I have a large mathematical expression that has to be created dynamically. For example, once I have parsed "something" the result will be a string like: "$foo+$bar/$baz";
.
So, for calculating the result of that expression I'm using the eval
function... something like this:
eval("\$result = $expresion;");
echo "The result is: $result";
The problem here is that sometimes I get errors that says there was a division by zero, and I don't know how to catch that Exception. I have tried things like:
eval("try{\$result = $expresion;}catch(Exception \$e){\$result = 0;}");
echo "The result is: $result";
Or:
try{
eval("\$result = $expresion;");
}
catch(Exception $e){
$result = 0;
}
echo "The result is: $result";
But it does not work. So, how can I avoid that my application crashes when there is a division by zero?
Edit:
First, I want to clarify something: the expression is built dynamically, so I can't just eval if the denominator is zero. So... with regards to the Mark Baker's comment, let me give you an example. My parser could build something like this:
"$foo + $bar * ( $baz / ( $foz - $bak ) )"
The parser build the string step by step without worrying about the value of the vars... so in this case if $foz == $bak
there's in fact a division by zero: $baz / ( 0 )
.
On the other hand as Pete suggested, I tried:
<?php
$a = 5;
$b = 0;
if(@eval(" try{ \$res = $a/$b; } catch(Exception \$e){}") === FALSE)
$res = 0;
echo "$res\n";
?>
But it does not print anything.
$expression
is dividing by zero beforehand? – Anthony Forloneyeval
can be a bad idea. You're now going to let your end-user execute PHP code on your server. I don't know an alternative, so I'm not posting an answer, but you should think about whether you want me to be able to type in any PHP code no matter how destructive into your webpage. – Umang