Test if string could be boolean PHP

Question

I'm getting a string from a $_GET and I want to test if it could be a boolean, before I use it for a part of a mysql query. Is there a better way of doing it than:

function checkBool($string){
    $string = strtolower($string);
    if ($string == "true" || $string == "false" || 
        $string == "1" || $string == "0"){
        return true;
    }
    else {
        return false;
    }
}

if (checkBool($_GET['male'])){
    $result = mysql_query(
        "SELECT * FROM my_table " .
        "WHERE male='".$_GET['male']."'") or die(mysql_error());
}

This won't work anyway. What is your column type for male? The MySQL boolean type is really just a tinyint(1) so if it's that then you should only check for 1s or 0s. If you're using char/varchar and have previously set it to "true" then comparing it with "yes" or "1" will still not match. — daiscog
– daiscog, Commented Nov 25, 2011 at 18:01
point taken for checking yes and no, edited my snippet accordingly. Column type is indeed tinyint(1)! so true, false, 1 and 0 is what I need to check for — DexCurl
– DexCurl, Commented Nov 25, 2011 at 18:12
@DexCurl, This doesn't really change anything. You'll still have to use your own function, rewrited as I answered below. — sh03
– sh03, Commented Nov 25, 2011 at 18:16
Checking for string equivalency won't work, though. Your SQL puts $_GET['male'] inside quote marks, so if $_GET['male'] was "true" you'd get SELECT * FROM my_table WHERE male='true'. This will actually return rows where male=0 because MySQL tries to convert the STRING "true" to a number but can't so it gives it the value 0. Take out the single quotes and it works as expected. — daiscog
– daiscog, Commented Nov 25, 2011 at 18:17
@daiscog, I believe you have NOT got the point of the question. — sh03
– sh03, Commented Nov 25, 2011 at 18:19

Your Common Sense · Accepted Answer · 2025-11-22 15:46:12Z

22

You can use filter_var() with FILTER_VALIDATE_BOOLEAN flag, like

<?php
$myString = "On";
$b = filter_var($myString, FILTER_VALIDATE_BOOLEAN);

However, it will return false for both false and incorrect values (which could be enough if all you need is to know whether input value is true. But if you need to truly validate the input value, consider using a function suggested in this answer to tell whether input value can be interpreted as boolean or not.

edited Nov 22 at 15:46

Your Common Sense

158k42 gold badges226 silver badges374 bronze badges

answered Nov 25, 2011 at 18:01

zrvan

7,8031 gold badge25 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Flukey Over a year ago

+1 i've been using php for years and i've never heard of this 'filter_var' function. cool! Although you have to be using php >= 5.2. thanks!

sh03 Over a year ago

This doesn't really solve anything. "False" will return false in both is_bool() and $b.

DexCurl Over a year ago

Thanks for your answer zrvan! is_bool() doesn't work with strings as tested by var_dump(is_bool("true")); and filter_var works nicely to transform something into a boolean answer, but I needed something to check if string is a boolean first

Álvaro González Over a year ago

is_bool() does work with strings: it always returns FALSE, which is the correct answer since strings are strings, not booleans ;-P

Magnar Myrtveit Over a year ago

@Shoe see my answer for how filter_var() can be used to validate strings like "False" and be a viable solution to the problem.

sh03 · Accepted Answer · 2015-05-04 17:33:13Z

11

There's, by the way, a cleaner way of writing it:

function checkBool($string){
    $string = strtolower($string);
    return (in_array($string, array("true", "false", "1", "0", "yes", "no"), true));
}

But yes. The one you wrote down is the only way.

edited May 4, 2015 at 17:33

answered Nov 25, 2011 at 18:05

sh03

76.5k39 gold badges177 silver badges282 bronze badges

6 Comments

DexCurl Over a year ago

Thanks for your Jeff, very nice way of doing it. Greatly appreciated!

daiscog Over a year ago

This might look neater but involves more overhead for PHP. It has to create an array, store it in the heap, then call another function which does the comparison. The original function is more efficient.

sh03 Over a year ago

@daiscog, seriously? How much does it cost more? 0.0000000000000000000000000001 nanosecond to perform 123456789 calls to that function? It will probably be near 3 minutes the time you'll need to figure out what that original function does.

daiscog Over a year ago

Haha, yeah I have this discussion a lot. But I think the original function is pretty clear and I'm one of the "every clock cycle counts" brigade, I'm afraid. Old fashioned, I suppose, but I think it all adds up, especially in big applications.

