshawiii at yahoo dot com
18-Jan-2006 08:36
You can't just compare two arrays with the === operator
like you would think to find out if they are equal or not. This is more complicated when you have multi-dimensional arrays. Here is a recursive comparison function.
/**
* Compares two arrays to see if they contain the same values. Returns TRUE or FALSE.
* usefull for determining if a record or block of data was modified (perhaps by user input)
* prior to setting a "date_last_updated" or skipping updating the db in the case of no change.
*
* @param array $a1
* @param array $a2
* @return boolean
*/
function array_compare_recursive($a1, $a2)
{
if (!(is_array($a1) and (is_array($a2)))) { return FALSE;}
if (!count($a1) == count($a2))
{
return FALSE; // arrays don't have same number of entries
}
foreach ($a1 as $key => $val)
{
if (!array_key_exists($key, $a2))
{return FALSE; // uncomparable array keys don't match
}
elseif (is_array($val) and is_array($a2[$key])) // if both entries are arrays then compare recursive
{if (!array_compare_recursive($val,$a2[$key])) return FALSE;
}
elseif (!($val === $a2[$key])) // compare entries must be of same type.
{return FALSE;
}
}
return TRUE; // $a1 === $a2
}
johnjc-phpdocs at publicinfo dot net
01-Nov-2005 07:41
The === and !== are not fully documented in either the Comparison Operator, Booleans type sections. They are talked about a bit more in the sections on strpos() and array_search() but those sections refer you to the section on Booleans for further information.
I am putting my contribution on === and !== in the Booleans section with pointers to it from the comment areas of other sections.
http://uk.php.net/manual/en/language.types.boolean.php
sam at liddicott dot com
01-Nov-2005 04:42
Don't be deceived into thinking that === compares objects for identity, it does not. It does a recusrive comparison which fails if there are recusrive object references involved, and will report as identical two different object instances that happen to merely have the same value.
You can see the stated problem at: http://bugs.php.net/bug.php?id=35053
My workaround is php::CompareObjects($a,$b)
# static class to hold methods to encapsulate php deficiencies in various versions
class php {
# in === on objects in php4 does a dumb recusrive check instead
function CompareObject(&$a,&$b) {
$value='Bah! Stupid===';
$key="bah".rand(0,1000);
while(isset($a->$key)) $key.=rand(0,9);
if (isset($b->$key)) return FALSE;
$a->$key=$value;
$result=($a->$key===$b->$key);
unset($a->$key);
return $result;
}
}
07-Sep-2005 10:09
The following contrasts the trinary operator associativity in PHP and Java. The first test would work as expected in Java (evaluates left-to-right, associates right-to-left, like if stmnt), the second in PHP (evaluates and associates left-to-right)
<?php
echo "\n\n######----------- trinary operator associativity\n\n";
function trinaryTest($foo){
$bar = $foo > 20
? "greater than 20"
: $foo > 10
? "greater than 10"
: $foo > 5
? "greater than 5"
: "not worthy of consideration";
echo $foo." => ".$bar."\n";
}
echo "----trinaryTest\n\n";
trinaryTest(21);
trinaryTest(11);
trinaryTest(6);
trinaryTest(4);
function trinaryTestParens($foo){
$bar = $foo > 20
? "greater than 20"
: ($foo > 10
? "greater than 10"
: ($foo > 5
? "greater than 5"
: "not worthy of consideration"));
echo $foo." => ".$bar."\n";
}
echo "----trinaryTestParens\n\n";
trinaryTestParens(21);
trinaryTestParens(11);
trinaryTest(6);
trinaryTestParens(4);
?>
Output:
######----------- trinary operator associativity
----trinaryTest
21 => greater than 5
11 => greater than 5
6 => greater than 5
4 => not worthy of consideration
----trinaryTestParens
21 => greater than 20
11 => greater than 10
6 => greater than 5
4 => not worthy of consideration
pandreas81 at NO dot gmx dot SPAM dot de
02-Jun-2005 12:40
Please note that the example in some notes before is not 100% correct, because it misses the call of abs().
To compare a float you should use abs($myFloat - 0.3) < EPSILON. This way of comparison is very common in other languages and it's cleaner than converting the values to strings. I suggest using a constant instead of a variable for EPSILON.
mita at abv dot bg
24-Mar-2005 03:34
Float values comparation:
if ( (string) $a == (string) $b) {
print 'a is equal to b';
} else {
print 'a is not equal to b';
}
sven dot heyll at web dot de
05-Dec-2004 10:19
Hi folks,
to the float comparison problem...
