如何在php中使用字符串作为数学计算公式? [英] how to use a string as formula for mathematical calculations in php?

问题描述

mysql 行中存储了几个数学公式供个人使用.即一个字段包含此公式作为字符串 (varchar):(($a+$b)/$c)

There are several mathematical formulas stored in mysql rows for individual usage. i.e. a field contains this formula as a string (varchar): (($a+$b)/$c)

现在在 php 中变量由 foreach 循环动态填充:

Now in php variables are filled dynamically by an foreach loop:

$temp_array[$deviceData["devicename"]] = $deviceSum;

$deviceData["devicename"] 代表 $a、$b、$c.

该数组可以看起来像 $a=>20、$b=>30、$c=>580.

The array can look like $a=>20, $b=>30, $c=>580.

如何在字符串公式中使用这个变量?

感谢您的帮助.

推荐答案

很遗憾，您需要对其进行评估.

Unfortunately, you need to eval it.

如果值是这样的:

$deviceData["devicename"] = [
    'a' => 20,
    'b' => 30,
    'c' => 580
];

您可能想要隔离它们，因为如果有超过 3 个等，您需要 extract() 来使用它们，封装在函数/闭包中会起作用.

You might want to isolate them as you will need to extract() them out to make use if there is more then 3 etc, encapsulating in function/closure would work.

<?php
$formula = '(($a+$b)/$c)';

$deviceData["devicename"] = ['a' => 20, 'b' => 30, 'c' => 580];

$runFormula = function ($formula, $data) { 
    extract($data); 
    return eval('return '.$formula.';'); 
};

echo $runFormula($formula, $deviceData["devicename"]);

https://3v4l.org/I2rbk

或者只是:

extract($deviceData["devicename"]); 
echo eval('return '.$formula.';'); 

但是您正在使用提取的内容污染全局变量表，可能会导致更多问题.

But you're polluting your global variable table with whats extracted, potentially causing more issues.

虽然如果公式是由用户定义的，请不要使用 eval，否则您会遇到安全问题.

Though dont use eval if the formula is defined by the user, or your will have security issues.

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