字符串计算表达式

 1  public class Expression
 2     {
 3         object instance;
 4         MethodInfo method;
 5         /// <summary>
 6         /// 表达试运算
 7         /// </summary>
 8         /// <param name="expression">表达试</param>
 9         public Expression(string expression)
10         {
11             if (expression.IndexOf("return") < 0) expression = "return " + expression + ";";
12             string className = "Expression";
13             string methodName = "Compute";
14             CompilerParameters p = new CompilerParameters();
15             p.GenerateInMemory = true;
16             CompilerResults cr = new CSharpCodeProvider().CompileAssemblyFromSource(p, string.
17               Format("using System;sealed class {0}{{public double {1}(double x){{{2}}}}}",
18               className, methodName, expression));
19             if (cr.Errors.Count > 0)
20             {
21                 string msg = "Expression(\"" + expression + "\"): \n";
22                 foreach (CompilerError err in cr.Errors) msg += err.ToString() + "\n";
23                 throw new Exception(msg);
24             }
25             instance = cr.CompiledAssembly.CreateInstance(className);
26             method = instance.GetType().GetMethod(methodName);
27         }
28         /// <summary>
29         /// 处理数据
30         /// </summary>
31         /// <param name="x"></param>
32         /// <returns>返回计算值</returns>
33         public double Compute(double x)
34         {
35             return (double)method.Invoke(instance, new object[] { x });
36         }