C # Four eval methods)

From: http://blog.163.com/redtomato/blog/static/48648149200831202846410/
Sometimes expression operations are required, such

String strexpression = "-12*(-2.2 + 7.7)-44*2 ";

I used codedom for searching online. For details, see

Http://www.codeproject.com/csharp/runtime_eval.asp

Simplified:

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 );

}

However, it is very slow to use. After all, real-time compilation is required.

As a result, I wrote an algorithm based on the data structure book:

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 ();

}

There are also two eval algorithms using JScript.

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 );

}

Fourth, You need to first create a JS to compile as a DLL, the following code

Import system;

Package qswhjs {

Class qswheval {

Static function eval (expression): object {return eval (expression );}

}

}

The test code is as follows:

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 ("Method 1: Expression Analysis" + d2.subtract (D1) +"

");

D1 = datetime. now;

For (I = 0; I D2 = datetime. now;

Response. Write ("Method 2: Using codecom" + d2.subtract (D1) +"

");

D1 = datetime. now;

For (I = 0; I D2 = datetime. now;

Response. Write ("method 3: using JScript + VSA" + d2.subtract (D1) +"

");

D1 = datetime. now;

For (I = 0; I D2 = datetime. now;

Response. Write ("method 4: Using JSC + DLL" + d2.subtract (D1) +"

");

}

Test results:

Method 1: analyze the expression at 00:00:00. 1702448

Method 2: Use codecom 00:00:23. 7942144

Method 3: Use JScript + VSA 00:00:00. 1902736

Method 4: Use JSC + DLL 00:00:00. 2403456

The first type is recommended here (if it is pure CSHARP)

And the third (simple code, more functions)