## Booléen

C'est le type le plus simple. Un bool représente une valeur de vérité. Il peut valoir `true` ou `false`.

### Syntaxe

Pour spécifier un booléen littéral, utilisez la constante `true` ou `false`. Les deux sont insensibles à la casse.

``` <?php\$foo = true; // assigne la valeur TRUE à \$foo?> ```

Typiquement, le résultat d'un opérateur qui retourne un booléen, passé ensuite à une structure de contrôle.

``` <?php// == est un opérateur qui teste// l'égalité et retourne un booléenif (\$action == "show_version") {    echo "La version est 1.23";}// ceci n'est pas nécessaire...if (\$show_separators == TRUE) {    echo "<hr>\n";}// ...à la place, vous pouvez utiliser, avec la même signification :if (\$show_separators) {    echo "<hr>\n";}?> ```

### Conversion en booléen

Pour convertir explicitement une valeur en booléen, utilisez `(bool)` ou `(boolean)`. Cependant, dans la plupart des cas, le transtypage n'est pas nécessaire, sachant qu'une valeur sera automatiquement convertie si un opérateur, une fonction ou une structure de contrôle demandent un argument de type booléen.

Voir aussi le transtypage.

Lors d'une conversion en booléen, les valeurs suivantes sont considérées comme `false` :

Toutes les autres valeurs sont considérées comme `true` (y compris toutes les ressources et `NAN`).

