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C++ Mathematical Expression Evaluator

A powerful, header-only C++ library for parsing and evaluating mathematical expressions

✨ Features

• Header-only – Zero compilation overhead, easy integration
• Type Flexible – Works with any numeric type (double, float, int, etc.)
• Character Support – Full support for narrow (char) and wide (wchar_t) strings
• Variable Management – Add, get, set, find variables with ease
• Operator Control – Define custom operators with precedence and associativity
• Function Library – 30+ built-in mathematical functions
• Custom Functions – Create functions with variable number of arguments
• Smart Memory – RAII-compliant with shared_ptr support

🔧 Requirements

• C++11 or later
• Standard Template Library (STL)
• No external dependencies

📥 Installation

1. Download eval.hpp, eval_core.hpp and options.hpp
2. Place them in your project's include directory
3. Include eval.hpp in your source files
4. Compile with C++11 support enabled

#include "eval.hpp"

🚀 Quick Start

Basic Arithmetic

#include "eval.hpp"
#include <iostream>

using namespace ydog01::eval;

int main()
{
    Evaluator<char, double> eval(Options::All);
    double result = eval("2 * 3 + 1");
    std::cout << "Result: " << result << std::endl;
    return 0;
}

With Variables

Evaluator<char, double> eval(Options::All);
eval.add_variable("x", 10.0);
eval.add_variable("y", 20.0);
double result = eval("x + y");
std::cout << result << std::endl;

eval.set_variable("x", 100.0);
result = eval("x + y");
std::cout << result << std::endl;

Custom Function

Evaluator<char, double> eval(Options::All);

eval.add_function("max", [](core::ParamViewer<double> a) {
    double m = a[0];
    for (size_t i = 1; i < a.size(); ++i)
        if (a[i] > m) m = a[i];
    return m;
});

double result = eval("max(10, 20, 30, 5)");
std::cout << result << std::endl;

Custom Operator

Evaluator<char, double> eval;
eval.enable_whitespace_skip();
eval.enable_constant_parser();
eval.enable_function_call();

eval.add_prefix("!", [](core::ParamViewer<double> a) {
    int n = static_cast<int>(a[0]);
    double r = 1;
    for (int i = 2; i <= n; ++i) r *= i;
    return r;
}, 40);

double result = eval("!5");
std::cout << result << std::endl;

📖 API Reference

Configuration

Method	Description
enable_whitespace_skip(bool)	Skip whitespace characters
enable_constant_parser(bool)	Parse numeric constants
enable_function_call(bool)	Enable parentheses and comma

Variable Operations

Method	Description
add_variable(name, value)	Add a variable
add_variable(name, ptr)	Add a variable from pointer
get_variable(name)	Get variable reference
set_variable(name, value)	Modify variable
find_variable(name)	Find variable, returns pointer

Operator Registration

Method	Description
add_prefix(name, func, prec, assoc)	Register prefix operator
add_infix(name, func, prec, assoc)	Register infix operator
add_suffix(name, func, prec, assoc)	Register suffix operator
add_function(name, func, assoc)	Register function

Removal

Method	Description
remove_variable(name)	Remove variable
remove_prefix(name)	Remove prefix operator
remove_infix(name)	Remove infix operator
remove_suffix(name)	Remove suffix operator

Evaluation

Method	Description
parse(expr)	Parse expression, return Expression object
evaluate(expr)	Parse and evaluate
operator()(expr)	Same as evaluate

Built-in Functions

Category	Functions
Basic Ops	+ - * / % ^
Constants	pi e
Trig	sin cos tan asin acos atan atan2
Hyperbolic	sinh cosh tanh asinh acosh atanh
Exp/Log	exp exp2 ln log log10 log2 log1p
Power/Root	sqrt cbrt hypot
Rounding	ceil floor round trunc abs
Special	erf erfc tgamma lgamma

Options

Option	Value	Description
None	0	No features
WhitespaceSkip	1	Skip whitespace
ConstantParser	2	Parse numbers
Parentheses	4	Support parentheses
Comma	8	Support comma
BuiltinOps	16	Built-in operators
BuiltinConstants	32	Built-in constants
BuiltinFuncs	64	Built-in functions
All	127	Enable all features

🎯 Advanced Examples

Nested Function Calls

Evaluator<char, double> eval(Options::All);
eval.add_function("max", [](auto a) {
    double m = a[0];
    for (size_t i = 1; i < a.size(); ++i)
        if (a[i] > m) m = a[i];
    return m;
});
double result = eval("max(sin(pi/2), cos(0), tan(pi/4))");

Complex Expressions

double result = eval("(2+3)*4 - 5/2 + sin(pi/2)");
double result2 = eval("sqrt( (2^3 + 4^2) / 2 )");

⚠️ Error Handling

try {
    double result = eval("invalid expression");
} catch (const std::runtime_error& e) {
    std::cerr << "Error: " << e.what() << std::endl;
}

🤝 Contributing

Contributions welcome! Submit pull requests or open issues for bugs and feature requests.