Matt Kantor Over a year ago

See my answer to another question for a more flexible (yet more verbose) solution. DexCurl should really be using parameterized queries, anyway.

|

Magnar Myrtveit · Accepted Answer · 2016-02-10 08:35:38Z

6

If you use the flag FILTER_NULL_ON_FAILURE, filter_var() will work nicely:

function CheckBool($Value) {
  return null !== filter_var($Value, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE);
}

answered Feb 10, 2016 at 8:35

Magnar Myrtveit

2,8003 gold badges35 silver badges61 bronze badges

Comments

Mathieu Dumoulin · Accepted Answer · 2011-11-25 17:59:32Z

2

No you got it, there isn't anything more you can do, you got all possible values that would normally be considered as true or false and you're doing the comparison the right way, you COULD optimize it using an IN_ARRAY maybe, but even so, i find this version quite good already.

answered Nov 25, 2011 at 17:59

Mathieu Dumoulin

12.3k7 gold badges47 silver badges71 bronze badges

Comments

DarkBee · Accepted Answer · 2025-11-22 11:37:33Z

2

Boolean variables contain true or false values. To test if string could be boolean, different approaches can be used:

is_bool($var): The function is_bool() checks whether a variable’s type is Boolean and returns true or false.
Comparison using “===” or ($var===true || $var===false): If you compare the variable with the operator “===” with true and false and if it is identical to one of the values, then it is a boolean value. Since the functionality of is_bool($var) is same, the function should be preferred.
Comparison using “==” or ($var == true || $var == false): If you use “==” as an operator instead, the test is more tolerant. For example, 0(integer) or “”(empty string) would also result in a Boolean value.

edited Nov 22 at 11:37

DarkBee

14.4k9 gold badges86 silver badges134 bronze badges

answered Jan 8, 2021 at 23:50

thomas

6319 silver badges7 bronze badges

Comments

Álvaro González · Accepted Answer · 2011-11-25 18:40:09Z

Your checkBool() is quite right, IMHO, though there's a problem with the resulting SQL code. You can use TRUE and FALSE, but you must be aware that they aren't strings:

The constants TRUE and FALSE evaluate to 1 and 0, respectively. The constant names can be written in any lettercase.

So where it says this:

"SELECT * FROM my_table WHERE male='".$_GET['male']."'"

... it should say this:

'SELECT * FROM my_table WHERE male='.$_GET['male']

It'd feel better if checkBool() was actually convertToBool() and you would feed your query with its result value rather than the original $_GET, but your code is not really wrong.

BTW, I'm assuming that you are using a BOOL column type. This is what the manual says:

These types are synonyms for TINYINT(1). A value of zero is considered false. Nonzero values are considered true

Of course, it's up to you whether to use BOOL, ENUM, CHAR(1) or anything else, as well as whether to accept 33 as synonym for TRUE ;-)

daiscog · Accepted Answer · 2011-11-25 18:29:24Z

0

For what it's worth, if you really wanted to accept "yes" or "no" as valid input from the user, then I'd do something like this:

function toBoolean($string){
    $string = strtolower($string);
    if ($string == "true" || $string == "1"|| $string == "yes" )
        return true;
    elseif ($string == "false" || $string == "0" || $string == "no")
        return false;
    else
        throw new Exception("You did not submit a valid value, you naughty boy");
}

try {
    $query = "SELECT * FROM my_table WHERE male=" . (toBoolean($_GET['male']) ? "1" : "0" );
    $result = mysql_query($query) or die(mysql_error());
} catch (Exception $e) {
    // handle bad user input here
}

answered Nov 25, 2011 at 18:29

daiscog

12.2k8 gold badges55 silver badges63 bronze badges

1 Comment

sh03 Over a year ago

What about fetching all this instructions... "every clock cycle counts" brigade... ahah

Dharmendra Singh Patel · Accepted Answer · 2024-02-27 11:04:47Z

0

Sometimes API or other sources convert bool value (true, false) to string, you can check bool status by this code in PHP.

$boolFlag="false";

$convetToBool = json_decode($boolFlag);

if(!empty($convetToBool)){
  //do any work in true condtion;
}

answered Feb 27, 2024 at 11:04

Dharmendra Singh Patel

474 bronze badges

1 Comment

Eyad Bereh Over a year ago

Using json_decode() is too much overhead for a simple task as this, don't you think so ?

Ikhlak S. · Accepted Answer · 2018-06-11 08:56:59Z

-1

You can use is_bool to test your string:

if(is_bool($val)){
  // is boolean
}else{
  // not a boolean
}

answered Jun 11, 2018 at 8:56

Ikhlak S.

9,10411 gold badges60 silver badges80 bronze badges

1 Comment

Wesley Gonçalves Over a year ago

is_bool will return true only if $val is "pure" true or false, but it will return false for "true" and "false" strings.

Collectives™ on Stack Overflow

Test if string could be boolean PHP

9 Answers 9

5 Comments

6 Comments

Comments

Comments

Comments

Comments

1 Comment

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

9 Answers 9

5 Comments

6 Comments

Comments

Comments

Comments

Comments

1 Comment

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related