Avertissement

`-1` est considéré comme `true`, comme tous les nombres différents de zéro (négatifs ou positifs) !

``` <?phpvar_dump((bool) "");        // bool(false)var_dump((bool) "0");       // bool(false)var_dump((bool) 1);         // bool(true)var_dump((bool) -2);        // bool(true)var_dump((bool) "foo");     // bool(true)var_dump((bool) 2.3e5);     // bool(true)var_dump((bool) array(12)); // bool(true)var_dump((bool) array());   // bool(false)var_dump((bool) "false");   // bool(true)?> ```

### User Contributed Notes 24 notes

898
Fred Koschara
9 years ago
``` Ah, yes, booleans - bit values that are either set (TRUE) or not set (FALSE).  Now that we have 64 bit compilers using an int variable for booleans, there is *one* value which is FALSE (zero) and 2**64-1 values that are TRUE (everything else).  It appears there's a lot more truth in this universe, but false can trump anything that's true...PHP's handling of strings as booleans is *almost* correct - an empty string is FALSE, and a non-empty string is TRUE - with one exception:  A string containing a single zero is considered FALSE.  Why?  If *any* non-empty strings are going to be considered FALSE, why *only* a single zero?  Why not "FALSE" (preferably case insensitive), or "0.0" (with how many decimal places), or "NO" (again, case insensitive), or ... ?The *correct* design would have been that *any* non-empty string is TRUE - period, end of story.  Instead, there's another GOTCHA for the less-than-completely-experienced programmer to watch out for, and fixing the language's design error at this late date would undoubtedly break so many things that the correction is completely out of the question.Speaking of GOTCHAs, consider this code sequence:<?php\$x=TRUE;\$y=FALSE;\$z=\$y OR \$x;?>Is \$z TRUE or FALSE?In this case, \$z will be FALSE because the above code is equivalent to <?php (\$z=\$y) OR \$x ?> rather than <?php \$z=(\$y OR \$x) ?> as might be expected - because the OR operator has lower precedence than assignment operators.On the other hand, after this code sequence:<?php\$x=TRUE;\$y=FALSE;\$z=\$y || \$x;?>\$z will be TRUE, as expected, because the || operator has higher precedence than assignment:  The code is equivalent to \$z=(\$y OR \$x).This is why you should NEVER use the OR operator without explicit parentheses around the expression where it is being used. ```
127
Mark Simon
5 years ago
``` Note for JavaScript developers:In PHP, an empty array evaluates to false, while in JavaScript an empty array evaluates to true.In PHP, you can test an empty array as <?php if(!\$stuff) …; ?> which won’t work in JavaScript where you need to test the array length.This is because in JavaScript, an array is an object, and, while it may not have any elements, it is still regarded as something.Just a trap for young players who routinely work in both langauges. ```
14
asma dot gi dot 14 at gmail dot com
1 year ago
``` Please keep in mind that the result of  0 == 'whatever'  is true in PHP Version 7 and false in PHP version 8. ```
148
13 years ago
``` Beware of certain control behavior with boolean and non boolean values :<?php// Consider that the 0 could by any parameters including itselfvar_dump(0 == 1); // falsevar_dump(0 == (bool)'all'); // falsevar_dump(0 == 'all'); // TRUE, take carevar_dump(0 === 'all'); // false// To avoid this behavior, you need to cast your parameter as string like that :var_dump((string)0 == 'all'); // false?> ```
74
goran77 at fastmail dot fm
5 years ago
``` Just something that will probably save time for many new developers: beware of interpreting FALSE and TRUE as integers. For example, a small function for deleting elements of an array may give unexpected results if you are not fully aware of what happens: <?phpfunction remove_element(\$element, \$array){   //array_search returns index of element, and FALSE if nothing is found   \$index = array_search(\$element, \$array);   unset (\$array[\$index]);   return \$array; }// this will remove element 'A'\$array = ['A', 'B', 'C'];\$array = remove_element('A', \$array);//but any non-existent element will also remove 'A'!\$array = ['A', 'B', 'C'];\$array = remove_element('X', \$array);?>The problem here is, although array_search returns boolean false when it doesn't find specific element, it is interpreted as zero when used as array index.So you have to explicitly check for FALSE, otherwise you'll probably loose some elements:<?php//correctfunction remove_element(\$element, \$array){   \$index = array_search(\$element, \$array);   if (\$index !== FALSE)    {       unset (\$array[\$index]);   }   return \$array; } ```
54
terminatorul at gmail dot com
15 years ago
``` Beware that "0.00" converts to boolean TRUE !You may get such a string from your database, if you have columns of type DECIMAL or CURRENCY. In such cases you have to explicitly check if the value is != 0 or to explicitly convert the value to int also, not only to boolean. ```
42
Steve
14 years ago
``` PHP does not break any rules with the values of true and false.  The value false is not a constant for the number 0, it is a boolean value that indicates false.  The value true is also not a constant for 1, it is a special boolean value that indicates true.  It just happens to cast to integer 1 when you print it or use it in an expression, but it's not the same as a constant for the integer value 1 and you shouldn't use it as one.  Notice what it says at the top of the page:A boolean expresses a truth value.It does not say "a boolean expresses a 0 or 1".It's true that symbolic constants are specifically designed to always and only reference their constant value.  But booleans are not symbolic constants, they are values.  If you're trying to add 2 boolean values you might have other problems in your application. ```
