I'm trying to export a simple class to Lua using LuaBind. I took the code from two sites which showed roughly the same way to do it, but it's still failing.
// Default headers
#include <iostream>
#include <string>
// Lua headers
extern "C" {
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
}
#include "luabind/luabind.hpp"
// Sample class
class NumberPrinter
{
public:
NumberPrinter( int number ) : m_number( number ) {}
void print() { std::cout << m_number << "\n"; }
private:
int m_number;
};
int main() {
// Create Lua state and load sample file
lua_State *luaState = lua_open();
luabind::open( luaState );
// Set up bind to number class
luabind::module( luaState ) [
luabind::class_<NumberPrinter>( "NumberPrinter" )
.def( luabind::constructor<int>() )
.def( "print", &NumberPrinter::print )
];
// Use the class in Lua
luaL_dostring( luaState,
"Print2000 = NumberPrinter(2000)\n"
"Print2000:print()\n"
);
// Clean up Lua state
lua_close( luaState );
getchar();
return 0;
}
When running that code, luabind::module causes the following runtime error and has no other information in debug mode:
Unhandled exception at 0x690008f5 in
Lua Playground.exe: 0xC0000005: Access
violation.
I would encourage you to get this started with the binaries and sample VS2008 solution available from this website. It has the exact same sample code you are trying to run (minus the typos) and it worked well on my machine. If it still doesn't work, you'll need help from the Lua community. A minidump is probably required to help them diagnose this, just the exception message isn't enough.
Related
So I've got this interface class that I include, both in the dll and the client project
// InterfaceClass.h
#pragma once
class InterfaceClass
{
public:
virtual void Update() = 0;
};
This is the dll class that calls one of its own methods inside update
// DLLClassThatDoesSomething.cpp
#include "InterfaceClass.h"
#include <iostream>
#include <string>
class __declspec(dllexport) DLLClass : public InterfaceClass
{
public:
void Update()
{
std::cout << this->GetString();
}
std::string& GetString()
{
std::string thestring = "bruhmoment";
return thestring;
}
};
extern "C"
{
__declspec(dllexport) InterfaceClass* CreateInstance()
{
return new DLLClass();
}
}
And this is the "Client" project
// main.cpp
#include "InterfaceClass.h"
#include <Windows.h>
typedef InterfaceClass* (__cdecl *Class) ();
int main()
{
HINSTANCE dll = LoadLibrary(L"DLLClass.dll");
Class klass = (Class)GetProcAddress(dll, "CreateInstance");
InterfaceClass* IKlass = klass();
IKlass->Update();
FreeLibrary(dll);
return 0;
}
The moment I call IKlass->Update() I get an exception for Access Memory Violation because of the DLLClass calling its own method.
I haven't tried anything since I barely know how to load a DLL on runtime and I've used this nifty tutorial
How can I let it call the method and not get thrown an exception? I'm trying to let ppl that will create mods for my game create their own mods with their custom classes for bosses, mobs and etc. in DLLs.
EDIT:
Turns out it was a syntax mistake on my end. Instead of return new DLLClass;, it had to be return new DLLClass();. After fixing it, it works as intended.
You return a reference to a local variable thestring, and by the time you try to access it in
std::cout << this->GetString(), referenced data is already destroyed. In fact, it is destroyed right after the end of enclosing scope of compound statement where the variable was declared.
It may "appear" to work sometimes due to the stack not being overwritten yet, but eventually it will fail miserably like it did in your case. This triggers UB (undefined behavior).
Overview
I am trying to develop a C++ application which allows for user-created plugins.
I found a nice library called Pluma (http://pluma-framework.sourceforge.net/) which functionally seems to be exactly what I want.
After going through their tutorial, I was able to (with a bit of difficulty) convince the plugin to compile. However, it refuses to play nice and connect with the main program; returning various errors depending on how I try to implement them.
