Parsing a string into a boolean value in PHP

There is a native PHP method of doing this which uses PHP's filter_var method:

$bool = filter_var($value, FILTER_VALIDATE_BOOLEAN);

According to PHP's manual:

Returns TRUE for "1", "true", "on" and "yes". Returns FALSE otherwise.

If FILTER_NULL_ON_FAILURE is set, FALSE is returned only for "0", "false", "off", "no", and "", and NULL is returned for all non-boolean values.

The reason is that all strings evaluate to true when converting them to boolean, except "0" and "" (empty string).

The following function will do exactly what you want: it behaves exactly like PHP, but will also evaluates the string "false" as false:

function isBoolean($value) {   if ($value && strtolower($value) !== "false") {      return true;   } else {      return false;   }}

The documentation explains that: http://php.net/manual/en/language.types.boolean.php :

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
• the special type NULL (including unset variables)
• SimpleXML objects created from empty tags

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

In PHP only "0" or the empty string coerce to false; every other non-empty string coerces to true. From the manual:

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

• the empty string, and the string "0"

You need to write your own function to handle the strings "true" vs "false". Here, I assume everything else defaults to false:

function isBoolean($value) {   if ($value === "true") {      return true;   } else {      return false;   }}

On a side note that could easily be condensed to

function isBoolean($value) {   return $value === "true";}