CODEWITHSUNDEEP
c#reflectioneval
Daren Thomas
Daren Thomas

Reputation: 70314

How can I evaluate a C# expression dynamically?

I would like to do the equivalent of:

object result = Eval("1 + 3");
string now    = Eval("System.DateTime.Now().ToString()") as string

Following Biri s link, I got this snippet (modified to remove obsolete method ICodeCompiler.CreateCompiler():

private object Eval(string sExpression)
{
    CSharpCodeProvider c = new CSharpCodeProvider();
    CompilerParameters cp = new CompilerParameters();

    cp.ReferencedAssemblies.Add("system.dll");

    cp.CompilerOptions = "/t:library";
    cp.GenerateInMemory = true;

    StringBuilder sb = new StringBuilder("");
    sb.Append("using System;\n");

    sb.Append("namespace CSCodeEvaler{ \n");
    sb.Append("public class CSCodeEvaler{ \n");
    sb.Append("public object EvalCode(){\n");
    sb.Append("return " + sExpression + "; \n");
    sb.Append("} \n");
    sb.Append("} \n");
    sb.Append("}\n");

    CompilerResults cr = c.CompileAssemblyFromSource(cp, sb.ToString());
    if (cr.Errors.Count > 0)
    {
        throw new InvalidExpressionException(
            string.Format("Error ({0}) evaluating: {1}", 
            cr.Errors[0].ErrorText, sExpression));
    }

    System.Reflection.Assembly a = cr.CompiledAssembly;
    object o = a.CreateInstance("CSCodeEvaler.CSCodeEvaler");

    Type t = o.GetType();
    MethodInfo mi = t.GetMethod("EvalCode");

    object s = mi.Invoke(o, null);
    return s;

}

Upvotes: 65

Views: 135342

Answers (11)

Hakkı ÜN
Hakkı ÜN

Reputation: 1

    static double EvaluateExpression(string expression)
    {
        DataTable table = new DataTable();
        table.Columns.Add("expression", typeof(string), expression);
        DataRow row = table.NewRow();
        table.Rows.Add(row);
        return double.Parse((string)row["expression"]);
    }

MessageBox.Show( EvaluateExpression("((15.3 * 0.15) / 100 ) * 0.005 + (8500 * 0.754878)").ToString() );

Result : 6416.46311475

Upvotes: 0

Phillip Rochester
Phillip Rochester

Reputation: 87

Just pass your aritmetic expression to sql using a conection string

// INPUT
string eval = "SELECT ((1+2)-3*4)/5.0";

string strCon = $"Server=.\sqlexpress; Database=master; integrated security = true";

SqlConnection sqlCon = new SqlConnection(strCon);
sqlCon.Open();

SqlCommand cmd = new SqlCommand(eval, sqlCon);

SqlDataAdapter da = new SqlDataAdapter(cmd);
string result = da.SelectCommand.ExecuteScalar().ToString();

// OUTPUT
Console.WriteLine(result);

You must add using System.Data.SqlClient;

Upvotes: 0

Ridkuma
Ridkuma

Reputation: 626

Old topic, but considering this is one of the first threads showing up when googling, here is an updated solution.

You can use Roslyn's new Scripting API to evaluate expressions.

If you are using NuGet, just add a dependency to Microsoft.CodeAnalysis.CSharp.Scripting. To evaluate the examples you provided, it is as simple as:

var result = CSharpScript.EvaluateAsync("1 + 3").Result;

This obviously does not make use of the scripting engine's async capabilities.

You can also specify the evaluated result type as you intended:

var now = CSharpScript.EvaluateAsync<string>("System.DateTime.Now.ToString()").Result;

To evaluate more advanced code snippets, pass parameters, provide references, namespaces and whatnot, check the wiki linked above.

Upvotes: 51

Venugopal M
Venugopal M

Reputation: 2412

There is a nice piece of code here https://www.c-sharpcorner.com/article/codedom-calculator-evaluating-c-sharp-math-expressions-dynamica/

Download this and make it a class library which may be referenced in your project. This seems to be pretty fast and simple

Perhaps this could help !

