jgod / eval

A simple, header-only, expression parser for C++11.

eval

Eval is a simple, header-only, expression parser for C++.

features

• easy to integrate - just include eval.h
• simple API: eval("your expression", ?vars, ?functions)
• operators * / + - ^ %
• numbers and strings
• variable argument functions
• built-in constants and functions like pi, sqrt(), sin(), ceil() etc.
• tests

requirements

C++11 compiler

usage

basic

#include "eval.h"
using namespace jgod;

assert(eval("3*2 + 4") == 10);

vars

std::map<std::string, double> vars;
vars["myvar"] = 2;
assert(eval("3*myvar + 4", vars) == 10);

error handling

try {return eval("3.14q59");}
catch (const std::invalid_argument &e) {...}

impl details

• flow
  1. strip whitespace
  2. rewrite adjacent operators
  3. tokenize
  4. Shunting-yard algorithm to build RPN queue
  5. process queue with RPN calculator
• values: numbers and strings
  • base value type is std::string (casts are necessary)
  • numbers == doubles
  • "null" expressions return 0
• unary + -
• function binding using std::function
• variable length functions using std::vector
• std::exceptions for error handling

license

Copyright Justin Godesky. Released under the AGPLv3 License.