소개
inline if syntax:
echo (True==True) ? 'true' : 'false';
is the same as:
if(True==True) echo 'true';
else echo 'false';
if
if문은 PHP를 포함해서 모든 언어에 있어서 가장 중요한 기능 중 하나이다. 이 제어문으로 각각 다른 코드에 대해 조건적인 수행을 가능케한다. if문의 기능은 C와 비슷하다:
if (expr)
statement
표현식에 관한 섹션에서 설명된것처럼 expr은 논리(Boolean)값으로 취급된다. expr이 TRUE와 같다면 PHP는 statement를 수행할것이고, FALSE라면 무시될것이다. 무슨값이 FALSE인지 알려면 '논리값으로 변환하기' 섹션을 참고한다.
다음 예는 $a가 $b보다 크다면 a는 b보다 크다를 출력할 것이다.
<?php
if ($a > $b)
echo "a는 b보다 크다";
?>
종종 하나 이상의 구문을 조건적으로 수행시켜야 하는 때가 있다. 물론 if절로 각 구문을 감싸줄 필요는 없다. 대신, 구문 그룹안에 몇개의 구문을 그룹화할 수 있다. 예를 들면, 이코드는 $a가 $b보다 크다면 a는 b보다 크다라고 출력할것이고, $a의 값을 $b로 지정하게 될것이다.
<?php
if ($a > $b) {
echo "a는 b보다 크다";
$b = $a;
}
?>
If문은 다른 if문안에 무한정으로 내포될수 있다. 이와 같은 기능은 프로그램의 여러부분을 조건적으로 수행하기 위한 유연성을 제공한다.
add a note
User Contributed Notes
if
gung foo priest
22-Jan-2012 08:13
bimal at sanjaal dot com
07-Jul-2011 02:21
PHP compares numbers inside quotations, in an interesting way.
This can create confusions to those who did not refer this manual, but expected something different.
<?php
define('NUMBER', 13);
$number = NUMBER;
if('13_2' == NUMBER) { echo('Why matched?'); };
if('13_2' == "{$number}") { echo('Why not matched?'); }
?>
In the above example, the first comparison matches; that you don't expect.
The second comparison does not match.
lallemand dot mathieu at gmail dot com
31-Mar-2011 06:01
Be careful when you chain inline "if" :
<?php
$x = 1;
$y = 3;
echo ($x==1) ? "One" : ($y == 2) ? "Two" : "None";
?>
Expected result : "One".
Result on screen : "Two".
Pretty disapointing isn't it ?
So, if you want to chain inline "if" you have to use parentesis on each test like below:
<?php
$x=1;
$y=3;
echo ($x==1) ? "One" : ( ($y==2) ? "Two" : "None" );
?>
Result on screen : "One".
Hope it helps !
Donny Nyamweya
11-Feb-2011 08:30
In addition to the traditional syntax for if (condition) action;
I am fond of the ternary operator that does the same thing, but with fewer words and code to type:
(condition ? action_if_true: action_if_false;)
example
(x > y? 'Passed the test' : 'Failed the test')
Christian L.
25-Jan-2011 10:58
An other way for controls is the ternary operator (see Comparison Operators) that can be used as follows:
<?php
$v = 1;
$r = (1 == $v) ? 'Yes' : 'No'; // $r is set to 'Yes'
$r = (3 == $v) ? 'Yes' : 'No'; // $r is set to 'No'
echo (1 == $v) ? 'Yes' : 'No'; // 'Yes' will be printed
// and since PHP 5.3
$v = 'My Value';
$r = ($v) ?: 'No Value'; // $r is set to 'My Value' because $v is evaluated to TRUE
$v = '';
echo ($v) ?: 'No Value'; // 'No Value' will be printed because $v is evaluated to FALSE
?>
Parentheses can be left out in all examples above.
techguy14 at gmail dot com
06-Jan-2011 01:39
You can have 'nested' if statements withing a single if statement, using additional parenthesis.
For example, instead of having:
<?php
if( $a == 1 || $a == 2 ) {
if( $b == 3 || $b == 4 ) {
if( $c == 5 || $ d == 6 ) {
//Do something here.
}
}
}
?>
You could just simply do this:
<?php
if( ($a==1 || $a==2) && ($b==3 || $b==4) && ($c==5 || $c==6) ) {
//do that something here.
}
?>
Hope this helps!
admin at leonard !spam challis dot com
22-Nov-2010 04:41
When using if statements without the curly braces, remember than only one statement will be executed as part of that condition. If you want to place multiple statements you must use curly braces, and not just put them on the same line.
<?php
if (1==0) echo "Test 1."; echo "Test 2";
?>
Whereas some people would expect nothing to be displayed, this piece of code will show: "Test 2".
Rudi
14-Sep-2010 01:14
Note that safe type checking (using === and !== instead of == and !=) is in general somewhat faster. When you're using non-safe type checking and a conversion is really needed for checking, safe type checking is considerably faster.
===================================
Test (100,000,000 runs):
<?php
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if(5 == 10) {}
$end = microtime(true);
echo "1: ".($end - $start)."<br />\n";
unset($start, $end);
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if('foobar' == 10) {}
$end = microtime(true);
echo "2: ".($end - $start)."<br />\n";
unset($start, $end);
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if(5 === 10) {}
$end = microtime(true);
echo "3: ".($end - $start)."<br />\n";
unset($start, $end);
$start = microtime(true);
for($i = 0; $i < 100000000; $i++)
if('foobar' === 10) {}
$end = microtime(true);
echo "4: ".($end - $start)."<br />\n";
unset($start, $end);
?>
===================================
Result (depending on hardware configuration):
1: 16.779544115067
2: 21.305675029755
3: 16.345532178879
4: 15.991420030594
austinderrick2 at gmail dot com
03-Oct-2009 04:50
As an added note to the guy below, in such a case, use the !== operator like this.
