Evaluate C# Code (Eval Function)

kim.david.hauser

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12 Oct 2005CPOL

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An example that provides an Eval function for compiling/evaluating C# code at runtime.

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Introduction

This example shows an "Eval" function for C# and implements different usages of this evaluate function. The library is written in C# and can be tested with the MainForm in the solution.

Source view

Here you will see all the trick. The code generates a class structure with a basic "function prototype" in which the code to evaluate is filled in. The execution of the function should execute your code:

// Eval > Evaluates C# sourcelanguage
public static object Eval(string sCSCode) {

  CSharpCodeProvider c = new CSharpCodeProvider();
  ICodeCompiler icc = c.CreateCompiler();
  CompilerParameters cp = new CompilerParameters();

  cp.ReferencedAssemblies.Add("system.dll");
  cp.ReferencedAssemblies.Add("system.xml.dll");
  cp.ReferencedAssemblies.Add("system.data.dll");
  cp.ReferencedAssemblies.Add("system.windows.forms.dll");
  cp.ReferencedAssemblies.Add("system.drawing.dll");

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

  StringBuilder sb = new StringBuilder("");
  sb.Append("using System;\n" );
  sb.Append("using System.Xml;\n");
  sb.Append("using System.Data;\n");
  sb.Append("using System.Data.SqlClient;\n");
  sb.Append("using System.Windows.Forms;\n");
  sb.Append("using System.Drawing;\n");

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

  CompilerResults cr = icc.CompileAssemblyFromSource(cp, sb.ToString());
  if( cr.Errors.Count > 0 ){
      MessageBox.Show("ERROR: " + cr.Errors[0].ErrorText, 
         "Error evaluating cs code", MessageBoxButtons.OK, 
         MessageBoxIcon.Error );
      return null;
  }

  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;

}

Thanks fly out to:

Jérôme Poudo - Post @ GotDotNet.

Credits:

Kim Hauser (dave) - Application Developer & System Engineer.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

kim.david.hauser

Software Developer (Senior)

Switzerland

programmer and software junkie since 1991 zurich switzerland

Comments and Discussions

Re: Uses

kim.david.hauser2-Nov-05 11:03

kim.david.hauser

2-Nov-05 11:03

I'm a bit late, but what kind of expressions do you want to eavl? Are they really complicate or like 100 * 1000 / 20, because if you need variables and complex opperation, it would be a good thing to think about a little script language witch wrapps your math expression (inputed as one expression or via config (ie. hp style)) and then executes a genereted code over the eval function. If you just want to calculate some numbers you can write a text parser and do the calculation without eval.

IMPORTANT:
If you use this (thi 1st) source example (2nd is coming soon - sooon!!!), make sure to load the new assembly into an new AppDomain, else it will eat up all your memory

greez kim

Thanks for review...

kim.david.hauser21-Oct-05 10:13

kim.david.hauser

21-Oct-05 10:13

Thanks for all your response. Sorry for the long time it took to answere and the less documentation i'd supply with the example, but I'm working on a real interesting project at the moment and it's really time consuming, at least for me Smile | :)

. To this example and the code provided: this is just a mix of a vb.net example and some c# snippets i've found, and should show a basic meaning of dynamically compiling code in c# (it's a conversion from vb.net). - till then use the EvalCSCode.cs class and customize to your needs :->

I agree with some of you, that there should be more introducion to the problem it solves. I think I'll update this topic soon with an new example and text. thanx again for review and keep on coding & posting - regards dave

Using a static method instead

19-Oct-05 20:07

It's great, but... why don't you use a static method? I think it would be faster than a new instance. Confused | :confused:

Re: Using a static method instead

aprenot21-Oct-05 10:17

aprenot

21-Oct-05 10:17

looks static to me:

public static object Eval(string sCSCode)

Re: Using a static method instead

Toli Cuturicu20-Dec-10 11:22

Toli Cuturicu

20-Dec-10 11:22

No... He meant the stub class and its method should be static. Those created on the fly.

