在php中处理数学方程式 [英] Process mathematical equations in php

问题描述

允许用户输入他们喜欢的任何数学方程式(带有一个变量):

A user is allowed to enter any mathematical equation they like (with one variable):

x + 5

1 - x/2

(x/3) * (56/13)

这些作为字符串存储在数据库中.检索它们后，我需要用'x'代替一个数字并检查方程式的值.

These are stored as strings in the database. When they are retrieved I need to substitute 'x' for a number and check the value of the equation.

我该怎么办?

我当时正在考虑编写一个解析器来解构字符串并将其转换为方程式，但这听起来很昂贵且存在问题.另一种选择是让它们通过eval(但是如果可以帮助的话，我不是使用eval的忠实粉丝).

I was considering writing a parser to deconstruct the strings and turn them into equations, however this sounds expensive and problematic. The other option is to pass them through eval (but I'm not a great fan of using eval if I can help it).

有什么想法吗?

更新: 我还需要能够获得类似(x> 5)"的布尔值.使用evalMath不可能

UPDATE: I also need to be able to get the boolean value of something like "(x > 5)". This is not possible with evalMath

更新2: 我需要一秒钟将它们发射出很多.我一直在研究php中的eval，但无法获取它返回(5> 4)的布尔值，但是我注意到js会这样做...也许我应该研究node.js ...

UPDATE 2: I need to fire lots of these a second. I've been looking into eval in php but cant get it to return a boolean for (5 > 4) however I noticed js would do it... maybe I should investigate node.js...

更新3: 在尝试了一下node.js(并使其正常工作)后，我回过头来，开始在PHP中进行评估，请参见:

UPDATE 3: After having some fun trying out node.js (and getting it to work) I went back and got eval to work in PHP see: Can php eval return a boolean value?

因此，我将在eval上使用对用户输入非常非常严格的过滤器.

So I will go with eval with a very very hardcore filter on user input.

推荐答案

Eval不是邪恶的！！！！！

Eval is not Evil!!!!!

是的，如果您编写错误的代码，它可能会完全塞满您的系统-但是最新的PHP版本可以解析无效的表达式而不会导致整个脚本崩溃.还有许多其他方法可以通过编写错误的代码来公开系统.

Yes it can stuff your system up completely if you write bad code - but recent PHP versions can parse an invalid expression without crashing the whole script. And there are many other ways of exposing your system by writing bad code.

这只剩下代码注入攻击的可能性-通过对不是安全字符的Everythnig进行preg_replace即可轻松避免(例如0 .... 9，(，)，+，-，*，/，^，.)

That just leaves the possiblity of code injection attacks - which can easily be avoided by doing a preg_replace on everythnig which is not a safe character (i.e. 0....9, (, ), +, -, *, /, ^, .)

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