PHP 자료형 비교표

다음 테이블은 PHP 자료형 과 느슨한 비교와 엄격한 비교를 위한 비교 연산자의 동작을 설명한다. 이 부록은 자료형 조절에 관한 매뉴얼 섹션과도 관련이 있다. 다양한 유저 주석과 » BlueShoes의 보고서를 통해 영감을 얻을수 있다.

이 테이블을 이용하기 전에, 자료형과 각 자료형의 의미를 이해해야 한다. 예를 들면, "42"string형이고, 반면에 42integer형이다. FALSEboolean형이고, "false"string형이 되는것이다.

Note:

HTML 폼은 정수, 부동소수점, 논리형으로 전달하지 않는다. 문자열형으로 전달한다. 문자열이 숫자값인지 확인하기 위해서는 is_numeric()를 사용할수 있다.

Note:

$x가 선언되지 않았는데 단순히 if ($x)를 수행하면 E_NOTICE 레벨의 에러가 발생할것이다. 대신 empty()isset()을 사용하고 그 변수를 초기화시키도록 한다.

PHP 함수로 $x 비교하기
Expression gettype() empty() is_null() isset() boolean : if($x)
$x = ""; string TRUE FALSE TRUE FALSE
$x = null; NULL TRUE TRUE FALSE FALSE
var $x; NULL TRUE TRUE FALSE FALSE
$x is undefined NULL TRUE TRUE FALSE FALSE
$x = array(); array TRUE FALSE TRUE FALSE
$x = false; boolean TRUE FALSE TRUE FALSE
$x = true; boolean FALSE FALSE TRUE TRUE
$x = 1; integer FALSE FALSE TRUE TRUE
$x = 42; integer FALSE FALSE TRUE TRUE
$x = 0; integer TRUE FALSE TRUE FALSE
$x = -1; integer FALSE FALSE TRUE TRUE
$x = "1"; string FALSE FALSE TRUE TRUE
$x = "0"; string TRUE FALSE TRUE FALSE
$x = "-1"; string FALSE FALSE TRUE TRUE
$x = "php"; string FALSE FALSE TRUE TRUE
$x = "true"; string FALSE FALSE TRUE TRUE
$x = "false"; string FALSE FALSE TRUE TRUE

==로 느슨한 비교
TRUE FALSE 1 0 -1 "1" "0" "-1" NULL array() "php" ""
TRUE TRUE FALSE TRUE FALSE TRUE TRUE FALSE TRUE FALSE FALSE TRUE FALSE
FALSE FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE TRUE TRUE FALSE TRUE
1 TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
0 FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE TRUE FALSE TRUE TRUE
-1 TRUE FALSE FALSE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
"1" TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
"0" FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE
"-1" TRUE FALSE FALSE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
NULL FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE TRUE FALSE TRUE
array() FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE TRUE TRUE FALSE FALSE
"php" TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE
"" FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE FALSE FALSE TRUE

===로 엄격한 비교
TRUE FALSE 1 0 -1 "1" "0" "-1" NULL array() "php" ""
TRUE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
1 FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
0 FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
-1 FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
"1" FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
"0" FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE
"-1" FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
NULL FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE
array() FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE
"php" FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE
"" FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE

add a note add a note

User Contributed Notes 15 notes

up
27
php at richardneill dot org
2 years ago
Be wary of string-comparison where both strings might be interpreted as numbers.  Eg:

$x="123456789012345678901234567890"; $y="123456789012345678900000000000";
echo  ($x==$y)?"equal":"not_equal";   #Prints equal !!

Both strings are getting converted to floats, then losing precision, then becoming equal :-(

Using "===" or making either of the strings non-numeric will prevent this.
[This is on a 32-bit machine, on a 64-bit, you will have to make the strings longer to see the effect]
up
10
frank
7 years ago
A comparison table for <=,<,=>,> would be nice...
Following are TRUE (tested PHP4&5):
NULL <= -1
NULL <= 0
NULL <= 1
!(NULL >= -1)
NULL >= 0
!(NULL >= 1)
That was a surprise for me (and it is not like SQL, I would like to have the option to have SQL semantics with NULL...).
up
6
aidan at php dot net
9 years ago
The way PHP handles comparisons when multiple types are concerned is quite confusing.

For example:
"php" == 0

This is true, because the string is casted interally to an integer. Any string (that does not start with a number), when casted to an integer, will be 0.
up
6
edgar at goodforall dot eu
4 years ago
Some function to write out your own comparisson table in tsv format. Can be easily modified to add more testcases and/or binary functions. It will test all comparables against each other with all functions.

<?php
$funcs
= array(
       
/* Testing equality */
       
'eq' => '==',
       
'ne' => '!=',
       
'gt' => '>',
       
'lt' => '<',
       
'ne2' => '<>',
       
'lte' => '<=',
       
'gte' => '>=',
       
/* Testing identity */
       
'id' => '===',
       
'nid' => '!=='
);
class
Test {
        protected
$a;
        public
$b;
        public function
__construct($a,$b){
               
$this->a = $a;
               
$this->b = $b;
        }
        public function
getab(){
                return
$this->a.",". $this->b;
        }

}
$tst1 = new Test(1,2);
$tst2 = new Test(1,2);
$tst3 = new Test(2,2);
$tst4 = new Test(1,1);

$arr1 = array(1,2,3);
$arr2 = array(2,3,4);
$arr3 = array('a','b','c','d');
$arr4 = array('a','b','c');
$arr5 = array();

