How to calculate strings with PHP
Ever wondering to calculate 2 + 2 ? Sure you have.
But what if your formula comes in a string input ?
So, how to calculate “2 + 2″ or “4 * ( 3 – 5 )” in PHP ?
We’ll have the function calculate_string($mathstring).
function calculate_string( $mathString ) {
$mathString = trim($mathString); // trim white spaces
$mathString = ereg_replace ('[^0-9\+-\*\/\(\) ]', '', $mathString); // remove any non-numbers chars; exception for math operators
$compute = create_function("", "return (" . $mathString . ");" );
return 0 + $compute();
}
$string = " (1 + 1) * (2 + 2)";
echo calculate_string($string); // outputs 8
Demo:
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thank you so much, after an hour searching, finally I found this website, calculate formula without eval(), look great. I’ll use your code in my final project.
A very nice trick. Took me a couple of seconds to realize what exactly you are doing but in fact its a very simple yet effective and most importantly eval-less aproach
Thanks for the idea. I will steal it
Thank you so much, i was very blank before i got this great solution from you.
very good!
thank u!
I dont know but I think that solution is same like eval …
Great..
Thanks
[...] This function is for calculating a given calculation in a string. e.g. (1+1)*(2+2) ‘Borrowed’ from http://www.website55.com/php-mysql/2010/04/how-to-calculate-strings-with-php.html [...]
I agree, there is no difference to using eval. You should no longer use “ereg_replace”, this is discontinued.
It shows me this error
Parse error: syntax error, unexpected ‘<' in /var/local/… : runtime-created function on line 1
on the line that calls create_function.
Could you tell me what can cause that?
$mathString='4+2'
The whole thing breaks as soon as the string doesn’t have the right syntax (eg. 3*(2+2)- ). And as it is the same as eval it’s quiet dangerous.
And ereg is indeed deprecated. But this shouldn’t be a big issue.