I am trying to learn how to embed lua in a C program, but I am not great at reading technical documents, and I haven't found any current tutorials. This is my program:
#include <iostream>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
void report_errors(lua_State*, int);
int main(int argc, char** argv) {
for (int n = 1; n < argc; ++n) {
const char* file = argv[n];
lua_State *L = luaL_newstate();
luaL_openlibs(L);
std::cerr << "-- Loading File: " << file << std::endl;
int s = luaL_loadfile(L, file);
if (s == 0) {
s = lua_pcall(L, 0, LUA_MULTRET, 0);
}
report_errors(L, s);
lua_close(L);
std::cerr << std::endl;
}
return 0;
}
void report_errors(lua_State *L, int status) {
if (status) {
std::cerr << "-- " << lua_tostring(L, -1) << std::endl;
lua_pop(L, 1);
}
}
The compiler gives undefined reference errors for luaL_newstate, luaL_openlibs, luaL_loadfilex, lua_pcallk, and lua_close. I am using Code::Blocks one a Windows computer and I have added the lua include directory to all of the search paths and liblua53.a to the link libraries. The IDE autocompleted the header names and the parser displays most of the lua functions, but with a brief search I found that the parser could not find either lua_newstate or luaL_newstate. Why does it find some of the functions and not others?
In c++ you should include lua.hpp not lua.h. lua.h does not define the extern "C" block to stop the name mangling of the c++ compiler.
The arguments for g++ had -llua before the input file. I put -llua at the end, and everything works fine now.
undefined reference to `luaL_newstate'
Need extern "C" wrapping and also as recommended above put "-llua" at the end.
extern "C" {
#include <lua5.3/lualib.h>
#include <lua5.3/lauxlib.h>
#include <lua5.3/lua.h>
}
gcc -o l -ldl l.cpp -llua5.3
Related
I've put together a very simple Lua engine but it seems to reject bytecode which works in the lua console. The uncompiled version works in the engine. Am I using luac wrong somehow?
I compile using the given command and run as './a.out'.
res/default.lua:
print("Setting up world structure.")
luac command:
luac -o res/default.lux res/default.lua
MWE:
#define SCRIPTDIR "res/"
#define THROW_IF_NONZERO(x,m) if((x)!=0) throw std::runtime_error(m);
#define THROW_IF_ZERO(x,m) if((x)==0) throw std::runtime_error(m);
extern "C" {
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"
}
#include "sys/stat.h"
#include <string>
#include <system_error>
#include <iostream>
using std::string;
class Entity {
private:
lua_State *m_lua;
public:
Entity() : Entity(nullptr) { }
Entity(lua_State *lua) : m_lua{lua} { }
virtual ~Entity() { }
void load_and_run(string);
};
class WorldEntity : public Entity {
public:
WorldEntity(lua_State *lua) : Entity(lua) {
luaL_openlibs(lua);
}
~WorldEntity() { }
};
int main() {
lua_State *lua{nullptr};
try {
lua = luaL_newstate();
WorldEntity eWorld{lua};
eWorld.load_and_run("default"); // load default.lua/lux
} catch(std::exception &e) {
if (lua != nullptr) {
lua_close(lua);
}
std::cout << "Error: " << e.what() << std::endl;
}
return 0;
}
void Entity::load_and_run(string filename) {
THROW_IF_ZERO(m_lua, "Lua not started.");
filename = SCRIPTDIR + filename + ".lux";
struct stat sb;
int rc = stat(filename.c_str(), &sb);
if (rc == -1) {
filename.pop_back();
filename += "a";
rc = stat(filename.c_str(), &sb);
THROW_IF_NONZERO(rc, "File not found!");
}
std::cout << "File: " << filename << std::endl;
// Currently won't run compiled Lua scripts, not sure why.
rc = luaL_dofile(m_lua, filename.c_str());
THROW_IF_NONZERO(rc, "Could not load lua file.");
}
compile command:
gcc src/bug001mwe.cpp -std=c++14 -llua -lstdc++
correct output from script:
File: res/default.lua
Setting up world structure.
wrong output from bytecode:
File: res/default.lux
Error: Could not load lua file.
both files, output from lua console:
Setting up world structure.