Problem
If I comment out the line labeled 'Main problem line' (in the last file, main.cpp), the plugin compiles successfully, and the main app can recognize it, but it says that "Nothing registered by plugin 'libRNCypher'", and none of the functions can be called.
If I compile that line, the main application instead says "Failed to load library 'Plugins/libRNCypher.so'. OS returned error: 'Plugins/libRNCypher.so: undefined symbol: _ZTIN5pluma8ProviderE".
My guess is that it has something to do with the way the plugin was compiled, as compiling it initially did not work and Code::Blocks told me to compile with "-fPIC" as a flag (doing so made it compile).
Code
Code below:
Main.cpp
#include "Pluma/Pluma.hpp"
#include "CryptoBase.h"
int main()
{
pluma::Pluma manager;
manager.acceptProviderType< CryptoBaseProvider >();
manager.loadFromFolder("Plugins", true);
std::vector<CryptoBaseProvider*> providers;
manager.getProviders(providers);
return 0;
}
CryptoBase.h
#ifndef CRYPTOBASE_H_INCLUDED
#define CRYPTOBASE_H_INCLUDED
#include "Pluma/Pluma.hpp"
#include <string>
#include <vector>
#include <bitset>
//Base class from which all crypto plug-ins will derive
class CryptoBase
{
public:
CryptoBase();
~CryptoBase();
virtual std::string GetCypherName() const = 0;
virtual std::vector<std::string> GetCryptoRecApps() const = 0;
virtual void HandleData(std::vector< std::bitset<8> > _data) const = 0;
};
PLUMA_PROVIDER_HEADER(CryptoBase)
#endif // CRYPTOBASE_H_INCLUDED
RNCypher.h (This is part of the plugin)
#ifndef RNCYPHER_H_INCLUDED
#define RNCYPHER_H_INCLUDED
#include <string>
#include <vector>
#include <bitset>
#include "../Encoder/Pluma/Pluma.hpp"
#include "../Encoder/CryptoBase.h"
class RNCypher : public CryptoBase
{
public:
std::string GetCypherName() const
{
return "RNCypher";
}
std::vector<std::string> GetCryptoRecApps() const
{
std::vector<std::string> vec;
vec.push_back("Storage");
return vec;
}
void HandleData(std::vector< std::bitset<8> > _data) const
{
char letter = 'v';
_data.clear();
_data.push_back(std::bitset<8>(letter));
return;
}
};
PLUMA_INHERIT_PROVIDER(RNCypher, CryptoBase);
#endif // RNCYPHER_H_INCLUDED
main.cpp (This is part of the plugin)
#include "../Encoder/Pluma/Connector.hpp"
#include "RNCypher.h"
PLUMA_CONNECTOR
bool connect(pluma::Host& host)
{
host.add( new RNCypherProvider() ); //<- Main problem line
return true;
}
Additional Details
I'm compiling on Ubuntu 16.04, using Code::Blocks 16.01.
The second error message seems to not come from Pluma itself, but a file I also had to link, #include <dlfcn.h> (which might be a Linux file?).
I would prefer to use an existing library rather than write my own code as I would like this to be cross-platform. I am, however, open to any suggestions.
Sorry for all of the code, but I believe this is enough to reproduce the error that I am having.
Thank You
Thank you for taking the time to read this, and thank you in advance for your help!
All the best, and happy holidays!
I was not able to reproduce your problem, however looking at
http://pluma-framework.sourceforge.net/documentation/index.htm,
I've noticed that:
in your RNCypher.h file you miss something like
PLUMA_INHERIT_PROVIDER(RNCypher, CryptoBase)
it seems also that there's no file CryptoBase.cpp containing something like
#include "CryptoBase.h"
PLUMA_PROVIDER_SOURCE(CryptoBase, 1, 1);
finally, in CryptoBase.h I would declare a virtual destructor (see Why should I declare a virtual destructor for an abstract class in C++?) and provide a definition to it, while you should not declare a default constructor without providing a definition to it (see for instance Is it correct to use declaration only for empty private constructors in C++?); of course the last consideration is valid unless there's another file in which you have provided such definitions.
