A powerful function parser

Andreas Jäger

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22 Feb 2000

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A simple yet powerful function parser that parses and evaluates standard mathematical functions

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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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Written By

Andreas Jäger

Web Developer

Germany

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Comments and Discussions

I am working on a port of UNIX Xspread to windows. I am attempting to integrate this code into my MFC application, however, I cannot get it to compile. Below is the code snippet intended to get the result:

CString Expression;

//Call the math parser, get the function result and set the cell value to the result
CFunction<long double="">* bob = CFunction<long double="">::Parse(m_strText);
Expression = bob->GetName();

Note: when I post this message to this site, the template prefix argument keeps disappearing (strange). CFunction has a template argument of long double (so does the scope for the call to Parse). This is OK in my application.

Here is the errors:

C:\My Documents\MyProjects\Xspread32\xspread32\Grid_src\GridCell.cpp(212) : error C2065: 'CFunction' : undeclared identifier
C:\My Documents\MyProjects\Xspread32\xspread32\Grid_src\GridCell.cpp(212) : error C2062: type 'long double' unexpected
C:\My Documents\MyProjects\Xspread32\xspread32\Grid_src\GridCell.cpp(212) : error C2039: 'Parse' : is not a member of '`global namespace''
C:\My Documents\MyProjects\Xspread32\xspread32\Grid_src\GridCell.cpp(213) : error C2065: 'bob' : undeclared identifier
C:\My Documents\MyProjects\Xspread32\xspread32\Grid_src\GridCell.cpp(213) : error C2227: left of '->GetName' must point to class/struct/union

I did include the header files, and the IDE does display that the object "func" is a CFunction object (i.e. when you hover the cursor over the object name in MVC++ 6). I just can't make a connnection between my code and this math parser. I downloaded the command line code and it compiles with no problems. I created a new MFC project and tried to integrate the parser in the same manner as the console code that worked & I got the same errors. I am relatively new to MFC (not new to C++ however) and I could use any help I can get.

Luke

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