Excellent! But

cccccbbbbb19-Oct-05 14:41

cccccbbbbb

19-Oct-05 14:41

It's Excellent, but every time when the func is called, a temp assembly will be created and loaded into the application, these assemblies will stay there until current appdomain unload. The more the func is callled, the more temp assemblies will be loaded. So, if current appdomain is the default appdomain of the application then ...

Re: Excellent! But

kim.david.hauser22-Oct-05 0:29

kim.david.hauser

22-Oct-05 0:29

Your right - thats a good point. Im working on that - try loading all of the evaled code (the new compiled assembly) into a new AppDomain - see:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dncscol/html/csharp05162002.asp[^]

any corrections or other examples are appreciated Roll eyes | :rolleyes:

Re: Excellent! But

Kevan Davis1-Dec-06 11:18

Kevan Davis

1-Dec-06 11:18

Used this is a project I'm working on. It's a slight modification of what you posted.
I also tried to figure out the AppDomain, this is where I got when I ran into a brick wall.
In order to load the code into the new AppDomain, you will need 2 classes, the first class creates the AppDomain, and loads the 2nd class into it, similar to what I have at the bottom. The second class will inherit MarshalByRefObject and will do all the dynamic compilation.
When/if I get around to finishing this, I'll post it as well.

<br />
using System;<br />
using System.CodeDom.Compiler;<br />
using System.Collections.Generic;<br />
using System.Text;<br />
using System.Windows.Forms;<br />
using Microsoft.CSharp;<br />
<br />
namespace Test<br />
{<br />
    /// <summary><br />
    /// C# Code Evaluator<br />
    /// Based on work by Kim Hauser found at http://www.codeproject.com/csharp/evalcscode.asp<br />
    /// </summary><br />
    class CSEvaluator<br />
    {<br />
        /// <summary><br />
        /// Assemblies are what follow "using"<br />
        /// </summary><br />
        public List<string> Assemblies;<br />
        /// <summary><br />
        /// References are in the Solution Explorer in the References folder<br />
        /// </summary><br />
        public List<string> References;<br />
        /// <summary><br />
        /// Namespace to evaluate in, in case you want to be able to access external classes<br />
        /// </summary><br />
        public string Namespace;<br />
<br />
        public CSEvaluator()<br />
        {<br />
            References = new List<string>();<br />
            // Adding default References<br />
            References.Add("System");<br />
            References.Add("System.Drawing");<br />
            References.Add("System.Windows.Forms");<br />
            References.Add("System.Xml");<br />
<br />
            Assemblies = new List<string>();<br />
            // Adding default assemblies<br />
            Assemblies.Add("System");<br />
            Assemblies.Add("System.Drawing");<br />
            Assemblies.Add("System.Drawing.Drawing2D"); // notice that Drawing2D is not in the list of references<br />
            Assemblies.Add("System.Windows.Forms");     //    this is because System.Drawing is the reference for it<br />
            Assemblies.Add("System.Xml");<br />
<br />
            Namespace = this.GetType().Namespace.ToString();<br />
        }<br />
<br />
        /// <summary><br />
        /// Evaluates C# Code<br />
        /// </summary><br />
        /// <param name="sCSCode">The Code to evaluate</param><br />
        /// <param name="sParms">parameter string, i.e. "string sCSCode, string sParms, object[] oParms"</param><br />
        /// <param name="oParms">array of parameter objects</param><br />
        /// <returns></returns><br />
        public object Eval(string sCSCode, string sParms, object[] oParms)<br />
        {<br />
            CompilerParameters cp = new CompilerParameters();<br />
<br />
            // load references<br />
            foreach (string r in References)<br />
                cp.ReferencedAssemblies.Add(r + ".dll");<br />
<br />
            cp.CompilerOptions = "/t:library";<br />
            cp.GenerateInMemory = true;<br />
<br />
            StringBuilder sb = new StringBuilder("");<br />
            // load assemblies<br />
            foreach (string s in Assemblies)<br />
                sb.Append("using " + s + ";\n");<br />
<br />
            sb.Append("\nnamespace " + Namespace + "\n{\n");<br />
            sb.Append("\tpublic class temp_Eval\n\t{\n");<br />
            sb.Append("\t\tpublic object Eval(" + sParms + ")\n\t\t{\n");<br />
            sb.Append("\t\t\treturn " + sCSCode + "; \n");<br />
            sb.Append("\t\t}\n");<br />
            sb.Append("\t}\n");<br />
            sb.Append("}\n");<br />
<br />
            CompilerResults cr = CodeDomProvider.CreateProvider("CSharp").CompileAssemblyFromSource(cp, sb.ToString());<br />
            if (cr.Errors.Count > 0)<br />
            {<br />
                MessageBox.Show("ERROR: " + cr.Errors[0].ErrorText,<br />
                   "Error evaluating cs code", MessageBoxButtons.OK,<br />
                   MessageBoxIcon.Error);<br />
                return null;<br />
            }<br />
<br />
            // *** Below this point is a work in progress, watch out for falling debris ***<br />
<br />
            //AppDomain evalDomain = AppDomain.CreateDomain("evalDomain");<br />
            System.Reflection.Assembly a = cr.CompiledAssembly;<br />
            //evalDomain.DefineDynamicAssembly(a.GetName(), System.Reflection.Emit.AssemblyBuilderAccess.Run); // problem here can be solved with MarshalByRefObject<br />
            //object o = evalDomain.CreateInstance(a.GetName().ToString(), Namespace + ".temp_Eval"); // it probably won't work like this<br />
            object o = a.CreateInstance(Namespace + ".temp_Eval");<br />
<br />
            Type t = o.GetType();<br />
            System.Reflection.MethodInfo mi = t.GetMethod("Eval");<br />
<br />
            object ec = mi.Invoke(o, oParms);<br />
<br />
            //AppDomain.Unload(evalDomain);<br />
            return ec;<br />
        }<br />
    }<br />
}<br />