I am new c++ so forgive me to be asking this question. I created a project and run it the first time, it is successful. But when i start another project and i added 4 classes to it (you can see from the tabs) and the main.cpp is unable to run. I am confused as the codes are exactly the same in both projects.
Run Successful:
Success
Build Successful but run failed:
Run Failed
What are the solutions to solve this problem?
Do i have to post codes of all my classes? (there are 8 files)
student.h:
#ifndef CLSSTUDENT_H
#define CLSSTUDENT_H
#include <string>
#include <iostream>
using namespace std;
class clsStudent {
protected:
string name;
string student_no;
string program;
public:
clsStudent(string n, string sn,string prog );
virtual void displayStudentDetails();
};
student.cpp
#include "TutorialClass.h"
void TutorialClass::addStudent(clsStudent std)
{
_students.push_back(std);
}
int TutorialClass::getStudentCount()
{
return _students.size();
}
void TutorialClass::display()
{
}
#endif /* CLSSTUDENT_H */
I open up a new project and added only this class. It is unable to run as well. What is the problem in the codes?
It seems that your program only fails to run when it's compiled with other files. My bet is that in these files you've got buggy code that is running before main() gets to run.
This can happen in cases like this:
int f() {
throw; // bam! Uncaught exception;
}
int x = f(); // this runs before main()
Or this:
class C {
C() {
cout << "This runs before main() too!" << endl;
}
};
C my_c; // calls constructor
In both cases: code was executed before main(). You want this because you want your global variables to be initialized before running main(). If this initialization code manages to crash the program via a segfault or an exit() call or throwing some exception which isn't caught? You've got a crashed program before it ever even gets the chance to run.
This has been driving me nuts for a long time now. I have followed every tutorial I could find on the internet (here are couple examples[ [1], [2] of the maybe half dozen good ones found via Google search), and still no clear explanation. Although it seems it must be something fairly simple as that lack of a documented explanation implies that it's something most people would take for granted.
How do I load a custom module into Lua?
On the advice of questions like this one, I have written a module that builds a shared library with the expectation that I would be able to load it through a require call. However, when I do that I get undefined symbol errors, despite those exact symbols appearing in the list from the command nm -g mylib.so.
Those two tutorials I linked before aim to create executables that look wrappers of the *.lua file. That is, the built *.exe file should be called to run the Lua program with the custom module.
I understand that these types questions are asked here fairly frequently (as noted in this answer), but I am still at a loss. I tried some of the binding packages (Luabind and OOLua), but those didn't work out great (e.g. my earlier question--which I did ultimately figure out, sort of).
I have implemented a class in C++
I have wrapped the constructors, destructors, and functions with thunks
I have built it errorless-ly as a shared library
Yet no matter what I get undefined symbol: ... errors when I try to load it as mod = require('mylib.so'). How do I do this?
Working Example of a Library of Functions
For the record, just registering a basic function works fine. The below code, when built as libluatest.so, can be run in Lua using the commands:
> require('libluatest')
> greet()
hello world!
libluatest.cpp
extern "C"
{
#include <lualib.h>
#include <lauxlib.h>
#include <lua.h>
}
#include <iostream>
static int greet(lua_State *L)
{
std::cout << "hello world!" << std::endl;
return 0;
}
static const luaL_reg funcs[] =
{
{ "greet", greet},
{ NULL, NULL }
};
extern "C" int luaopen_libluatest(lua_State* L)
{
luaL_register(L, "libluatest", funcs);
return 0;
}
Failing Example of a Class
This is what I am stuck on currently. It doesn't seem to want to work.
