This is a tiny numerical expression evaluator, intended for embedding in C++ program.
#include "tecalc.hpp"
tecalc::calculator calc;
calc.bind_var("A", 2).bind_var("B", 4);
int res1 = calc.eval("(1 + A) * B - 2");
// res1 == 10
calc.bind_fn("abs", [](int x){ return x < 0 ? -x : x; })
.bind_fn("min", [](int a, int b){ return a < b ? a : b; });
int res2 = calc.eval("abs(min(-A, -B))");
// res2 = 4The tecalc evaluator supports;
- basic arithmetic operators such as
+,-,*,/,%(modulo) and parentheses, - decimal/hexadecimal(
0x)/binary(0b) number literals, - binding a value to variable name, and user-defined function call.
The eval uses single-pass algorithm, builds no AST (abstract syntax tree),
parses and evaluates input expressions simultaneously.
- C++17 or later
namespace tecalc {
// error codes
enum class errc {...};
// exception throw by eval()
class tecalc_error : public std::runtime_error {
const std::error_code& code();
// (and inherited from std::runtime_error)
};
template <class Value, int MaxArgNum = 2>
class basic_calculator {
using value_type = Value;
using func_type = std::variant</*see below*/>;
// std::variant of function types that different number of parameters
// Value(*)(), Value(*)(Value), Value(*)(Value,Value), ...
// evaluate expression string, return optional<Value> or error_code
std::optional<value_type> eval(std::string_view expr, std::error_code& ec);
// evaluate expression string, return Value or throw tecalc_error
value_type eval(std::string_view expr);
// bind value to variable name
basic_calculator& bind_var(std::string name, value_type val);
// bind function pointer to function name
basic_calculator& bind_fn(std::string name, func_type fn);
};
using calculator = basic_calculator<int>;
}expression := addsub-expr
addsub-expr := muldiv-expr {'+'|'-' muldiv-expr}*
muldiv-expr := unary-expr {'*'|'/'|'%' unary-expr}*
unary-expr := {'+'|'-'}* postfix-expr
postfix-expr := primary-expr {'(' arguments? ')'}?
arguments := addsub-expr {',' addsub-expr}*
primary-expr := {'(' addsub-expr ')'} | integer | identifier
integer := {digit}+ // decimal
| {"0x"|"0X"} {digit | 'a'|...|'f' | 'A'|...|'F'}+ // hexadecimal
| {"0b"|"0B"} {'0'|'1'}+ // binary
identifier := alphabet {alphabet | digit}* // variable or function
digit := '0'|...|'9'
alphabet := 'a'|...|'z' | 'A'|...|'Z'
MIT License