36
artktec at gmail dot com
14 years ago
``` Note you can also use the '!' to convert a number to a boolean, as if it was an explicit (bool) cast then NOT.So you can do something like:<?php\$t = !0; // This will === true;\$f = !1; // This will === false;?>And non-integers are casted as if to bool, then NOT.Example:<?php\$a = !array();      // This will === true;\$a = !array('a');   // This will === false;\$s = !"";           // This will === true;\$s = !"hello";      // This will === false;?>To cast as if using a (bool) you can NOT the NOT with "!!" (double '!'), then you are casting to the correct (bool).Example:<?php\$a = !!array();   // This will === false; (as expected)/* This can be a substitute for count(\$array) > 0 or !(empty(\$array)) to check to see if an array is empty or not  (you would use: !!\$array).*/\$status = (!!\$array ? 'complete' : 'incomplete');\$s = !!"testing"; // This will === true; (as expected)/* Note: normal casting rules apply so a !!"0" would evaluate to an === false*/?> ```
11
Mark Simon
5 years ago
``` Note on the OR operator.A previous comment notes the trap you can fall into with this operator. This is about its usefulness.Both OR and || are short-circuited operators, which means they will stop evaluating once they reach a TRUE value. By design, OR is evaluated after assignment (while || is evaluated before assignment).This has the benefit of allowing some simple constructions such as:<?php    \$stuff=getStuff() or die('oops');    \$thing=something() or \$thing=whatever();?>The first example, often seen in PERL, could have been written as <?php if(!\$stuff=getStuff()) die('oops'); ?> but reads a little more naturally. I have often used it in situations where null or false indicate failure.The second allows for an alternative value if a falsy one is regarded as insufficient. The following example<?php    \$page=@\$_GET['page'] or \$page=@\$_COOKIE['page'] or \$page=1;?>is a simple way sequencing alternative values. (Note the usual warnings about using the @ operator or accepting unfiltered input …)All this presupposes that 0 is also an unacceptable value in the situation. ```
31
Wackzingo
14 years ago
``` It is correct that TRUE or FALSE should not be used as constants for the numbers 0 and 1. But there may be times when it might be helpful to see the value of the Boolean as a 1 or 0. Here's how to do it. <?php \$var1 = TRUE; \$var2 = FALSE; echo \$var1; // Will display the number 1 echo \$var2; //Will display nothing /* To get it to display the number 0 for a false value you have to typecast it: */ echo (int)\$var2; //This will display the number 0 for false. ?> ```
marklgr
6 years ago
``` For those wondering why the string "0" is falsy, consider that a good deal of input data is actually string-typed, even when it is semantically numeral.PHP often tries to autoconvert these strings to numeral, as the programmer certainly intended (try 'echo "2"+3'). Consequently, PHP designers decided to treat 0 and "0" similarly, ie. falsy, for consistency and to avoid bugs where the programmer believes he got a true numeral that would happen to be truthy when zero. ```
richie dot hayward at gmail dot com
6 years ago
``` Actually from a complete noob point of view 0 resulting in false makes sense as many languages as I have been taught consider the value 1 as true and the value 0 as false a simple boolean value. So lets says you think you set a variable to 0 and some how or another through your code this value has implicitly become and string instead of a int or boolean. Should PHP now consider it to evaluate to false. I wouldn't think so but hey I'm a PHP noob so perhaps I'm missing why you would ever want a "0" string to evaluate to true. ```
geza at turigeza dot com
9 years ago
``` // someKey is a boolean true\$array = array('someKey'=>true);// in the following 'false' string gets converted to a boolean trueif(\$array['someKey'] != 'false')    echo 'The value of someKey is '.\$array['someKey'];As a result the above will output nothing :) if(\$array['someKey'] == 'false')    echo 'The value of someKey is '.\$array['someKey'];And the above will outputThe value of someKey is 1In short true == 'false' is true. ```
mike652638 at qq dot com
1 year ago
``` // For those newbies who may also have puzzles as following:  \$bool_val = (bool)true;  echo \$bool_val;  // Codes above prints 1  \$bool_val2 = (bool)false;  echo \$bool_val2;  // Codes above prints nothing (literally nothing)  // But how to print false or 0 (instead of nothing) for the falsy value or condition then ?  // Solution1:  \$bool_exp1 = (bool)false;  echo \$bool_exp1 ? 'true' : 'false';  // Codes above prints false;  // Solution2:  \$bool_exp2 = (bool)false;  echo json_encode(\$bool_exp2);  // Codes above prints false;  // Solution3:  \$bool_exp3 = (bool)false;  echo var_export(\$bool_exp3);  // Codes above prints false;  // Soluton4:  \$bool_exp4 = (bool)false;  echo (int)\$bool_exp4;  // Codes above prints 0;  // Solution5:  \$bool_exp5 = (bool)false;  var_dump(\$bool_exp5);  // Codes above prints bool(false); ```
fyrye at torntech dot com
12 years ago
