php string to int not working

Question

I am trying to cut an image for small pieces from database. My code here:

$image = imagecreatefromjpeg($filename);
$width = $row['width'];
$height = $row['height'];
$new_width = 480;
$new_height = 360;          
$offset_x =  (int)(round($height*360/$width));//100
$offset_y = 0;
$new_image = imagecreatetruecolor($new_width, $new_height);
imagecopy($new_image, $image, 0, 0, $offset_x, $offset_y, $width, $height);
imagejpeg($new_image,$newimg);

But in the line $offset_x, the (int)(round($height*360/$width)) is not working. If I put an intval, like 100, all the images will cut well, but the offset position is not willing. So how to true string to int?

BTW: In this case, I will call and cut image from database in a foreach, should I unset something after this code in the foreach?

where is $row set? What are the values of $height and $width? — ben
– ben, Commented Dec 15, 2011 at 21:52
maybe try intval $offset_x = intval(round($height*360/$width)); php.net/manual/en/function.intval.php — rogerlsmith
– rogerlsmith, Commented Dec 15, 2011 at 21:55
@ben, $height, $width from mysql query => $row['width'] and $row['height']. — fish man
– fish man, Commented Dec 15, 2011 at 21:55
@fishman: Did you try casting $width and $height as ints? If they are ints then the result should also be an int. — Mike Purcell
– Mike Purcell, Commented Dec 15, 2011 at 21:58

Alex Turpin · Accepted Answer · 2011-12-15 21:57:28Z

3

You rarely need to convert strings to numbers in PHP, it does that implicitely pretty well. For example, your code works just fine without any added conversions:

<?php
    $height = '100';
    $width = '200';
    $offset = round($height * 360 / $width);
    echo $offset;
?>

http://codepad.viper-7.com/LJEXIF

The problem you might be having, if it's not giving you the right result, is the priority of operations. Your code,

round($height * 360 / $width)

Is the equivalent of

round($height * (360 / $width))

It will first divide 360 by $width, then multiply the result by $height. If that's what you wanted, then your problem lies elsewhere. You should try and reproduce your problem with test variables on http://codepad.viper-7.com and post it back here.

answered Dec 15, 2011 at 21:57

Alex Turpin

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3 Comments

aziz punjani Over a year ago

Initially i thought that division happens before multiplication but that's not the case according to the operator precedence chart php.net/manual/en/language.operators.precedence.php or am i not reading it right ?

Alex Turpin Over a year ago

@Interstellar_Coder it follows standard mathematics priority of operation, PEDMAS (Parenthesis Exponent Division Multiplication Addition Substraction), as you can see here codepad.viper-7.com/xOcjTQ. That chart is a ltitle misleading. The elements on top have precedence over the elements towards the bottom. The positioning of the elements within the "operator" column seems to be random.

aziz punjani Over a year ago

Ahh yes Xeon, i'm glad it follows PEDMAS, initially this is what i suspected but after looking at the chart i got super confused. The page says that within the operator column for that row the operators have precedence from left to right which i guess is wrong! Thanks for the clarification.

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