php 比较浮点数 - 相同的数字，但不等于？
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Comparing floats - same number, but does not equal?
提问by jeffkee
Possible Duplicate:
How should I do floating point comparison?
php integer and float comparison mismatch
I have two variables, $_REQUEST['amount']and $carttotal, on an e-commerce thing. They of course should match when attempting to process a payment, so as to prevent a manual override of the payment amount at the last minute, or of course, a calculation error.
在电子商务方面，我有两个变量$_REQUEST['amount']和$carttotal。在尝试处理付款时，它们当然应该匹配，以防止在最后一分钟手动覆盖付款金额，或者当然，计算错误。
However:
然而：
$carttotal = $carttotal * 1;
$_REQUEST['amount'] = $_REQUEST['amount'] * 1;
if($carttotal != $_REQUEST['amount']) {
$code = 0; // cart empty under this user - cannot process payment!!!
$message = 'The cart total of ' . $carttotal . ' does not match ' . $_REQUEST['amount'] . '. Cannot process payment.';
$amount = $carttotal;
$json = array('code' => $code,
'message' => $message,
'amount' => $amount);
die(json_encode($json));
} else {
$trnOrderNumber = $client->id . '-' . $carttotal;
}
The above code, with the same numbers passed, is NOT giving me the equal. Basically I get the error message as if the $carttotal != $_REQUEST['amount']is true(unequal vars).
上面的代码，通过相同的数字，并没有给我相等的。基本上我得到的错误信息就好像$carttotal != $_REQUEST['amount']是true（不等的变量）。
So to test the vars, I snuck in:
所以为了测试变量，我偷偷地进来：
var_dump($_REQUEST['amount']);
var_dump($carttotal);
To see what is going on (after I do the * 1calculations to make sure they are dealt with as floats, not strings).
看看发生了什么（在我进行* 1计算以确保它们被处理为浮点数，而不是字符串之后）。
I got this back:
我得到了这个：
float(168.57)
float(168.57)
Very very frustrating. What could be causing this?
非常非常令人沮丧。什么可能导致这种情况？
采纳答案by dqhendricks
floating point numbers have limited precision. view the warning about comparing them here:
浮点数的精度有限。在此处查看有关比较它们的警告：
回答by Oliver A.
Floating point numbers are NOT 100% accurate! You calculation in PHP may return 10.00000000001 which is NOT equal to 10.
浮点数不是 100% 准确的！您在 PHP 中的计算可能会返回 10.00000000001，它不等于 10。
Use sprintf ( http://php.net/manual/en/function.sprintf.php) to format the floats before you compare them.
在比较浮点数之前，使用 sprintf ( http://php.net/manual/en/function.sprintf.php) 格式化浮点数。
回答by AR.
Instead of multiplying by one use number_format.
使用 number_format 代替乘以 1。
$carttotal = number_format((int)$carttotal,2,'.','');
$_REQUEST['amount'] = number_format((int)$_REQUEST['amount'],2,'.','');