``` Since I haven't seen it posted.Here is a function that you can use if you have a need to force strict boolean values.Hopefully this will save someone some time from searching for similar.<?phpfunction strictBool(\$val=false){    return is_integer(\$val)?false:\$val == 1;}?>Simply put, it verifies that the value passed is (bool)true otherwise it's false.Examples:__________________________________<?php\$myBool = strictBool(true);var_dump(\$myBool);//returns (bool)true\$myar = array(0 => true);\$myBool = strictBool(\$myar);var_dump(\$myBool);//returns (bool)true\$myBool = strictBool("hello");var_dump(\$myBool);//returns (bool)false\$myBool = strictBool(false);var_dump(\$myBool);//returns (bool)false\$myBool = strictBool(array(0 => "hello"));var_dump(\$myBool);//returns (bool)false\$myBool = strictBool(1);var_dump(\$myBool);//returns (bool)false\$myBool = strictBool();var_dump(\$myBool);//returns (bool)false?> ```
-1
asma dot gi dot 14 at gmail dot com
1 year ago
``` when using echo false; or print false; the display will be empty but when using echo 0; or print 0; the display will be 0. ```
-4
emanuelemicciulla[at]gmail[dot]com
7 years ago
``` A lot of people apparently looking for this:<?php\$strictBool = filter_var(\$stringBool, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);if(\$boolFanOvr === null) { /*manage error*/};?>it's TRUE for "true" "True" "TRUE" "Yes" "1" and so on.FALSE for "false" "0" "no" and so on.it's NULL if string doesn't represent a valid boolean. ```
-4
oscar at oveas dot com
11 years ago
``` Dunno if someone else posted this solution already, but if not, here's a useful and function to convert strings to strict booleans.Note this one only checks for string and defaults to the PHP (boolean) cast where e.g. -1 returns true, but you easily add some elseifs for other datatypes.<?phpfunction toStrictBoolean (\$_val, \$_trueValues = array('yes', 'y', 'true'), \$_forceLowercase = true){    if (is_string(\$_val)) {        return (in_array(             (\$_forceLowercase?strtolower(\$_val):\$_val)            , \$_trueValues)        );    } else {        return (boolean) \$_val;    }}?> ```
-7
Symbol
13 years ago
``` Just a side note, doesn't really matters, the reason -1 is true and not false is because boolean type is treated as unsigned, so -1 would be for example, if it's unsigned int32 translate to hex: 0xFFFFFFFF and back to decimal: 4294967295 which is non-zero. there isn't really a "negative boolean". it's a binary thing. :o (since it used to be a bit and then there was only 0 and 1 as an option) ```
-3
Anonymous
1 year ago
``` What will be the output you think if we add echo and print both at a time..<?php\$a = 5;print print \$a;  // prints out: 51     inner 'print' prints the value of \$a, then                                                                                                                                     // outer 'print' returns  the boolean true about print \$aecho print \$a;  // prints out: 51     inner 'print' prints the value of \$a, then // outer 'echo' returns  the boolean true about print \$aecho echo \$a;    // syntax error.. echo doesn't returnprint echo \$a;     // syntax error.. echo doesn't return?> ```
-16
mercusmaximus at yahoo dot com
12 years ago
``` Note that the comparison: (false == 0) evaluates to true and so will any value you set to false as well (without casting). ```
-22
wbcarts at juno dot com
13 years ago
``` CODING PRACTICE...Much of the confusion about booleans (but not limited to booleans) is the fact that PHP itself automatically makes a type cast or conversion for you, which may NOT be what you want or expect. In most cases, it's better to provide functions that give your program the exact behavior you want.<?phpfunction boolNumber(\$bValue = false) {                      // returns integer  return (\$bValue ? 1 : 0);}function boolString(\$bValue = false) {                      // returns string  return (\$bValue ? 'true' : 'false');}\$a = true;                                                  // boolean valueecho 'boolean \$a AS string = ' . boolString(\$a) . '<br>';   // boolean as a stringecho 'boolean \$a AS number = ' . boolNumber(\$a) . '<br>';   // boolean as a numberecho '<br>';\$b = (45 > 90);                                             // boolean valueecho 'boolean \$b AS string = ' . boolString(\$b) . '<br>';   // boolean as a stringecho 'boolean \$b AS number = ' . boolNumber(\$b) . '<br>';   // boolean as a numberecho '<br>';\$c = boolNumber(10 > 8) + boolNumber(!(5 > 10));            // adding booleansecho 'integer \$c = ' . \$c .'<br>';?>Results in the following being printed... boolean \$a AS string = true boolean \$a AS number = 1 boolean \$b AS string = false boolean \$b AS number = 0 integer \$c = 2In other words, if we know what we want out of our program, we can create functions to accommodate. Here, we just wanted 'manual control' over numbers and strings, so that PHP doesn't confuse us. ```
-13
``` First, this is very useful. Second, I want to ask about the example, how the following:var_dump((bool) "false");   // bool(true)Thanks in advance http://www.bu.edu.eg/staff/shadyelmashad3 ```
``` When compare zero (0) with string it's return true by type jugling. When compare with TRUE with also the same string it's also returning true. But when comparing zero (0) with True then it's returning FALSE. echo 0 == 'This is a string'; // 1echo TRUE == 'This is a string'; //1echo 0 == TRUE ; // FALSE ``` 