Booleans

This is the easiest type. A boolean expresses a truth value. It can be either TRUE or FALSE.

Note: The boolean type was introduced in PHP 4.

Syntax

To specify a boolean literal, use either the keyword TRUE or FALSE. Both are case-insensitive.


<?php

$foo = True; // assign the value TRUE to $foo

?>

Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.


<?php

// == is an operator which test

// equality and returns a boolean

if ($action == "show_version") {

    echo "The version is 1.23";

}



// this is not necessary...

if ($show_separators == TRUE) {

    echo "<hr>\n";

}



// ...because you can simply type

if ($show_separators) {

    echo "<hr>\n";

}

?>

To explicitly convert a value to boolean, use either the (bool) or the (boolean) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.

See also Type Juggling.

When converting to boolean, the following values are considered FALSE:

the boolean FALSE itself
the integer 0 (zero)
the float 0.0 (zero)
the empty string, and the string "0"
an array with zero elements
an object with zero member variables (PHP 4 only)
the special type NULL (including unset variables)

Every other value is considered TRUE (including any resource).

Warning

-1 is considered TRUE, like any other non-zero (whether negative or positive) number!


<?php

var_dump((bool) "");        // 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
Booleans

bioster at peri dot csclub dot uwaterloo dot ca
18-Nov-2004 05:06


If you're *really* concerned with squeezing the most speed out of your code as possible (such as in a highly recursive section), you want to set your boolean style variables to 0 for false and 1 for true.  I've been doing benchmarks and I've found that these are the fastest.



Of course, these operations are so fast that you should only be concerned about the difference when you're iterating over a million or more of these operations.  (We're talking .02 seconds difference with a million iterations on my home machine.)

x123 (at) bestof (dash) inter (dot) net
15-Nov-2004 03:24


another correction to the preceding "correction":

"as the documention states" is right,

"any non-empty string is true" is wrong : (bool) "0" === false !

(but "00" and "0.0" etc. are true!)



So watch out, you can NOT test for non-empty strings using e.g.



<?php

if (is_string($s))

  if ($s) echo " '$s' is a non-empty string";

  else echo " '$s' is an empty string"; // wrong for $s='0' !

else echo " $s is not a string ";

?>



indeed, for $s='0' this would print: " '0' is an empty string"

which is wrong, of course.

This is particularly "dangerous" in connection with MySQL

which prints FALSE by default as 0,

which comes back from a FORM POST as string '0',

while PHP prints FALSE as empty string (!);

a similar problem is to preserve a NULL value through a FORM post....

adama at NO-UBE dot augustinefam dot org
23-May-2003 01:13


Just a correction to the 29-Apr-2003 10:49 posting. The first section of the comment, where



 $myBool = true ;  print( $myBool ) ;

 is indistinguishable from

 print( "" ) ;

 likewise,

 $myBool = false ; print( $myBool ) ;

 is indistinguishable from

 print( 1 ) ;



is backwards. It should actually be 



 $myBool = true ;  print( $myBool ) ;

 is indistinguishable from

 print( 1 ) ; //corrected

 likewise,

 $myBool = false ; print( $myBool ) ;

 is indistinguishable from

 print( "" ) ; //corrected



The posting makes a good point, though. Don't expect the contents of a string to mean something special. As the documentation states, any non-empty string is true, including "false" since it is simply a non-empty string.

discord at spambegone dot mac dot com
05-May-2003 03:37


/* Automatic boolean conversion in php is in line

    with most other programming languages. However,

    sometimes you may need more flexiblity with the

    type conversion. Here's an easy way:



      Say you want the user to be able to type

    any affirmative or negative and have it

    recognised as a boolean... you might do this:

*/



$bool = strtolower($_GET['user_response']);



$bool = ($bool=='yes' or $bool=='true'   or $bool=='correct'

       or $bool=='on'  or $bool=='right'  or $bool=='positive'

       or $bool=='yup' or $bool=='uh-huh' or $bool=='sure'

       or $bool===true);



/* this will set it to true if any of these strings

    are entered, or if it's already true; otherwise,

    it converts it to false. Note the triple equal sign

    when comparing it to the unquoted boolean true:

    this is the "exactly equal to" operator, which

      checks not just for equality, but for type. Using it 

    ensures that $bool doesn't get converted to a boolean

    for the comparison: $bool===true is only true 

    if $bool is a true boolean, whereas $bool==true

    is true for any non-empty string (except "0").

*/

Booleans

Syntax

Converting to boolean