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CParser • Build Status License

This project provides a C++ library to parse a character sequence as an expression using Dijkstra's Shunting-yard algorithm, which modifies Jesse Brown's original code.

This project was developed by Brandon Amos and Vinícius Garcia.

Getting Started

If you want to use this library in your project please take a look at our Wiki

Builtin Features

  • Unary operators. +, -
  • Binary operators. +, -, /, *, %, <<, >>, ^, &, |, **
  • Boolean operators. <, >, <=, >=, ==, !=, &&, ||
  • Functions. sin, cos, tan, abs, print
  • Support for an hierarchy of scopes with local scope, global scope etc.
  • Easy to add new operators, operations, functions and even new types
  • Easy to implement object-to-object inheritance (with the prototype concept)
  • Built-in garbage collector (does not handle cyclic references yet)


Download and Compile

cd 'my/project/dir'
git clone
make release -C cparse

Link with your project:

g++ -I cparse -std=c++11 cparse/builtin-features.o cparse/core-shunting-yard.o main.cpp -o main

Running the library tests:

If you want to make sure everything is working in your environment:

make test -C cparse

Customizing your Library

To customize your calculator:

  1. Copy the builtin-features.cpp file and builtin-features/ directory to your project.
  2. Edit the builtin-features/*.inc files as you like.
  3. Then build the project:
    1. Compile the library: make release -C cparse/
    2. Compile your modified features: g++ -I cparse -std=c++11 -c builtin-features.cpp -o my-features.o
    3. Link your project: g++ -I cparse -std=c++11 my-features.o cparse/core-shunting-yard.o main.cpp -o main

For a more detailed guide read our Wiki advanced concepts' section:

Minimal examples

As a simple calculator

#include <iostream>
#include "shunting-yard.h"

int main() {
  TokenMap vars;
  vars["pi"] = 3.14;
  std::cout << calculator::calculate("-pi+1", &vars) << std::endl;

  // Or if you want to evaluate an expression
  // several times efficiently:
  calculator c1("pi-b");
  vars["b"] = 0.14;
  std::cout << c1.eval(vars) << std::endl; // 3
  vars["b"] = 2.14;
  std::cout << c1.eval(vars) << std::endl; // 1

  return 0;

As a sub-parser for a programming language

Here we implement an interpreter for multiple expressions, the delimiter used will be ; or \n just like Javascript or Python and the code must start and end on curly brackets.

A similar architecture can be used for interpreting other common programming language statements like for loops and if statements. If you're interested take a look on the jSpy programming language that uses this project as the core parsing system.

#include <iostream>
#include "shunting-yard.h"
#include "shunting-yard-exceptions.h"

struct codeBlock {
  static void interpret(const char* start, const char** end, TokenMap vars) {
    // Remove white spaces:
    while (isspace(*start)) ++start;

    if (*start != '{') {
      throw syntax_error("Expected '{'");
    } else {

    while (*start != '}') {
      calculator::calculate(start, vars, ";\n}", &start);

      // Alternatively you could write above:
      // - calculator(start, ";\n}", &start).eval(vars);

      // Find the beginning of the next expression:
      while(isspace(*start) || *start == ';') ++start;

    if (*start == '}') {
      *end = start+1;
    } else {
      throw syntax_error("Expected '}'");

int main() {
  GlobalScope vars;
  const char* code =
    "  a = 10;"
    "  b = 20\n"
    "  c = a + b }";

  codeBlock::interpret(code, &code, vars);

  std::cout << vars["c"] << std::endl; // 30
  return 0;

Please note that a calculator can compile an expression so that it can efficiently be executed several times at a later moment.

More examples

  • For more examples and a comprehensible guide please read our Wiki


  • I would like to keep this library minimal so new features should be very useful to be accepted.
  • If proposed change is not a common use case, I will probably not accept it.


A C++ configurable Expression Parser. Useful as a Calculator or for helping you write your own Programming Language








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