What confused me was that it worked in the lua console but not in my program. I added a call to lua_tostring after the call to luaL_dofile, like this:
rc = luaL_dofile(m_lua, filename.c_str());
std::ostringstream ostr;
ostr << "Could not load lua file. ";
ostr << lua_tostring(m_lua, -1);
THROW_IF_NONZERO(rc, ostr.str());
The error string became:
Error: Could not load lua file. res/default.lux: version mismatch in precompiled chunk
What the heck?
Long story short, I had a previous version of Lua installed due to out of date package dependencies in some unrelated stuff. The older luac was intercepting the luac command and compiling to valid but incompatible bytecode. Uninstalled the unrelated packages which I didn't really need, and now everything works.
Moral of the story: always check for an error string on the Lua stack, it will (probably) tell you what's wrong.
I try to test loading a c++ dll module in Lua using "require", below is the c++ module file
#include <stdio.h>
#include <iostream>
extern "C" {
#include "lua/lualib.h"
#include "lua/lauxlib.h"
#include "lua/lua.h"
__declspec(dllexport) int luaopen_mylib(lua_State* L);
}
using namespace std;
static int libFunc1(lua_State* L)
{
int n = lua_gettop(L);
printf("in myfunc stack, arg number: %d\n", n);
if (lua_isstring(L, -1))
{
std::cout << lua_tostring(L, -1) << std::endl;
}
else
{
std::cout << "invalid arg" << std::endl;
}
return 1;
}
static const struct luaL_Reg mylib[] = {{"func1", libFunc1}, {NULL, NULL}};
int luaopen_mylib(lua_State* L)
{
cout << "loading my lib" << endl;
luaL_newlib(L, mylib);
return 1;
}
I compiled this cpp file into dll using g++ in msys:
g++ -c -o mylib.o mylib.cpp
g++ -shared -o mylib.dll mylib.o -Llua -llua5.3.0
until now everything work fine, and I got the mylib.dll file too. but when I try to load the module, I got the error msg:
> require("mylib")
error loading module 'mylib' from file '.\mylib.dll':
找不到指定的程序。
stack traceback:
[C]: in ?
[C]: in function 'require'
stdin:1: in main chunk
[C]: in ?
the Chinese characters above mean:
The specified function could not be found.
I think the "specified function" mean the "luaopen_mylib", but the cpp file do have the function:luaopen_mylib, WHAT IS GOING WRONG?
It might be some name mangling problem. Try:
extern "C"
{
int luaopen_mylib(lua_State* L)
{
cout << "loading my lib" << endl;
luaL_newlib(L, mylib);
return 1;
}
}
I define a function In a Lua Script and call it from my C++ program. The Lua Script use cjson module. I can executes the Lua script by Lua bin, but it can't run in my C++ program.
Error Message:
error loading module 'cjson' from file '/usr/local/app/cswuyg/test_lua/install/cjson.so':
/usr/local/app/cswuyg/test_lua/install/cjson.so: undefined symbol: lua_getfield
cpp code:
extern "C"
{
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
}
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
void test_dostring(lua_State* L, const std::string& file_path) {
std::ifstream ifs;
ifs.open(file_path.c_str());
if (!ifs.is_open()) {
return ;
}
std::stringstream buffer;
buffer << ifs.rdbuf();
std::string file_info(buffer.str());
// test luaL_dostring
std::cout << luaL_dostring(L, file_info.c_str()) << std::endl;
std::cout << "error msg:" << lua_tostring(L, -1) << std::endl;
lua_getglobal(L, "comment2");
lua_pushstring(L, "xxx");
lua_call(L, 1, 0);
std::string lua_ret = lua_tostring(L, -1);
std::cout << "ret:" << lua_ret << std::endl;
}
int main(int argc, char* argv[]) {
lua_State* L = luaL_newstate();
luaL_openlibs(L);
test_dostring(L, "test.lua");
lua_close(L);
return 0;
}
Lua code:
local Json = require('cjson')
function comment2(test)
print(test)
end
comment2("xx")
How to fix it ? Any help would be appreciated.
