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Оператор управления ошибками Побитовые операторы

Last updated: Sat, 27 Jan 2007

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# Операторы сравнения

Операторы сравнения, как это видно из их названия, позволяют сравнивать между собой два значения. Также вам возможно будет интересно ознакомиться с разделом Сравнение типов, в котором приведено большое количество соответствующих примеров.

Таблица 15-4. Операторы сравнения

Пример | Название | Результат
--- | --- | ---
$a == $b | Равно | `TRUE` если $a равно $b.
$a === $b | Тождественно равно | `TRUE` если $a равно $b и имеет тот же тип. (Добавлено в PHP 4)
$a != $b | Не равно | `TRUE` если $a не равно $b.
$a <> $b | Не равно | `TRUE` если $a не равно $b.
$a !== $b | Тождественно не равно | `TRUE` если $a не равно $b или в случае, если они разных типов (Добавлено в PHP 4)
$a < $b | Меньше | `TRUE` если $a строго меньше $b.
$a > $b | Больше | `TRUE` если $a строго больше $b.
$a <= $b | Меньше или равно | `TRUE` если $a is меньше или равно $b.
$a >= $b | Больше или равно | `TRUE` если $a больше или равно $b.

В случае, если вы сравниваете целое со строкой, строка будет преобразована к числу. В случае, если вы сравниваете две числовые строки, они сравниваются как целые числа. Эти правила также распространяются на оператор switch.

`<?php
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
switch ("a") {
case 0:
echo "0";
break;
case "a": // Эта ветка никогда не будет достигнута, так как "a" уже сопоставленно с 0
echo "a";
break;
}
?>`

Еще одним условным оператором является тернарный оператор "?:".

`<?php
// Пример использования тернарного оператора
$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];
// Приведенный выше код аналогичен следующему блоку с использованием if/else
if (empty($_POST['action'])) {
$action = 'default';
} else {
$action = $_POST['action'];
}
?>`

Выражение `(expr1) ? (expr2) : (expr3)` интерпретируется как `expr2`, если `expr1` вычисляется в `TRUE`, или как `expr3` если `expr1` вычисляется в `FALSE`.

Также ознакомьтесь с описаниями функций strcasecmp(), strcmp(), и разделом документации Типы и Операторы, работающие с массивами.

