if else strangeness

txupo

I have the most basic of problems. I was able to resolve it but it bugs me. I am trying to make sure that booleans are always reduced to 0 or 1 for the purposes of storage in mysql.

if ( ($bool === false || $bool === "false" || $bool == "false" || $bool == 0))
$bool = 0;
else
$bool = 1;

if "true" gets passed as a string $bool is assigned to 0. I don't get that. Below is the fix that I made. But it doesn't make any sense to me why I need it. I am relatively new to PHP but I keep getting hung up on little things like this.

if( ($bool === false || $bool === "false" || $bool == "false" || $bool == 0) && $bool != "true" )
$bool = 0;
else
$bool = 1;

I really want to know why the one at the top fails.

Thanks for looking at this.

Robert

weekender

not sure why "true" equates to boolean FALSE - it must be something to do with php's automatic type casting

but you don't need to do these if statements - in fact, it is impossible for them to have any effect, as 0 === FALSE === off etc etc

ie when you set $bool = 0, you are also setting $bool = FALSE and $bool = off

adam

txupo

...by another programmer that I have worked with that if you don't ensure that all bool are exactly 0 or 1 you will have problems with mysql. In other words "false" will not evaluate to 0 in the database.

I checked the documentation for mysql and as of 4.1 mysql will recognize TRUE or true and FALSE or false. Unfortuneatly, I am using 4.0.13.

Thanks for mentioning type casting. That must be it.

Robert

laserlight

The string "true" should have a boolean value of true, or a numeric value of 0.

The reason for the boolean value of true is:

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
the special type NULL (including unset variables)
Every other value is considered TRUE (including any resource).

The reason for the numeric value of 0 is:

The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero).

($bool === false || $bool === "false" || $bool == "false" || $bool == 0)

Now, none of the first 3 comparisons satisfy $bool having a boolean true value.
But the last comparison loosely compares with 0.
Since "true" can be typecasted to 0, this comparison returns true.
Hence the whole conditional is true, so $bool is set to 0.