C#.NET 動態計算運算式值

 

using System;
using System.CodeDom.Compiler;
using Microsoft.CSharp;
using System.Reflection;

namespace Pub.Class {
/// <summary>
/// 處理表達試運算---動態產生數學運算式並計算其值
/// 運算式使用 C# 文法，可帶一個的自變數(x)。
/// 運算式的自變數和值均為(double)類型。
/// </summary>
/// <example>
/// <code>
/// Expression expression = new Expression("Math.Sin(x)"); 
/// Console.WriteLine(expression.Compute(Math.PI / 2)); 
/// expression = new Expression("double u = Math.PI - x;" + 
/// "double pi2 = Math.PI * Math.PI;" + 
/// "return 3 * x * x + Math.Log(u * u) / pi2 / pi2 + 1;"); 
/// Console.WriteLine(expression.Compute(0)); 
/// 
/// Expression expression = new Expression("return 10*(5+5)/10;");
/// Response.Write(expression.Compute(0));
/// Response.End();
/// </code>
/// </example>
    public class Expression {
object instance;
        MethodInfo method;
/// <summary>
/// 表達試運算
/// </summary>
/// <param name="expression">表達試</param>
        public Expression(string expression) {
if (expression.IndexOf("return") < 0) expression = "return " + expression + ";";
string className = "Expression";
string methodName = "Compute";
            CompilerParameters p = new CompilerParameters();
            p.GenerateInMemory = true;
            CompilerResults cr = new CSharpCodeProvider().CompileAssemblyFromSource(p, string.
              Format("using System;sealed class {0}{{public double {1}(double x){{{2}}}}}",
              className, methodName, expression));
if (cr.Errors.Count > 0) {
string msg = "Expression(\"" + expression + "\"): \n";
foreach (CompilerError err in cr.Errors) msg += err.ToString() + "\n";
throw new Exception(msg);
            }
            instance = cr.CompiledAssembly.CreateInstance(className);
            method = instance.GetType().GetMethod(methodName);
        }
/// <summary>
/// 處理資料
/// </summary>
/// <param name="x"></param>
/// <returns>返回計算值</returns>
        public double Compute(double x) {
return (double)method.Invoke(instance, new object[] { x });
        }
    }
}