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Posted 6 Mar 2006

C# Eval Function

, 21 Jun 2007
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C# eval function


This article is about a C# eval function, how to parse an expression and evaluate it. It supports Boolean, Bitwise, Arithmetic, Unary, Paren, Member (such as, Indexer (such as array[index]) and ConditionalIf(?:), it also supports Variable assign.

You can use it to evaluate one statement in the C# source code.

It does not use runtime compiler.

It does not use JScript.NET.

It does not use DataTable.

Using the Code

Expression Example



All functions or properties use Reflection to eval. It has no global function and its syntax is checked at runtime.
If you let Parameter 'string'=typeof(string), then it can do like this:


If a parameter is a type, it will call its static function or property.





Sample Use

using System;
using Jyc.Expr;
namespace TestExpr
    class Program
        static void Main(string[] args)
            Parser ep = new Parser();
            Evaluater evaluater = new Evaluater();
            ParameterVariableHolder pvh = new ParameterVariableHolder();

            pvh.Parameters["char"] = new Parameter(typeof(char));
            pvh.Parameters["sbyte"] = new Parameter(typeof(sbyte));
            pvh.Parameters["byte"] = new Parameter(typeof(byte));
            pvh.Parameters["short"] = new Parameter(typeof(short));
            pvh.Parameters["ushort"] = new Parameter(typeof(ushort));
            pvh.Parameters["int"] = new Parameter(typeof(int));
            pvh.Parameters["uint"] = new Parameter(typeof(uint));
            pvh.Parameters["long"] = new Parameter(typeof(string));
            pvh.Parameters["ulong"] = new Parameter(typeof(ulong));
            pvh.Parameters["float"] = new Parameter(typeof(float));
            pvh.Parameters["double"] = new Parameter(typeof(double));
            pvh.Parameters["decimal"] = new Parameter(typeof(decimal));
            pvh.Parameters["DateTime"] = new Parameter(typeof(DateTime));
            pvh.Parameters["string"] = new Parameter(typeof(string));

            pvh.Parameters["Guid"] = new Parameter(typeof(Guid));

            pvh.Parameters["Convert"] = new Parameter(typeof(Convert));
            pvh.Parameters["Math"] = new Parameter(typeof(Math));
            pvh.Parameters["Array "] = new Parameter(typeof(Array));
            pvh.Parameters["Random"] = new Parameter(typeof(Random));
            pvh.Parameters["TimeZone"] = new Parameter(typeof(TimeZone));
            pvh.Parameters["AppDomain "] = new Parameter(typeof(AppDomain));

            pvh.Parameters["Console"] = new Parameter(typeof(Console));

            pvh.Parameters["evaluater"] = new Parameter(evaluater);

            evaluater.VariableHolder = pvh;

            while (true)
                System.Console.WriteLine("Input line,press Return to Eval:");
                string line = System.Console.ReadLine().Trim();
                if (string.IsNullOrEmpty(line))
                    Tree tree = ep.Parse(line);


                    object result = evaluater.Eval(tree);

                    if( result != null )
                        System.Console.WriteLine("Result:{0}", result);
                        System.Console.WriteLine("Result is null");
                catch (Exception e)
                    System.Console.WriteLine("Exception:" + e.GetType().Name _
                                               +"->"+ e.Message);


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


About the Author

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QuestionBug in Scanner.cs, at line 453 Pin
Member 864646714-Feb-12 8:42
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QuestionThanks Pin
bildik9-Aug-11 11:58
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GeneralMy vote of 5 Pin
ChenNoam4-Oct-10 22:17
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GeneralGracias! Pin
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Generalthanks! Pin
bpbrainiak4-May-10 5:00
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GeneralRounding problem Pin
Pauline Cole30-Nov-09 12:20
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GeneralCalculation bug with negative numbers Pin
Pauline Cole12-Oct-09 0:51
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GeneralRe: Calculation bug with negative numbers Pin
bpbrainiak4-May-10 4:56
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KeitaroSan8-Oct-09 8:17
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GeneralDon't use it for work, only for learning stuff Pin
Dannie Juge30-Sep-09 4:25
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QuestionParse as decimal values Pin
palswim15-Jun-09 12:35
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AnswerRe: Parse as decimal values Pin
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GeneralLicense Pin
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GeneralRe: License Pin
devilplusplus30-May-09 16:30
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GeneralOne slight correction in the test code Pin
Andrew Kaiser26-Nov-08 3:26
memberAndrew Kaiser26-Nov-08 3:26 
GeneralCalculation Error Pin
pauf15-Nov-08 1:42
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QuestionAssign Variables Pin
j_jpg12-Nov-08 1:54
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GeneralGreat work Pin
ChenNoam5-Nov-08 23:44
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Generalcan't parse Pin
jameswei1-Oct-08 17:43
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AnswerRe: can't parse Pin
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Questionis it possible to add variable in runtime ? Pin
naamakat25-May-08 3:15
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AnswerRe: is it possible to add variable in runtime ? Pin
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GeneralGetting data from a deep object Pin
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QuestionLicense Pin
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GeneralRe: License Pin
devilplusplus8-Apr-08 15:09
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NewsScript.NET Pin
Extrim18-Oct-07 7:09
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General.Net 1 version Pin
shaluka20-Jun-07 6:50
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GeneralRe: .Net 1 version Pin
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GeneralRe: .Net 1 version Pin
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devilplusplus5-Jul-07 17:55
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QuestionRe: .Net 1 version Pin
shaluka6-Jul-07 0:31
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QuestionIs this a bug? Pin
shaluka22-May-07 0:01
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AnswerRe: Is this a bug? Pin
devilplusplus30-May-07 17:04
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QuestionEscape inverted commas [modified] Pin
shaluka9-May-07 0:58
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AnswerRe: Escape inverted commas Pin
devilplusplus30-May-07 17:05
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GeneralSpelling Pin
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GeneralRe: Spelling Pin
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Herbert Sauro27-Apr-07 15:11
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GeneralProblem when evaluate a correct expression after evaluate an invalid expression Pin
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GeneralProblem with strings Pin
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AnswerRe: Problem with strings Pin
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GeneralRe: Problem with strings Pin
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GeneralRe: Problem with strings Pin
Coyotelapa26-Apr-07 2:36
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GeneralProblem using boolean operators Pin
shaluka24-Apr-07 2:21
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GeneralRe: Problem using boolean operators Pin
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GeneralRe: Problem using boolean operators Pin
shaluka25-Apr-07 3:49
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Generalnice Pin
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