This worked for me:
//! compare two floating point values, return true if they are equal
//! (enough) or false otherwise
function float_equal($f1, $f2)
{
return ($f1 > $f2) ? (false) : (!($f1 < $f2));
}
// compare floats
$f1 = 0.037;
$f2 = 1000387.978;
echo "$f1 and $f2 are ".(float_equal($f1,$f2)?("equal"):("not equal"))."<br />";
$f1 = 0.3;
$f2 = 0.3;
echo "$f1 and $f2 are ".(float_equal($f1,$f2)?("equal"):("not equal"))."<br />";
02-Dec-2004 12:47
Concerning floats: It is simply pointless to compare a float with the value "0.3". The number 0.3 is not exactly representable in binary. Period. So is the number 0.1, and an infinite number of others numbers. Just like 1/3 is not exactly representable in decimal. How would you code the test for your float to be one third? Maybe $myFloat == 0.33333333333 Hmm: you see: Everyone would agree that this test is not accurate.
The test $myFloat == 0.3 is making exactly the same mistake.
So the float which you think should be 0.3 is really something very close to it; if you print it in decimal, the conversion will end up with the closest decimal representation, which may well be "0.3". But "0.3" is also the "right display decimal" for hundreds of float values.
The correct way to "compare" floats is: ( $myFloat - 0.3 ) < $EPSILON where $EPSILON is something like 1e-10, depending on your application. Approximate algorithms are the only right way to treat floats, which are only approximate by themselves.
darkcryst at gmail dot com
21-Oct-2004 12:35
be REALLY careful when comparing float values. PHP, like most languages, is vunerable to he problems of floating point precision.
Do NOT compare floats directly, and this also means any decimal value at all.
The headaches finding out if $var = 0.3 caused me are unbelievable. even though the stored variable WAS 0.3 it was still ignoring it - this was to do with the internal float not recognising it as 0.3 even though it *displayed* it as 0.3 when echo'd or printed... basically it was stored imprecisly, but not able to display it as such.
I ended up having to compare after multiplying by 10, rounding, and then dividing by 10... rediculous, but sadly the only way I could find to reliably do it. The round seemed to remove the break in the float...
jesus that took me ages to find...
hiroh2k at yahoo dot com
19-Oct-2004 08:05
if you want to use the ?: operator, you should be careful with the precedence.
Here's an example of the priority of operators:
echo 'Hello, ' . isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register';
This make "'Hello, ' . isset($i)" the sentence to evaluate. So, if you think to mix more sentences with the ?: operator, please use always parentheses to force the proper evaluation of the sentence.
echo 'Hello, ' . (isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register');
for general rule, if you mix ?: with other sentences, always close it with parentheses.
jeronimo at DELETE_THIS dot transartmedia dot com
02-Jul-2004 01:01
For converted Perl programmers: use strict comparison operators (===, !==) in place of string comparison operators (eq, ne). Don't use the simple equality operators (==, !=), because ($a == $b) will return TRUE in many situations where ($a eq $b) would return FALSE.
For instance...
"mary" == "fred" is FALSE, but
"+010" == "10.0" is TRUE (!)
In the following examples, none of the strings being compared are identical, but because PHP *can* evaluate them as numbers, it does so, and therefore finds them equal...
<?
echo ("007" == "7" ? "EQUAL" : "not equal");
echo ( (string)'0001' == (string)'+1.' ? "EQUAL" : "not equal");
echo (' 131e-2' == '001.3100' ? "EQUAL" : "not equal");
?>
If you're comparing passwords (or anything else for which "near" precision isn't good enough) this confusion could be detrimental. Stick with strict comparisons...
<?
echo ("007" === "7" ? "EQUAL" : "not equal");
echo ( (string)'0001' === (string)'+1.' ? "EQUAL" : "not equal");
echo (' 131e-2' === '001.3100' ? "EQUAL" : "not equal");
?>
webmaster __AT__ digitalanime __DOT__ nl
14-Apr-2004 12:31
WARNING!!!!
Let's say, we have this little script:
<?php
$username = 'Me';
$guestusername = 'Guest';
echo 'Hello, ' . isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register';
?>
What you want:
If $i is set, display:
Hello, my friend: Me, how are you doing?