$nkey = array_search($needle, $haystack);
if ($nkey !== false) { ...
The !== and the === compare the "types". So, with this type of comparision, 0 is not the same as the FALSE returned by the array_search array when it can not find a match. :)
Quoted Text:
===================================
Be careful with stuff like
if ($nkey = array_search($needle, $haystack)) { ...
if the returned key is actually the key 0, then the if won't be executed
===================================
jm+phpweb at roth dot lu
28-Aug-2009 02:25
Be careful with stuff like
if ($nkey = array_search($needle, $haystack)) { ...
if the returned key is actually the key 0, then the if won't be executed
strata_ranger at hotmail dot com
04-Apr-2009 05:13
Although most programmers are aware of this already, if for whatever reason you need to 'break' out of an if() block (which, unlike switch() is not considered a looping structure) just wrap it in an appropriate looping structure, such as a do-while(false):
<?php
do if ($foo)
{
// Do something first...
// Shall we continue with this block, or exit now?
if ($abort_if_block) break;
// Continue doing something...
} while (false);
?>
Anonymous
02-Apr-2009 04:32
If you need to do something when a function return FALSE and nothing when it return TRUE you can do it like that :
<?php
function call()
{
return FALSE;
}
if(call()==TRUE) // or if(call())
{
// nothing to do
}
else
{
// do something here
}
?>
You can also write it like this :
<?php
if(!call()==TRUE) // or if(!call())
{
// do something here
}
// here '!' will invert 'FALSE' (from call()) into 'TRUE'
?>
/!\ WARNING /!\
The '!' only work with booleans !
Check http://fr.php.net/manual/en/language.types.boolean.php to know if you can use '!'
If you want to compare two strings and use '!' be careful how you use it !!!!
<?php
$string1 = "cake";
$string2 = "foo";
if(!$string1==$string2)
{
echo "cake is a lie";
}
//this will ALWAYS fail without exception because '!' is applied to $string1 and not to '$string1==$string2'
//to work, you have to do like this
if(!($string1==$string2))
{
echo "cake is a lie";
}
//it will display 'cake is a lie' because ($string1==$string2) return FALSE and '!' will invert it into TRUE
?>
For array/float, it's the same !
contact at bsorin dot romania
07-Mar-2009 08:28
This has got the better part of my last 2 hours, so I'm putting it here, maybe it will save someone some time.
I had a
if (function1() && function2())
statement. Before returning true or false, function1() and function2() had to output some text. The trick is that, if function1() returns false, function2() is not called at all. It seems I should have known that, but it slipped my mind.
Anonymous
28-Sep-2008 05:03
Re : henryk dot kwak at gmail dot com
<?php function message($m)
{
echo "$m <br />\r";
return true;
}
$k=false;
if (message("first")&& $k && message("second")){;}
// will show
//first
class
$k=true;
if (message("first")&& $k && message("second")){;}
// will show
//first
//second
?>
john
24-Sep-2008 08:24
@henryk (and everybody):
You should put your arguments in order by *least* likely to be true. That way if php is going to be able to quit checking, it will happen sooner rather than later, and your script will run (what amounts to unnoticeably) faster.
At least, that makes the most sense to me, but I don't claim omniscience.
Wiseguy
28-Aug-2008 07:22
RE: chrislabricole at yahoo dot fr on 09-Aug-2008 05:53
You're referring to the ternary operator.
http://php.net/manual/en/language.operators.comparison.php
jchau at bu dot edu
14-Aug-2008 10:50
RE: henryk dot kwak at gmail dot com's comment from 04-May-2008 05:01
I think you made a mistake.
For maximum efficiency, assuming each expression requires the same amount of processing, the expression that is least likely to be true should come first for expressions connected by && (and). This will reduce the probability that later expressions will need to be evaluated.
The opposite is true for || (or). If the most likely expression comes first, then the probability of needing to evaluate later expressions is reduced.
chrislabricole at yahoo dot fr
09-Aug-2008 05:53
You can do IF with this pattern :
<?php
$var = TRUE;
echo $var==TRUE ? 'TRUE' : 'FALSE'; // get TRUE
echo $var==FALSE ? 'TRUE' : 'FALSE'; // get FALSE
?>
henryk dot kwak at gmail dot com
04-May-2008 05:01
When you use if command with many condidions like
if ( expr1 && expr2 && expr3 && etc. )
it is more effective to put expressions in special order
Firstly you should put that, which has the biggest
probability to occur.
This is because PHP checks each condition in order from left to right and it takes some time to check each condition.
grawity at gmail dot com
10-Mar-2008 03:41
re: #80305
Again useful for newbies:
if you need to compare a variable with a value, instead of doing
<?php
if ($foo == 3) bar();
?>
do
<?php
if (3 == $foo) bar();
?>
this way, if you forget a =, it will become
<?php
if (3 = $foo) bar();
?>
and PHP will report an error.
redrobinuk at aol dot com
09-Jan-2008 02:54
This is aimed at PHP beginners but many of us do this Ocasionally...
When writing an if statement that compares two values, remember not to use a single = statement.
eg:
<?php
if ($a = $b)
{
print("something");
}
?>
This will assign $a the value $b and output the statement.
To see if $a is exactly equal to $b (value not type) It should be:
<?php
if ($a == $b)
{
print("something");
}
?>
Simple stuff but it can cause havok deep in classes/functions etc...