Excellent !!

Tittle Joseph18-Oct-05 19:46

Tittle Joseph

18-Oct-05 19:46

I havent downloaded it so far to see it working. But I really appreciate your work in advance.

I've been working on javascript for a quite long time and admire its "eval" function, and I was missing it in C#. You have really done great job having same in C#. I'll bookmark this page because I know I'll need it one day.

And as some1 said above; not every1 knows how powerful this function is.

---------
Tittle

Thanks, but ...

Herman Chelette18-Oct-05 2:33

Herman Chelette

18-Oct-05 2:33

This is certainly an elegant, and beautifuly simple, solution! Thank you for sharing it. However, it would be nice for most of us out here reading it if there were a bit more discussion up front about the problem that it solves. I suspect that it will not be utilized as much as it could be (or rated as high, for that matter!) because many won't realize how powerful it is.

Anyway, thanks again for giving it to us - it surely gets my "5".

Herman Chelette
"Damn the specs! Find the elegant solution!!"

Re: Thanks, but ...

kim.david.hauser21-Oct-05 9:34

kim.david.hauser

21-Oct-05 9:34

Thanks for your comment, i think about a update of this topic in the near future. Due to my permanent lack of time Smile | :)

i didn't post realy much - sorry for that.

Great Job

aprenot13-Oct-05 5:02

aprenot

13-Oct-05 5:02

Good article. I am curious as to whether or not you could get a list of all assemblies already in memory and reference them. That way, if a user has an eval statement against custom objects, it would still work.

Re: Great Job

Anonymous21-Oct-05 9:52

Anonymous

21-Oct-05 9:52

try using this:

using System.Reflection;

Assembly[] loadedAssemblies = AppDomain.CurrentDomain.GetAssemblies();
foreach( Assembly assembly in loadedAssemblies ){
try{
Console.WriteLine(assembly.FullName);
}catch( TypeLoadException tlexec ){}

regards dave

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