Simple library or implementation for a mathematical expression evaluator [closed]

Answer 1

For c++, try out muParser:

muParser - a fast math parser library

Answer 2

For C et al, here's a quick-n-dirty and highly unsafe cheat that requires Perl:

double eval(const char* expr) {
    char buf[1024];
    snprintf(buf, sizeof(buf), "perl -e 'print (%s)'", expr);
    FILE* p = popen(buf, "r");
    double d;
    fscanf(p, "%lf", &d);
    fclose(p);
    return d;
}

Answer 3

.NET solutions:

Here couple of topics on SO:

• c# evaluating string “3*(4+2)” yield int 18
• Is it possible to translate a user-entered mathematical equation into C# code at runtime?
• Is there a string math evaluator in .NET?
• Best and shortest way to evaluate mathematical expressions
• C# Math calculator (closed)

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Also two projects I already used brefore:

C#: NCalc - Mathematical Expressions Evaluator for .NET

NCalc is a mathematical expressions evaluator in .NET. NCalc can parse any expression and evaluate the result, including static or dynamic parameters and custom functions.

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VB.NET: Fast Lightweight Expression Evaluator

Flee is an expression parser and evaluator for the .NET framework. It allows you to compute the value of string expressions such as sqrt(a^2 + b^2) at runtime. It uses a custom compiler, strongly-typed expression language, and lightweight codegen to compile expressions directly to IL. This means that expression evaluation is extremely fast and efficient. Try out the demo, which lets you generate images based on expressions, and see for yourself.

You can use it with C# since it .NET anyway (via assembly reference).

Answer 4

I'd consider embedding lua. Its fast, lightweight and ansi C. And its been specifically designed for embedding. Used by many games as their scripting language. (IMO much easier to embed than python or perl)

Here's a complete example to show how trivial it is

extern "C"
{
  #include "lua.h"
  #include "lauxlib.h"
  #include "lualib.h"
}

#include <string>
#include <iostream>

int main()
{
   std::string expression = "12+(3.0*(4)-1)/math.sqrt(121)";
   lua_State * L = lua_open();
   luaopen_math(L);
   if( luaL_dostring(L, ("return "+expression).c_str()) != 0 )
   {
      std::cout<<"ERROR : "<<lua_tostring(L,-1)<<std::endl;
   }
   if( lua_type(L,-1) == LUA_TNUMBER )
   {
      std::cout<<"GOT "<<lua_tonumber(L,-1)<<std::endl;
   }
   lua_close(L);
}

Answer 5

In The UNIX Programming Environment, I think it was, a simple calculator called hoc (IIRC) was developed. Possibly its source code is available just about anywhere.

Cheers & hth.,

Answer 6

If you care to brave the source code, you can always look at bc. It handles all the Lex/Yacc goodness for you. And if you want a pure C++ solution, you can try coding in Boost Spirit.