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C# Eval Function

, 21 Jun 2007
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C# eval function

Introduction

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 object.property), 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

Basic

2+3*5
 true||false
 a+b*c
 a.b+c.d
 a.f(1,2)[b]
 "123"[0]
 "123".Length
 (1).ToString()

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:

string.Format("{0}1111",233)

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

Advanced

(a>b)?c:d 

Reflection

("To"+"String")()

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))
                    break;
                try
                {
                    Tree tree = ep.Parse(line);

                    tree.Print(System.Console.Out);

                    object result = evaluater.Eval(tree);

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

License

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

About the Author

devilplusplus
Web Developer
China China
No Biography provided

Comments and Discussions

 
QuestionBug in Scanner.cs, at line 453 PinmemberMember 864646714-Feb-12 7:42 
QuestionThanks Pinmemberbildik9-Aug-11 10:58 
GeneralMy vote of 5 PinmemberChenNoam4-Oct-10 21:17 
GeneralGracias! PinmemberMember 44952424-Jun-10 6:00 
Generalthanks! Pinmemberbpbrainiak4-May-10 4:00 
GeneralRounding problem PinmemberPauline Cole30-Nov-09 11:20 
GeneralCalculation bug with negative numbers PinmemberPauline Cole11-Oct-09 23:51 
GeneralRe: Calculation bug with negative numbers Pinmemberbpbrainiak4-May-10 3:56 
GeneralNice PinmemberKeitaroSan8-Oct-09 7:17 
GeneralDon't use it for work, only for learning stuff PinmemberDannie Juge30-Sep-09 3:25 
QuestionParse as decimal values Pinmemberpalswim15-Jun-09 11:35 
AnswerRe: Parse as decimal values Pinmemberpalswim15-Jun-09 11:37 
GeneralLicense PinmemberMember 256327611-May-09 3:54 
GeneralRe: License Pinmemberdevilplusplus30-May-09 15:30 
GeneralOne slight correction in the test code PinmemberAndrew Kaiser26-Nov-08 2:26 
GeneralCalculation Error Pinmemberpauf15-Nov-08 0:42 
QuestionAssign Variables Pinmemberj_jpg12-Nov-08 0:54 
GeneralGreat work PinmemberChenNoam5-Nov-08 22:44 
Generalcan't parse Pinmemberjameswei1-Oct-08 16:43 
AnswerRe: can't parse PinmemberChenNoam5-Nov-08 22:47 
Questionis it possible to add variable in runtime ? Pinmembernaamakat25-May-08 2:15 
GeneralGetting data from a deep object Pinmemberftuttle13-May-08 7:05 
QuestionLicense PinmemberKjell Ahlstrom2-Mar-08 22:10 
GeneralRe: License Pinmemberdevilplusplus8-Apr-08 14:09 
NewsScript.NET PinmemberExtrim18-Oct-07 6:09 

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