$comp1 = array(
       
'ints' => array(-1,0,1,2),
       
'floats' => array(-1.1,0.0,1.1,2.0),
       
'string' => array('str', 'str1', '', '1'),
       
'bools' => array(true, false),
       
'null' => array(null),
       
'objects' => array($tst1,$tst2,$tst3,$tst4),
       
'arrays' => array($arr1, $arr2, $arr3, $arr4, $arr5)
);
$fbody = array();

foreach(
$funcs as $name => $op){
       
$fbody[$name] = create_function('$a,$b', 'return $a ' . $op . ' $b;');
}

$table = array(array('function', 'comp1', 'comp2', 'f comp1 comp2', 'type'));
/* Do comparisons */
$comp2  = array();
foreach(
$comp1 as $type => $val){
       
$comp2[$type] = $val;
}

foreach(
$comp1 as $key1 => $val1){
        foreach(
$comp2 as $key2 => $val2){
               
addTableEntry($key1, $key2, $val1, $val2);
        }
}
$out = '';
foreach(
$table as $row){
       
$out .= sprintf("%-20s\t%-20s\t%-20s\t%-20s\t%-20s\n", $row[0], $row[1], $row[2], $row[3], $row[4]);
}

print
$out;
exit;

function
addTableEntry($n1, $n2, $comp1, $comp2){
        global
$table, $fbody;
        foreach(
$fbody as $fname => $func){
                        foreach(
$comp1 as $val1){
  foreach(
$comp2 as $val2){
                                       
$val = $func($val1,$val2);
                                               
$table[] = array($fname, gettype($val1) . ' => ' . sprintval($val1), gettype($val2) .' => ' . sprintval($val2), gettype($val) . ' => ' . sprintval($val), gettype($val1) . "-" . gettype($val2) . '-' . $fname);
                                        }
                        }
        }
}

function
sprintval($val){
        if(
is_object($val)){
                return
'object-' . $val->getab();
        }
        if(
is_array($val)){
                return
implode(',', $val);
        }
        if(
is_bool($val)){
                if(
$val){
                        return
'true';
                }
                return
'false';
        }
        return
strval($val);
}

?>
up
4
php at benizi dot com
4 years ago
It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
up
7
Jan
8 years ago
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
up
5
jerryschwartz at comfortable dot com
9 years ago
In some languages, a boolean is promoted to an integer (with a value of 1 or -1, typically) if used in an expression with an integer. I found that PHP has it both ways:

If you add a boolean with a value of true to an integer with a value of 3, the result will be 4 (because the boolean is cast as an integer).

On the other hand, if you test a boolean with a value of true for equality with an integer with a value of three, the result will be true (because the integer is cast as a boolean).

Surprisingly, at first glance, if you use either < or > as the comparison operator the result is always false (again, because the integer as cast as a boolean, and true is neither greater nor less than true).
up
3
crazy888s at hotmail dot com
1 year ago
PHP's loose comparisons can be a huge convenience when used properly! It's extremely helpful to just remember the following are always FALSE:

null, false, "", 0, "0", array()

If your application never depends on a particular "empty/false/null/0/not set" value type, you won't have to worry about 99% of the other weird cases listed here. You won't need empty() or isset(). And ALL variable types will always work as expected for statements like:

if(boolean && !string){...}
if(array){...}
if(!null || int){...}

Consider the same when working with your database values.
up
2
info at shaelf dot ru
6 years ago
Compare object
<?php
$o
= new stdClass();
$o->we = 12;

$o2 = new stdClass();
$o2->we = 12;

$o3 = clone $o2;
var_dump($o == $o2); //true
var_dump($o === $o2); //false
var_dump($o3 === $o2); //true
?>
up
1
tom
9 years ago
<?php
if (strlen($_POST['var']) > 0) {
   
// form value is ok
}
?>

When working with HTML forms this a good way to:

(A) let "0" post values through like select or radio values that correspond to array keys or checkbox booleans that would return FALSE with empty(), and;
(B) screen out $x = "" values, that would return TRUE with isset()!

Because HTML forms post values as strings, this is a good way to test variables!

[[Editor Note: This will create a PHP Error of level E_NOTICE if the checked variable (in this case $_POST['var']) is undefined. It may be used after (in conjuection with) isset() to prevent this.]]
up
1
Anonymous
1 month ago
The loose comparison chart is missing a few things.

array(1)==true returns true.

also:

(int)array(1) === 1 returns true

This is symmetric:

array(1) === (array)1 returns true

but the loose comparison

array(1)==1 still returns false.
up
0
blue dot hirano at gmail dot com
2 months ago
The truth tables really ought to be colorized; they're very hard to read as they are right now (just big arrays of TRUE and FALSE).

Also, something to consider: clustering the values which compare similarly (like is done on qntm.org/equality) would make the table easier to read as well. (This can be done simply by hand by rearranging the order of headings to bring related values closer together).
up
-1
Anonymous
1 year ago
I'm running PHP 5.5.3.

This is a correction to one of the previous posts.

<?php
$o
= new stdClass();
$o->we = 12;

$o2 = new stdClass();
$o2->we = 12;

$o3 = clone $o2;
var_dump($o == $o2); //true
var_dump($o === $o2); //false
var_dump($o3 === $o2); //false
?>

Output is:

true, false, false
up
-7
Jouriy LYSENKO
3 years ago
If $var not declared.

In php 5.2 :
<?php if($var) ?> - work

in php 5.3 :
<?php if($var) ?> - dont work and generate error E_NOTICE
up
-6
lorenzo dot campagna at ymail dot com
10 months ago
Someone can explain why this comparison result TRUE  when it should be FALSE?

<?php

$a
= "3abcdef";
$b = 3;

if(
$a == $b) {print("Match!");}    //Because of this comparison TRUE script will output:

?>
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