If not, display:
Hello, my guest, Guest, please register
BUT, you DON'T get that result!
If $i is set, you get this:
my friend: Me, how are you doing? (so, there's not "Hello, " before it)
If $i is NOT set, you get this:
my friend: Me, how are you doing?
So... That's the same!
You can solve this by using the "(" and ")" to give priority to the ternary operator:
<?php
$username = 'Me';
$guestusername = 'Guest';
echo 'Hello, ' . (isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register');
?>
When $i is set, you get this:
Hello, my friend: Me, how are you doing? (expected)
When $i is NOT set, you get this:
Hello, my guest, Guest, please register (expected too)
So.. Please, don't be dumb and ALWAYS use the priority-signs (or.. How do you call them?), ( and ).
By using them, you won't get unneeded trouble and always know for sure your code is doing what you want: The right thing.
user@example
04-Apr-2004 12:17
With Nested ternary Operators you have to set the logical parentheses to get the correct result.
<?php
$test=true;
$test2=true;
($test) ? "TEST1 true" : ($test2) ? "TEST2 true" : "false";
?>
This will output: TEST2 true;
correct:
<?php
$test=true;
$test2=true;
($test) ? "TEST1 true" : (($test2) ? "TEST2 true" : "false");
?>
Anyway don't nest them to much....!!
gphemsley at users dot sourceforge dot net
04-Jan-2004 01:15
For those of you who need to use === with PHP 3, this should do the trick:
<?php
function is_identical( $left, $right )
{
if( phpversion() >= 4 )
{
return ( $left === $right );
}
else
{
if( ( $left == $right ) && ( gettype( $left ) == gettype( $right ) ) )
{
return TRUE;
}
else
{
return FALSE;
}
}
}
?>
1 === '1' is the same as is_identical( 1, '1' ).
jwhiting at hampshire dot edu
10-Dec-2003 12:31
note: the behavior below is documented in the appendix K about type comparisons, but since it is somewhat buried i thought i should raise it here for people since it threw me for a loop until i figured it out completely.
just to clarify a tricky point about the == comparison operator when dealing with strings and numbers:
('some string' == 0) returns TRUE
however, ('123' == 0) returns FALSE
also note that ((int) 'some string') returns 0
and ((int) '123') returns 123
the behavior makes senes but you must be careful when comparing strings to numbers, e.g. when you're comparing a request variable which you expect to be numeric. its easy to fall into the trap of:
if ($_GET['myvar']==0) dosomething();
as this will dosomething() even when $_GET['myvar'] is 'some string' and clearly not the value 0
i was getting lazy with my types since php vars are so flexible, so be warned to pay attention to the details...
mina86 at tlen dot pl
04-Dec-2003 12:03
I guess quicker method would be:
<?php
$colors = array('#EEEEEE', '#FFFFFF');
while ($i++ < 10) {
?>
<tr bgColor="<?=$colors[$i%2]?>">
<td>Cell 1-<?=$i?></td>
<td>Cell 2-<?=$i?></td>
<td>Cell 3-<?=$i?></td>
<td>Cell 4-<?=$i?></td>
</tr>
<?php } ?>
And you can easily add more colors:
<?php
$colors = array('#EEEEEE', '#FFFFFF', '#DDDDDD', '#CCCCCC');
while ($i++ < 10) {
?>
<tr bgColor="<?=$colors[$i%4]?>">
<td>Cell 1-<?=$i?></td>
<td>Cell 2-<?=$i?></td>
<td>Cell 3-<?=$i?></td>
<td>Cell 4-<?=$i?></td>
</tr>
<?php } ?>
xhenxhe
13-Nov-2003 03:27
This operator is very is usefull and will save you time and lines once you get the hang of it. Try this next time you are looping through rows in a table and want to change the bgColor:
<table border=1 width=100% align=center style="border-collapse: collapse" bgColor="lightblue">
<tr>
<td>Column 1</td>
<td>Column 2</td>
<td>Column 3</td>
<td>Column 4</td>
</tr>
<?
while ($i++ < 10)
{
$rbg = $rbg=="#EEEEEE" ? "#FFFFFF" : "#EEEEEE";
?>
<tr bgColor="<?=$rbg?>">
<td>Cell 1-<?=$i?></td>
<td>Cell 2-<?=$i?></td>
<td>Cell 3-<?=$i?></td>
<td>Cell 4-<?=$i?></td>
</tr>
<? } ?>
</table>
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