Strange error in PHP | number zero (0) evaluates to true against a string in PHP
Published by Nicholas Dunbar on March 27th, 2013
Reproducing the error (see solution below):
Take a look at this weird error below:
$int_zero="reset";
$str_zero="0";
$int_zero=intval($str_zero);
if ($int_zero == "reset"){
$str_zero="0";
$int_zero=intval($str_zero);
if ($int_zero == "reset"){
echo "equals reset\n";
} else {
echo "equals something else\n";
}
echo $int_zero."\n";
Output:
equals reset
0
So strange n'est pas? This should not happen. At first, I thought it had to do with the intval or floatval functions since I tried both and got the same result. But it turns out this is wrong. For example I created a function that returns 0 without the use of intval when it is a zero.
Replace intval, still an error
function intval_v2($str){
$str = trim($str);
if (preg_match("/^(\s|0|\.)*$/",$str)){
return 0;
} else {
return intval($str);
}
}
$str = trim($str);
if (preg_match("/^(\s|0|\.)*$/",$str)){
return 0;
} else {
return intval($str);
}
}
When I use this function instead of intval, I still get the same bad result. In fact if I do the following I get the same result.
Don't use intval...still..bzzzz...wrong
$int_zero=0;
$some_num=3;
$some_num = $int_zero;
if ($some_num == "whatever it does not matter"){
echo "equals whatever it does not matter\n";
} else {
echo "equals a number\n";
}
echo "$some_num\n";
$some_num=3;
$some_num = $int_zero;
if ($some_num == "whatever it does not matter"){
echo "equals whatever it does not matter\n";
} else {
echo "equals a number\n";
}
echo "$some_num\n";
Output:
equals whatever it does not matter
0
0
The work around...
The way around it is to use a strict comparison known as the triple equal operator (===) the problem is the zero (0) not the intval or floatval functions.
$int_zero=0;
$some_num=3;
$some_num = $int_zero;
if ($some_num === "whatever it does not matter"){
echo "equals whatever it does not matter\n";
} else {
echo "equals a number\n";
}
echo "$some_num\n";
$some_num=3;
$some_num = $int_zero;
if ($some_num === "whatever it does not matter"){
echo "equals whatever it does not matter\n";
} else {
echo "equals a number\n";
}
echo "$some_num\n";
Output:
equals a number
0
PHP has lost major cool points from me this day.
Posted on March 27th, 2013