If you're using Linux and the Lua core library is linked statically into your program, you need to expose the Lua C API by using -Wl,-E when you build your program. That's the incantation used to build the Lua command line interpreter from lua.org.
So I'm trying to load a .dylib file at runtime in c++ and calling a function within it. It does not seem to be any problem loading the file but when i try to create a function-pointer to the "print" function it's result is NULL.
Here is my code:
/* main.cpp */
#include <iostream>
#include <string>
#include <dlfcn.h>
#include "test.hpp"
int main(int argc, const char * argv[]) {
std::string path = argv[0];
std::size_t last = path.find_last_of("/");
// get path to execution folder
path = path.substr(0, last)+"/";
const char * filename = (path+"dylibs/libtest.dylib").c_str();
// open libtest.dylib
void* dylib = dlopen(filename, RTLD_LAZY);
if (dylib == NULL) {
std::cout << "unable to load " << filename << " Library!" << std::endl;
return 1;
}
// get print function from libtest.dylib
void (*print)(const char * str)= (void(*)(const char*))dlsym(dylib, "print");
if (print == NULL) {
std::cout << "unable to load " << filename << " print function!" << std::endl;
dlclose(dylib);
return 2;
}
// test the print function
print("Herro Word!");
dlclose(dylib);
return 0;
}
test dylib headerfile
/* test.hpp */
#ifndef test_hpp
#define test_hpp
void print(const char * str);
#endif
the dylib c++ file
#include <iostream>
#include "test.hpp"
void print(const char * str) {
std::cout << str << std::endl;
}
the output when running is:
unable to load /Users/usr/Library/Developer/Xcode/DerivedData/project/Build/Products/Debug/dylibs/libtest.dylib print function!
Program ended with exit code: 2
I am quite new to c++ and have never loaded dylibs before. Any help would be much appreciated!
Try qualifying the print function declaration with extern "C" to get around the name mangling that is likely going on.
Here's a nice article on the topic: http://www.tldp.org/HOWTO/C++-dlopen/theproblem.html (solution discussion on page following)
I try to test loading a c++ dll module in Lua using "require", below is the c++ module file
#include <stdio.h>
#include <iostream>
extern "C" {
#include "lua/lualib.h"
#include "lua/lauxlib.h"
#include "lua/lua.h"
__declspec(dllexport) int luaopen_mylib(lua_State* L);
}
using namespace std;
static int libFunc1(lua_State* L)
{
int n = lua_gettop(L);
printf("in myfunc stack, arg number: %d\n", n);
if (lua_isstring(L, -1))
{
std::cout << lua_tostring(L, -1) << std::endl;
}
else
{
std::cout << "invalid arg" << std::endl;
}
return 1;
}
static const struct luaL_Reg mylib[] = {{"func1", libFunc1}, {NULL, NULL}};
int luaopen_mylib(lua_State* L)
{
cout << "loading my lib" << endl;
luaL_newlib(L, mylib);
return 1;
}
I compiled this cpp file into dll using g++ in msys:
g++ -c -o mylib.o mylib.cpp
g++ -shared -o mylib.dll mylib.o -Llua -llua5.3.0
until now everything work fine, and I got the mylib.dll file too. but when I try to load the module, I got the error msg:
> require("mylib")
error loading module 'mylib' from file '.\mylib.dll':
找不到指定的程序。
stack traceback:
[C]: in ?
[C]: in function 'require'
stdin:1: in main chunk
[C]: in ?
the Chinese characters above mean:
The specified function could not be found.
I think the "specified function" mean the "luaopen_mylib", but the cpp file do have the function:luaopen_mylib, WHAT IS GOING WRONG?
It might be some name mangling problem. Try:
extern "C"
{
int luaopen_mylib(lua_State* L)
{
cout << "loading my lib" << endl;
luaL_newlib(L, mylib);
return 1;
}
}