c#四种eval方法(转)
转自:http://blog.163.com/redtomato/blog/static/48648149200831202846410/
有时候需要表达式运算，如
String strExpression="-12 * ( - 2.2 + 7.7 ) - 44 * 2";
网上找的，一般是利用CodeDom，见
http://www.codeproject.com/csharp/runtime_eval.asp
简化为：
System.CodeDom.Compiler.ICodeCompiler comp = (new Microsoft.CSharp.CSharpCodeProvider().CreateCompiler());
System.CodeDom.Compiler.CompilerParameters cp = new System.CodeDom.Compiler.CompilerParameters();
object qswhEval2(string Expression){
StringBuilder code = new StringBuilder();
code.Append("using System; \n");
code.Append("namespace ADOGuy { \n");
code.Append(" public class _Evaluator { \n");
code.Append(" public object __foo() ");
code.Append("{ ");
code.AppendFormat(" return ({0}); ", Expression);
code.Append("}\n");
code.Append("} }");
System.CodeDom.Compiler.CompilerResults cr = comp.CompileAssemblyFromSource(cp, code.ToString());
System.Reflection.Assembly a = cr.CompiledAssembly;
object _Compiled = a.CreateInstance("ADOGuy._Evaluator");
System.Reflection.MethodInfo mi = _Compiled.GetType().GetMethod("__foo");
return mi.Invoke(_Compiled, null);
}
但用起来感觉很慢，毕竟需要实时编译。
于是，就自己照数据结构书上写了一种算法：
string Precede(string p, string q){
switch(p){
case "+":
case "-":return ("*/(".IndexOf(q)!=-1)?"<":">";
case "*":
case "/":return (q=="(")?"<":">";
case "(":return (q==")")?"=":"<";
case ")":return (q=="(")?"?":">";
case "#":return (q=="#")?"=":"<";
}
return "?";
}
Double Operate(Double a,char o,Double b)
{
switch(o)
{
case '+':return a+b;
case '-':return a-b;
case '*':return a*b;
case '/':return a/b;
}
return 0;
}
Object qswhEval1(string Expression){
/*************(qiushuiwuhen 2002-12-14)****************/
Stack nArr=new Stack(),oArr=new Stack();
int j=0;
Double a=0,b=0;
string w="";
char o;
MatchCollection arr=Regex.Matches(Expression.Replace(" ","")+"#",@"(((?<=(^|\())-)?\d+(\.\d+)?|\D)");
oArr.Push('#');
w=Convert.ToString(arr[j++]);
while(!(w=="#"&&Convert.ToString(oArr.Peek())=="#")){
if("+-*/()#".IndexOf(w)!=-1){
switch(Precede(oArr.Peek().ToString(),w)){
case "<":
oArr.Push(w);
w=Convert.ToString(arr[j++]);
break;
case "=":
oArr.Pop();
w=Convert.ToString(arr[j++]);
break;
case ">":
o=Convert.ToChar(oArr.Pop());
b=Convert.ToDouble(nArr.Pop());
a=Convert.ToDouble(nArr.Pop());
nArr.Push(Operate(a,o,b));
break;
default:
return "Error";
break;
}
}else{
nArr.Push(w);
w=Convert.ToString(arr[j++]);
}
}
return nArr.Pop();
}
还有利用JScript的Eval的两种算法
Microsoft.JScript.Vsa.VsaEngine ve=Microsoft.JScript.Vsa.VsaEngine.CreateEngine();
object qswhEval3(string Expression){
return Microsoft.JScript.Eval.JScriptEvaluate(Expression,ve);
}
object qswhEval4(string Expression){
return qswhJs.qswhEval.Eval(Expression);
}
第四种需先建立一js编译为dll,如下代码
import System;
package qswhJs {
class qswhEval {
static function Eval(Expression):Object { return eval(Expression); }
}
}
测试代码如下：
void Page_Load(Object o,EventArgs ea){
String strExpression="-12 * ( - 2.2 + 7.7 ) - 44 * 2";
int i=0,c=100;
DateTime d1,d2;
cp.GenerateExecutable = false;
cp.GenerateInMemory = true;
d1=DateTime.Now;
for(i=0;i d2=DateTime.Now;
Response.Write("方法一：对表达式分析 "+d2.Subtract(d1)+"
");
d1=DateTime.Now;
for(i=0;i d2=DateTime.Now;
Response.Write("方法二：利用CodeCom "+d2.Subtract(d1)+"
");
d1=DateTime.Now;
for(i=0;i d2=DateTime.Now;
Response.Write("方法三：利用Jscript+Vsa "+d2.Subtract(d1)+"
");
d1=DateTime.Now;
for(i=0;i d2=DateTime.Now;
Response.Write("方法四：利用Jsc+Dll "+d2.Subtract(d1)+"
");
}
测试结果：
方法一：对表达式分析 00:00:00.1702448
方法二：利用CodeCom 00:00:23.7942144
方法三：利用Jscript+Vsa 00:00:00.1902736
方法四：利用Jsc+Dll 00:00:00.2403456
在此推荐第一种（如果要纯CSharp的话）
和第三种（代码简单，功能更多）
