How to convert string to boolean php

This method was posted by @lauthiamkok in the comments. I'm posting it here as an answer to call more attention to it.

Depending on your needs, you should consider using filter_var() with the FILTER_VALIDATE_BOOLEAN flag.

filter_var(      true, FILTER_VALIDATE_BOOLEAN); // true
filter_var(    'true', FILTER_VALIDATE_BOOLEAN); // true
filter_var(         1, FILTER_VALIDATE_BOOLEAN); // true
filter_var(       '1', FILTER_VALIDATE_BOOLEAN); // true
filter_var(      'on', FILTER_VALIDATE_BOOLEAN); // true
filter_var(     'yes', FILTER_VALIDATE_BOOLEAN); // true

filter_var(     false, FILTER_VALIDATE_BOOLEAN); // false
filter_var(   'false', FILTER_VALIDATE_BOOLEAN); // false
filter_var(         0, FILTER_VALIDATE_BOOLEAN); // false
filter_var(       '0', FILTER_VALIDATE_BOOLEAN); // false
filter_var(     'off', FILTER_VALIDATE_BOOLEAN); // false
filter_var(      'no', FILTER_VALIDATE_BOOLEAN); // false
filter_var('asdfasdf', FILTER_VALIDATE_BOOLEAN); // false
filter_var(        '', FILTER_VALIDATE_BOOLEAN); // false
filter_var(      null, FILTER_VALIDATE_BOOLEAN); // false

The String "false" is actually considered a "TRUE" value by PHP. The documentation says:

To explicitly convert a value to boolean, use the (bool) or (boolean) casts. However, in most cases the cast is unnecessary, 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)

• SimpleXML objects created from empty tags

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

so if you do:

$bool = (boolean)"False";

or

$test = "false";
$bool = settype($test, 'boolean');

in both cases $bool will be TRUE. So you have to do it manually, like GordonM suggests.

When working with JSON, I had to send a Boolean value via $_POST. I had a similar problem when I did something like:

if ( $_POST['myVar'] == true) {
    // do stuff;
}

In the code above, my Boolean was converted into a JSON string.

To overcome this, you can decode the string using json_decode():

//assume that : $_POST['myVar'] = 'true';
 if( json_decode('true') == true ) { //do your stuff; }

(This should normally work with Boolean values converted to string and sent to the server also by other means, i.e., other than using JSON.)

you can use json_decode to decode that boolean

$string = 'false';
$boolean = json_decode($string);
if($boolean) {
  // Do something
} else {
  //Do something else
}

(boolean)json_decode(strtolower($string))

It handles all possible variants of $string

'true'  => true
'True'  => true
'1'     => true
'false' => false
'False' => false
'0'     => false
'foo'   => false
''      => false

filter_var($string, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);

$string = 1; // true
$string ='1'; // true
$string = 'true'; // true
$string = 'trUe'; // true
$string = 'TRUE'; // true
$string = 0; // false
$string = '0'; // false
$string = 'false'; // false
$string = 'False'; // false
$string = 'FALSE'; // false
$string = ''; // false
$string = 'sgffgfdg'; // null

You must specify

FILTER_NULL_ON_FAILURE

If your "boolean" variable comes from a global array such as $_POST and $_GET, you can use filter_input() filter function.

Example for POST:

$isSleeping  = filter_input(INPUT_POST, 'is_sleeping',  FILTER_VALIDATE_BOOLEAN);

If your "boolean" variable comes from other source you can use filter_var() filter function.

Example:

filter_var('true', FILTER_VALIDATE_BOOLEAN); // true

the easiest thing to do is this:

$str = 'TRUE';

$boolean = strtolower($str) == 'true' ? true : false;

var_dump($boolean);

Doing it this way, you can loop through a series of 'true', 'TRUE', 'false' or 'FALSE' and get the string value to a boolean.

Other answers are over complicating things. This question is simply logic question. Just get your statement right.

$boolString = 'false';
$result = 'true' === $boolString;

Now your answer will be either

• false, if the string was 'false',
• or true, if your string was 'true'.

I have to note that filter_var( $boolString, FILTER_VALIDATE_BOOLEAN ); still will be a better option if you need to have strings like on/yes/1 as alias for true.

function stringToBool($string){
    return ( mb_strtoupper( trim( $string)) === mb_strtoupper ("true")) ? TRUE : FALSE;
}

or

function stringToBool($string) {
    return filter_var($string, FILTER_VALIDATE_BOOLEAN);
}

I do it in a way that will cast any case insensitive version of the string "false" to the boolean FALSE, but will behave using the normal php casting rules for all other strings. I think this is the best way to prevent unexpected behavior.

$test_var = 'False';
$test_var = strtolower(trim($test_var)) == 'false' ? FALSE : $test_var;
$result = (boolean) $test_var;

Or as a function:

function safeBool($test_var){
    $test_var = strtolower(trim($test_var)) == 'false' ? FALSE : $test_var;
    return (boolean) $test_var;
}

The answer by @GordonM is good. But it would fail if the $string is already true (ie, the string isn't a string but boolean TRUE)...which seems illogical.

Extending his answer, I'd use:

$test_mode_mail = ($string === 'true' OR $string === true));

I was getting confused with wordpress shortcode attributes, I decided to write a custom function to handle all possibilities. maybe it's useful for someone:

function stringToBool($str){
    if($str === 'true' || $str === 'TRUE' || $str === 'True' || $str === 'on' || $str === 'On' || $str === 'ON'){
        $str = true;
    }else{
        $str = false;
    }
    return $str;
}
stringToBool($atts['onOrNot']);

$string = 'false';

$test_mode_mail = $string === 'false' ? false : true;

var_dump($test_mode_mail);

if($test_mode_mail) echo 'test mode is on.';

You have to do it manually

You can use the settype method too!

$string = 'false';
$boolean = settype($string,"boolean");
var_dump($boolean); //see 0 or 1

Another solution in php-8 could be:

function convertToBool(string $value): bool
{
     return match($value) {
         'true' => true,
         default => false,
     };
}

A simple way is to check against an array of values that you consider true.

$wannabebool = "false";
$isTrue = ["true",1,"yes","ok","wahr"];
$bool = in_array(strtolower($wannabebool),$isTrue);

Edited to show a working solution using preg_match(); to return boolean true or false based on a string containing true. This may be heavy in comparison to other answers but can easily be adjusted to fit any string to boolean need.

$test_mode_mail = 'false';      
$test_mode_mail = 'true'; 
$test_mode_mail = 'true is not just a perception.';

$test_mode_mail = gettype($test_mode_mail) !== 'boolean' ? (preg_match("/true/i", $test_mode_mail) === 1 ? true:false):$test_mode_mail;

echo ($test_mode_mail === true ? 'true':'false')." ".gettype($test_mode_mail)." ".$test_mode_mail."<br>";