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A powerful function parser

, 22 Feb 2000
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A simple yet powerful function parser that parses and evaluates standard mathematical functions
  • Download source files - 82 Kb
  • The inspiration to write this code was to have an easy-to-use parser for functions given as string. You have a string like "cos(x)-7*x/(1+x)", and you want to compute some values, maybe for displaying the graph of the function. You can write code like this:

    CFunction<long double>* fkt = CFunction<long double>::Parse("cos(x)-7*x/(1+x)");
    long double y = fkt->Execute(1.5);

    There are lots of definitions in the background, but the result is easy and fast! There is a one-time pasing step to construct the function tree, and function evaluations are only calls of standard math functions like sin, +, *, sqrt. When you want to know details about the implementaion, you should look into the source code. It would be too complex to describe the parsing algorithm here.

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    About the Author

    Andreas Jäger
    Web Developer
    Germany Germany
    No Biography provided

    Comments and Discussions

     
    GeneralMFC compile PinmemberLuke Murphey6-Jul-02 10:28 
    GeneralRe: MFC compile PinmemberlLukeMurphey8-Jul-02 7:56 
    GeneralA version without MFC / MS dependencies PinmemberJochenKa14-Feb-02 21:23 
    GeneralRe: A version without MFC / MS dependencies Pinmemberjean-luc adam19-Feb-02 2:50 
    GeneralRe: A version without MFC / MS dependencies PinmemberJochen Kalmbach29-Jan-04 20:31 
    GeneralRe: A version without MFC / MS dependencies PinmemberPhilippe Lhoste4-Dec-04 3:25 
    GeneralRe: A version without MFC / MS dependencies PinmemberJochen Kalmbach [MVP VC++]1-Jan-06 20:58 
    GeneralRe: A version without MFC / MS dependencies PinmemberMember 190613125-Jul-13 14:18 
    Generalmore General expression PinmemberJie Luo16-Jan-02 2:56 
    GeneralWorld peace PinmemberBartosz Bien14-Dec-01 14:14 
    GeneralTo B.Starks, W.Dean, & J.Andreas PinmemberAmit Gefen8-Nov-01 13:43 
    GeneralOperators/precedence/types etc PinmemberAndrew Phillips26-Sep-01 19:04 
    GeneralVery good success with this PinmemberJeff12-May-01 9:59 
    GeneralYou must read jeff's reply..!! then you will success PinmemberJsSong25-Mar-02 15:47 
    GeneralBugs etc below should be renamed to Dean Wyant knows little about programming. PinmemberB. Starks13-Apr-01 8:36 
    To Dean Wyant,
     
    I nearly didn't bother trying FunctionParser due to your scathing review. However, I'm glad I recognized that Dean simply doesn't know very much and talks too much. I went ahead and tried FunctionParser and found it to be good.
     
    The issue with the '.' changed to ',' as almost all experienced programmers know, is due to Locale settings (the code was written in Germany, you are in the U.S.). Simply comment out the line that replaces the '.' with ','.
     
    Next the issue you have with it not being able to parse (x*3.5) / (x*x) is due to the fact that the author wrote a quick and dirty using std::cin which everyone knows will stall on the ' ' in front of the '/'. This isn't a problem if you simply don't use std::cin for input from the user. You can't blame the author for this either because he was simply trying to provide a demonstration app quickly, however he could clear this up by not using cin.
     
    I find the Parser to be a good one and thank the author for sharing it, and gladly accept any problems it may have. To Dean Wyant I suggest that you should evaluate your own programming abilities before railing on someone for providing great code that is simply above your abilities to understand.
     
    Sincerely,
     
    B. Starks
    b_starks@hotmail.com
    GeneralRe: Bugs etc below should be renamed to Dean Wyant knows little about programming. PinmemberDean Wyant30-Apr-04 11:11 
    GeneralA good Parser Pinmemberstocklab18-Jan-01 18:57 
    GeneralRe: A good Parser PinmemberPing He10-May-01 0:36 
    GeneralRe: A good Parser PinmemberMathePeter3-Jul-07 4:22 
    GeneralDoes not understand decimals PinsussAnonymous3-Nov-00 5:55 
    QuestionBugs etc. - How does it deserve such high ratings? PinsussDean Wyant23-May-00 14:59 
    QuestionEnglish translation of comments? PinsussPeter Helmers10-Apr-00 5:03 
    GeneralFunctionParser PinsussArmin Zürcher12-Mar-00 2:57 

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