在vb.net中进行数学运算，例如javascript中的Eval [英] Doing math in vb.net like Eval in javascript

问题描述

有什么方法可以解析vb.net中的字符串(例如，内置方法)，可以像Eval一样进行数学运算吗?例如，3+(7/3.5)作为字符串将返回2.

Is there any way to parse a string in vb.net (like, built in methods), that can do math like Eval can? For example, 3+(7/3.5) as a string would return 2.

我不是要您为我编写代码，我只是想知道是否有内置方式来执行此操作，如果没有，我会自己编写.

I am not asking for you to code this for me, I just want to know if there is a built in way to do this, if there is not I will code it myself.

我敢打赌它将无法自行解析诸如Sin(90)之类的东西，而且我知道需要将其替换为Math.Sin(90).

I can wager that it would not be able to parse stuff like Sin(90) on its own, and I understand that would need to be replaced by Math.Sin(90).

如果有内置方法，您将如何使用它?

If there is a built in method, how do you use it?

推荐答案

使用

There's a shortcut for limited (ie. simple) math expressions by using the DataTable.Compute method. Obviously, this isn't robust (limited functionality) and feels hackish to misuse the DataTable for this purpose, but I figured I would add to the current answers.

示例:

var result = new DataTable().Compute("3+(7/3.5)", null); // 5

"Sin(90)"不适用于此方法.请参考 DataColumn.Expression属性页有关受支持功能的列表，特别是在聚合"部分下.

"Sin(90)" wouldn't work with this approach. Refer to the DataColumn.Expression Property page for a list of supported functions, specifically under the "Aggregates" section.

使用System.CodeDom命名空间是一种选择.

Using the System.CodeDom namespace is an option.

一些有用的链接:

• CodeDom计算器
• 使用CodeDom评估数学表达式
• 相关的SO问题: .NET中是否存在字符串数学评估器?

• CodeDom Calculator
• Evaluating mathematical expressions using CodeDom
• Related SO question: Is there a string math evaluator in .NET?

以解决您的评论，这是一种演示用等效的Math类方法替换三角函数的方法.

to address your comment, here is an approach to demonstrate replacing trigonometric functions with their equivalent Math class methods.

C#

string expression = "(Sin(0) + Cos(0)+Tan(0)) * 10";
string updatedExpression = Regex.Replace(expression, @"(?<func>Sin|Cos|Tan)\((?<arg>.*?)\)", match =>
            match.Groups["func"].Value == "Sin" ? Math.Sin(Int32.Parse(match.Groups["arg"].Value)).ToString() :
            match.Groups["func"].Value == "Cos" ? Math.Cos(Int32.Parse(match.Groups["arg"].Value)).ToString() :
            Math.Tan(Int32.Parse(match.Groups["arg"].Value)).ToString()
        );
var result = new DataTable().Compute(updatedExpression, null); // 10

VB.NET

Dim expression As String = "(Sin(0) + Cos(0)+Tan(0)) * 10"
Dim updatedExpression As String = Regex.Replace(expression, "(?<func>Sin|Cos|Tan)\((?<arg>.*?)\)", Function(match As Match) _
        If(match.Groups("func").Value = "Sin", Math.Sin(Int32.Parse(match.Groups("arg").Value)).ToString(), _
        If(match.Groups("func").Value = "Cos", Math.Cos(Int32.Parse(match.Groups("arg").Value)).ToString(), _
        Math.Tan(Int32.Parse(match.Groups("arg").Value)).ToString())) _
        )
Dim result = New DataTable().Compute(updatedExpression, Nothing)

但是，请注意，您需要了解"arg"组的内容.我知道它们是整数，因此我在它们上使用了Int32.Parse.如果它们是项目的组合，那么这种简单的方法将行不通.我怀疑如果由于无法支持更多函数调用而使解决方案变得过于复杂，那么您将经常需要对这些解决方案进行创可贴.在这种情况下，使用CodeDom方法或其他方法可能更合适.

Note, however, that you need to know the contents of the "arg" group. I know they are ints, so I used Int32.Parse on them. If they are a combination of items then this simple approach won't work. I suspect you will constantly need to band-aid the solution if it gets too complicated with more unsupported function calls, in which case the CodeDom approach or others may be more suitable.

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