Upvotes: 0

Binh
Binh

Reputation: 291

I have just written a similar library (Matheval) in pure C#. It allows evaluating string and number expression like excel fomular.

using System;
using org.matheval;
                    
public class Program
{
    public static void Main()
    {
        Expression expression = new Expression("IF(time>8, (HOUR_SALARY*8) + (HOUR_SALARY*1.25*(time-8)), HOUR_SALARY*time)");
        //bind variable
        expression.Bind("HOUR_SALARY", 10);
        expression.Bind("time", 9);
        //eval
        Decimal salary = expression.Eval<Decimal>();    
        Console.WriteLine(salary);
    }
}

Upvotes: 2

cdiggins
cdiggins

Reputation: 18203

If you specifically want to call into code and assemblies in your own project I would advocate using the C# CodeDom CodeProvider.

Here is a list of the most popular approaches that I am aware of for evaluating string expressions dynamically in C#.

Microsoft Solutions

Non-Microsoft solutions (not that there is anything wrong with that)

Upvotes: 26

JJJ
JJJ

Reputation: 569

What are the performance implications of doing this?

We use a system based on something like the above mentioned, where each C# script is compiled to an in-memory assembly and executed in a separate AppDomain. There's no caching system yet, so the scripts are recompiled every time they run. I've done some simple testing and a very simple "Hello World" script compiles in about 0.7 seconds on my machine, including loading the script from disk. 0.7 seconds is fine for a scripting system, but might be too slow for responding to user input, in that case a dedicated parser/compiler like Flee might be better.

using System;
public class Test
{
    static public void DoStuff( Scripting.IJob Job)
    {
        Console.WriteLine( "Heps" );
    }
}

Upvotes: 1

Davide Icardi
Davide Icardi

Reputation: 12209

I have written an open source project, Dynamic Expresso, that can convert text expression written using a C# syntax into delegates (or expression tree). Text expressions are parsed and transformed into Expression Trees without using compilation or reflection.

You can write something like:

var interpreter = new Interpreter();
var result = interpreter.Eval("8 / 2 + 2");

or

var interpreter = new Interpreter()
                .SetVariable("service", new ServiceExample());

string expression = "x > 4 ? service.aMethod() : service.AnotherMethod()";

Lambda parsedExpression = interpreter.Parse(expression, 
                        new Parameter("x", typeof(int)));

parsedExpression.Invoke(5);

My work is based on Scott Gu article http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx .

Upvotes: 33

xnaterm
xnaterm

Reputation: 47

While C# doesn't have any support for an Eval method natively, I have a C# eval program that does allow for evaluating C# code. It provides for evaluating C# code at runtime and supports many C# statements. In fact, this code is usable within any .NET project, however, it is limited to using C# syntax. Have a look at my website, http://csharp-eval.com, for additional details.

Upvotes: 0

Rudolf_Abel
Rudolf_Abel

Reputation: 21

using System;
using Microsoft.JScript;
using Microsoft.JScript.Vsa;
using Convert = Microsoft.JScript.Convert;

namespace System
{
    public class MathEvaluator : INeedEngine
    {
        private VsaEngine vsaEngine;

        public virtual String Evaluate(string expr)
        {
            var engine = (INeedEngine)this;
            var result = Eval.JScriptEvaluate(expr, engine.GetEngine());

            return Convert.ToString(result, true);
        }

        VsaEngine INeedEngine.GetEngine()
        {
            vsaEngine = vsaEngine ?? VsaEngine.CreateEngineWithType(this.GetType().TypeHandle);
            return vsaEngine;
        }

        void INeedEngine.SetEngine(VsaEngine engine)
        {
            vsaEngine = engine;
        }
    }
}

Upvotes: 2

Reputation:

Looks like there is also a way of doing it using RegEx and XPathNavigator to evaluate the expression. I did not have the chance to test it yet but I kind of liked it because it did not require to compile code at runtime or use libraries that could not be available.

http://www.webtips.co.in/c/evaluate-function-in-c-net-as-eval-function-in-javascript.aspx

I'll try it and tell later if it worked. I also intend to try it in Silverlight, but it is too late and I'm almost asleep to do it now.

Upvotes: 0

Related Questions