add a note User Contributed Notes
Операторы сравнения
floppie at quadra-tec dot net
06-Mar-2007 10:34
`I also ran a benchmark of equals versus identical on my own server. I found the difference to be surprisingly significant (average of 15% across multiple executions of the script). Just for kicks I had it compare int to float speed as well and that came up to roughly 40% faster in favor of int (in equal/identical comparisons - no idea how they perform otherwise), and had it compare ==/=== to !=/!== and came up to negligible difference (averages out to 0). Here are the results over 100k iterations - if you want to know exactly what comparisons were done let me know:
100000 iterations
total identical 36.142370939255
total equals 41.991316795349
total is 38.998074293137
total not 39.135613441467
total int 29.253834247589
total float 48.879853487015
%gain identical vs equals 13.928941272788
%gain is vs not 0.35144242350103
%gain int vs float 40.151550872875
total time 78.15989112854`
thomas dot oldbury at tgohome dot com
27-Feb-2007 09:37
`Be careful when using the ternary operator!
The following will not evaluate to the expected result:
<?php
echo "a string that has a " . (true) ? 'true' : 'false' . " condition in. ";
?>
Will print true.
Instead, use this:
<?php
echo "a string that has a " . ((true) ? 'true' : 'false') . " condition in. ";
?>
This will evaluate to the expected result: "a string that has a true condition in. "
I hope this helps.`
fernandoleal at dragoncs dot com
03-Feb-2007 11:19
`If you need nested ifs on I var its important to group the if so it works.
Example:
<?php
//Dont Works
//Parse error: parse error, unexpected ':'
$var='<option value="1" '.$status == "1" ? 'selected="selected"' :''.'>Value 1</option>';
//Works:
$var='<option value="1" '.($status == "1" ? 'selected="selected"' :'').'>Value 1</option>';
echo $var;
?>`
stepheneliotdewey at gmail [period] com
07-Jan-2007 06:49
`Note that typecasting will NOT prevent the default behavior for converting two numeric strings to numbers when comparing them.
e.g.:
if ((string) '0123' == (string) '123')
print 'equals';
else
print 'doesn\'t equal';
Still prints 'equals'
As far as I can tell the only way to avoid this is to use the identity comparison operators (=== and !==).`
Stephen
07-Jan-2007 05:12
`Regarding gamephreak AT removethis gmail DOT com,
I found those results interesting, so I decided to test them on my own dedicated server. I found that actually, the identity and equality operators are almost exactly the same speed when dealing with numbers and/or strings (I did not test arrays, objects, etc). I ran the same tests plus a couple of inequality tests as well, this time over a 100,000 iteration loop (rounded to 7 significant digits using round()). :
'foo' == 'foo': 0.0130451
'foo' === 'foo': 0.0124481
42 == 42: 0.0124421
42 === 42: 0.0124369
'foo' == 'bar': 0.0124562
'foo' === 'bar': 0.012475
42 == 43: 0.012471
42 === 43: 0.0124719
'42' == 42: 0.0124779
'42' === 42: 0.0124731
'42' == 43: 0.0124722
'42' === 43: 0.01248
42 != 43: 0.012444
42 !== 43: 0.0124211
This was just one snapshot, though. If I refreshed the page I was using to test this, sometimes the "winners" would reverse. In other words, no operator was clearly faster, and I think that system "noise" is may usually be more significant than the speed of these operators.
Here is sample code for one of the loops:
$time1 = microtime(true);
for ($i = 0; $i < 100000; $i++){
'42' == 43;
}
$time2 = microtime(true);
print "'42' == 43: " . round($time2 - $time1, 7) . '<br><br>';
The lesson here is that you should make your coding decisions based on what makes more sense from a logical perspective, and not what is faster. Personally I hate the equality operator since PHP's dynamic typing makes it unpredictable (e.g. two strings compared may both be cast as numbers...).`
04-Jan-2007 07:11
`Since php 5.2 the operator == for object vs object is not recursion safe, it will cause a fatal error if one of the objects contains a refernce to it self (indirect refferences also counts here).
If you are just checking if two object pointers points to the same object use === instead and aviod this issue (you might get a minimal speed bost too).`
bishop
26-Oct-2006 03:49
`When you want to know if two arrays contain the same values, regardless of the values' order, you cannot use "==" or "===". In other words:
<?php
(array(1,2) == array(2,1)) === false;
?>
To answer that question, use:
<?php
function array_equal($a, $b) {
return (is_array($a) && is_array($b) && array_diff($a, $b) === array_diff($b, $a));
}
?>
A related, but more strict problem, is if you need to ensure that two arrays contain the same key=>value pairs, regardless of the order of the pairs. In that case, use:
<?php
function array_identical($a, $b) {
return (is_array($a) && is_array($b) && array_diff_assoc($a, $b) === array_diff_assoc($b, $a));
}
?>
Example:
<?php
$a = array (2, 1);
$b = array (1, 2);
// true === array_equal($a, $b);
// false === array_identical($a, $b);
$a = array ('a' => 2, 'b' => 1);
$b = array ('b' => 1, 'a' => 2);
// true === array_identical($a, $b)
// true === array_equal($a, $b)
?>
(See also the solution "rshawiii at yahoo dot com" posted)`
pcdinh at phpvietnam dot net
10-Aug-2006 09:50
`You should be very careful when using == with an result set returned from a query that can be an empty array, multi-dimensional array or a boolean false value (if the query failed to execute). In PHP, an empty array is equivalent to true.
[php]
$myArray = array();
// check if there is any error with the query
if ($myArray == false)
{
echo "Yes";
}
[/php]
return Yes
Use === instead.`
gamephreak AT removethis gmail DOT com
17-Jul-2006 04:28
`"Identical to" is faster compared to "equals to." I ran a test script that compared various combinations of strings and integers over a 10000x loop. Sample results:
'foo' v. 'foo' eq: 0.00274
'foo' v. 'foo' id: 0.001671
42 v. 42 eq: 0.00171
42 v. 42 id: 0.001436
'foo' v. 'bar' eq: 0.002589
'foo' v. 'bar' id: 0.001658
42 v. 43 eq: 0.001719
42 v. 43 id: 0.001419
'42' v. 42 eq: 0.00223
'42' v. 42 id: 0.001392
'42' v. 43 eq: 0.002281
'42' v. 43 id: 0.001389`
Alex
17-May-2006 07:49
`I think everybody should read carefully what "jeronimo at DELETE_THIS dot transartmedia dot com" wrote. It's a great pitfall even for seasoned programmers and should be looked upon with a great attention.
For example, comparing passwords with == may result in a very large security hole.
I would add some more to it:
The workaround is to use strcmp() or ===.
Note on ===:
While the php documentation says that, basically,
($a===$b) is the same as ($a==$b && gettype($a) == gettype($b)),
this is not true.
