Lua Example

main.cpp

#include <iostream>
#include <vector>

#ifdef __cplusplus
  extern "C" {
    #include <lua.h>
    #include <lualib.h>
    #include <lauxlib.h>
  }
#endif

static uint8_t* g_packet_ptr;
static uint32_t g_packet_size;


int getByte(lua_State *L) {
    unsigned int index = luaL_checkinteger(L, 1);

    if (index < g_packet_size) {
        lua_pushinteger(L, g_packet_ptr[index]);
    } else {
        lua_pushnil(L);
    }
    return 1; // Number of return values
}

int packetSize(lua_State *L) {
    lua_pushinteger(L, g_packet_size);
    return 1;
}

int main() {
    lua_State* L = luaL_newstate(); // Create a new Lua state
    luaL_openlibs(L);              // Load Lua libraries
    lua_register(L, "getByte", getByte);
    lua_register(L, "packetSize", packetSize);

    
    {
        // My new packet    
        std::vector<uint8_t> packet_data = {10,45,13,1,45,201,32};
        
        // Set globals to point to new packet - don't copy the data
        g_packet_ptr = packet_data.data();
        g_packet_size = packet_data.size();
            
        const char *luaScript1 = R"(
            local value = getByte(3)
            if value then
                print("Value at index 3: " .. value)
            else
                print("Index out of range")
            end
        )";
        
        
        if (luaL_dostring(L, luaScript1) != LUA_OK) {
            std::cerr << "Failed to run Lua script: " << lua_tostring(L, -1) << std::endl;
        }

        const char *luaScript2 = R"(if packetSize() > 5 and getByte(0) == 10 and getByte(4) == 45 then print("Match") end)";
        
        if (luaL_dostring(L, luaScript2) != LUA_OK) {
            std::cerr << "Failed to run Lua script: " << lua_tostring(L, -1) << std::endl;
        }
        
        // Reset Globals
        g_packet_ptr = nullptr;
        g_packet_size = 0;
    }

    lua_close(L);
    return 0;
}

Makefile

# Compiler and flags
CXX := g++
CXXFLAGS := -Wall -std=c++11 -I./lua

# Directories
LUA_DIR := ./lua
SRC_DIR := .

# Files
SRC := $(wildcard $(SRC_DIR)/*.cpp)
OBJ := $(SRC:$(SRC_DIR)/%.cpp=$(SRC_DIR)/%.o)
LUA_SRC := $(wildcard $(LUA_DIR)/*.c)
PROG_NAME := my_app

# Build the final executable
$(PROG_NAME): $(OBJ) $(LUA_DIR)/liblua.a
	$(CXX) $(CXXFLAGS) -o $(PROG_NAME) $^ -ldl -lm

# Compile any C++ source files into object files
%.o: %.cpp
	$(CXX) $(CXXFLAGS) -c $< -o $@

# Build statically linkable lua lib
$(LUA_DIR)/liblua.a: $(LUA_SRC)
	$(MAKE) -C $(LUA_DIR) a

all: $(PROG_NAME) 

clean:
	$(MAKE) -C $(LUA_DIR) clean
	rm $(PROG_NAME) $(OBJ)

# Phony targets
.PHONY: clean all