The difference between == and === is that === never does any type conversion. So, while, according to documentation, ("+0.1" === ".1") should return true (because both are strings and == returns true), === actually returns false (which is good).`
adam at caucho dot com
08-May-2006 10:49
`Note: according to the spec, PHP's comparison
operators are not transitive. For example,
the following are all true in PHP5:
"11" < "a" < 2 < "11"
As a result, the outcome of sorting an array
depends on the order the elements appear
in the pre-sort array. The following code will
dump out two arrays with *different* orderings:
<?php
$a = array(2, "a", "11", 2);
$b = array(2, "11", "a", 2);
sort($a);
var_dump($a);
sort($b);
var_dump($b);
?>
This is not a bug report -- given the spec on
this documentation page, what PHP does is
"correct". But that may not be what was
intended...`
kroczu at interia dot pl
14-Feb-2006 05:26
`<?
//attention about this case!
$a=0;
if($a=="some string..."){ /* (...) -> true! */ }
if($a==="some string..."){ /* (...) -> false */ }
$a=1;
if($a=="some string..."){ /*(...) -> false */ }
if($a==="some string..."){ /*(...) -> false */ }
?>`
rshawiii at yahoo dot com
18-Jan-2006 11:36
`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 === $a2
}`
johnjc-phpdocs at publicinfo dot net
01-Nov-2005 10:41
`The === and !== are not fully documented in either the Comparison Operator, Booleans type sections. They are talked about a bit more in the sections on strpos() and array_search() but those sections refer you to the section on Booleans for further information.
I am putting my contribution on === and !== in the Booleans section with pointers to it from the comment areas of other sections.
http://uk.php.net/manual/en/language.types.boolean.php`
sam at liddicott dot com
01-Nov-2005 07:42
`Don't be deceived into thinking that === compares objects for identity, it does not. It does a recusrive comparison which fails if there are recusrive object references involved, and will report as identical two different object instances that happen to merely have the same value.
You can see the stated problem at: http://bugs.php.net/bug.php?id=35053
My workaround is php::CompareObjects($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 $result;
}
}`
07-Sep-2005 01:09
`The following contrasts the trinary operator associativity in PHP and Java. The first test would work as expected in Java (evaluates left-to-right, associates right-to-left, like if stmnt), the second in PHP (evaluates and associates left-to-right)
<?php
echo "\n\n######----------- trinary operator associativity\n\n";
function trinaryTest($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 03:40
`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 06:34
`Float values comparation:
if ( (string) $a == (string) $b) {
print 'a is equal to b';
} else {
print 'a is not equal to b';
}`
sven dot heyll at web dot de
05-Dec-2004 01:19
`Hi folks,
to the float comparison problem...
This worked for me:
//! compare two floating point values, return true if they are equal
//! (enough) or false otherwise
function float_equal($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 03:47
`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 03:35
`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 $var = 0.3 caused me are unbelievable. even though the stored variable WAS 0.3 it was still ignoring it - this was to do with the internal float not recognising it as 0.3 even though it *displayed* it as 0.3 when echo'd or printed... basically it was stored imprecisly, but not able to display it as such.
I ended up having to compare after multiplying by 10, rounding, and then dividing by 10... rediculous, but sadly the only way I could find to reliably do it. The round seemed to remove the break in the float...
jesus that took me ages to find...`
hiroh2k at yahoo dot com
19-Oct-2004 11:05
`if you want to use the ?: operator, you should be careful with the precedence.
Here's an example of the priority of operators:
echo 'Hello, ' . isset($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, ' . $guestusername . ', please register');
for general rule, if you mix ?: with other sentences, always close it with parentheses.`
jeronimo at DELETE_THIS dot transartmedia dot com
02-Jul-2004 04:01
`For converted Perl programmers: use strict comparison operators (===, !==) in place of string comparison operators (eq, ne). Don't use the simple equality operators (==, !=), because ($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");
// Prints: EQUAL
// Surrounding the strings with single quotes (') instead of double
// quotes (") to ensure the contents aren't evaluated, and forcing
// string types has no effect.
echo ( (string)'0001' == (string)'+1.' ? "EQUAL" : "not equal");
// Prints: EQUAL
// Including non-digit characters (like leading spaces, "e", the plus
// or minus sign, period, ...) can still result in this behavior, if
// a string happens to be valid scientific notation.
echo (' 131e-2' == '001.3100' ? "EQUAL" : "not equal");
// Prints: 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...
<?
// Same examples as above, using === instead of ==
echo ("007" === "7" ? "EQUAL" : "not equal");
// Prints: not equal
echo ( (string)'0001' === (string)'+1.' ? "EQUAL" : "not equal");
// Prints: not equal
echo (' 131e-2' === '001.3100' ? "EQUAL" : "not equal");
// Prints: not equal
?>`
webmaster __AT__ digitalanime __DOT__ nl
13-Apr-2004 03:31
`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 03:17
`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
03-Jan-2004 04:15
`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( $right ) ) )
{
return TRUE;
}
else
{
return FALSE;
}
}
}
?>
1 === '1' is the same as is_identical( 1, '1' ).`
jwhiting at hampshire dot edu
09-Dec-2003 03:31
`note: the behavior below is documented in the appendix K about type comparisons, but since it is somewhat buried i thought i should raise it here for people since it threw me for a loop until i figured it out completely.
just to clarify a tricky point about the == comparison operator when dealing with strings and numbers:
('some string' == 0) returns TRUE
however, ('123' == 0) returns FALSE
also note that ((int) 'some string') returns 0
and ((int) '123') returns 123
the behavior makes senes but you must be careful when comparing strings to numbers, e.g. when you're comparing a request variable which you expect to be numeric. its easy to fall into the trap of:
if ($_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
03-Dec-2003 03:03
`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
12-Nov-2003 06:27
`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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Оператор управления ошибками Побитовые операторы

Last updated: Sat, 27 Jan 2007
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Last updated: Sat Mar 10 09:32:46 2007 PST