myObj.h
#include <string>
class MyObj
{
private:
std::string name_;
public:
MyObj();
~MyObj();
void rename(std::string name);
};
myObj.cpp
extern "C"
{
#include <lualib.h>
#include <lauxlib.h>
#include <lua.h>
}
#include <iostream>
#include "myObj.h"
void MyObj::rename(std::string name)
{
name_ = name;
std::cout << "New name: " << name_ << std::endl;
}
extern "C"
{
// Lua "constructor"
static int lmyobj_new(lua_State* L)
{
MyObj ** udata = (MyObj **)lua_newuserdata(L, sizeof(MyObj));
*udata = new MyObj();
luaL_getmetatable(L, "MyObj");
lua_setmetatable(L, -1);
return 1;
}
// Function to check the type of an argument
MyObj * lcheck_myobj(lua_State* L, int n)
{
return *(MyObj**)luaL_checkudata(L, n, "MyObj");
}
// Lua "destructor": Free instance for garbage collection
static int lmyobj_delete(lua_State* L)
{
MyObj * obj = lcheck_myobj(L, 1);
delete obj;
return 0;
}
static int lrename(lua_State* L)
{
MyObj * obj = lcheck_myobj(L, 1);
std::string new_name = luaL_checkstring(L, 2);
obj->rename(new_name);
return 0;
}
int luaopen_libmyObj(lua_State* L)
{
luaL_Reg funcs[] =
{
{ "new", lmyobj_new }, // Constructor
{ "__gc", lmyobj_delete }, // Destructor
{ "rename", lrename }, // Setter function
{ NULL, NULL } // Terminating flag
};
luaL_register(L, "MyObj", funcs);
return 0;
}
}
Compiled into libmyObj.so using a simple CMake build with C++11 standard flags on.
Error
> require('libmyObj')
error loading module 'libmyObj' from file './libmyObj.so':
./libmyObj.so: undefined symbol: _ZN5MyObjC1Ev stack traceback: [C]:
? [C]: in function 'require' stdin:1: in main chunk [C]: ?
I am dealing with Lua 5.1 on Ubuntu 14.04.
I am wondering if it has something to do with the mix of C and C++...
It seems that you do not implement:
MyObj() ; ~MyObj();
and be careful with luaopen_* function, since module name is myObj, function name should be luaopen_libmyObj.
I am trying to define a variable from an external library in C++, Visual Studio 2010. It only works when I put it outside of the main function.
This code crashes:
#include "StdAfx.h"
#include <ogdf\basic\Graph.h>
#include <ogdf\basic\graph_generators.h>
int main()
{
ogdf::Graph g;
ogdf::randomSimpleGraph(g, 10, 20);
return 0;
}
It gives me an unhandheld exception: Access violation.
However, if it is outside main function, it works without any problem:
#include "StdAfx.h"
#include <ogdf\basic\Graph.h>
#include <ogdf\basic\graph_generators.h>
ogdf::Graph g;
int main()
{
ogdf::randomSimpleGraph(g, 10, 20);
return 0;
}
Do you have any how do I fix that? I assume, that it is caused by some kind of linking problem.
EDIT: It looks like the problem is not the initialization of the variable. It throws an exception, when the application exits.
int main()
{
ogdf::Graph g; // No problem
ogdf::randomSimpleGraph(g, 10, 20); // No problem
int i; // No problem
std::cin>>i; // No problem
return 0; // Throws an exception after read i;
}
Call stack:
The output is:
First-chance exception at 0x0126788f in graphs.exe: 0xC0000005: Access violation writing location 0x00000000.
Unhandled exception at 0x0126788f in graphs.exe: 0xC0000005: Access violation writing location 0x00000000.
Works on my machineā¢.
Esoteric errors like that are often a result of binary incompability. Basically, because of different compiler/preprocessor options, effective headers that your code and the library "see" are different.
For instance, if you have a library with following header code:
class Foo
{
#ifdef FOO_DEBUG
int debug_variable;
#endif
int variable;
};
Library function:
void bar(Foo& foo)
{
std::cout << foo.variable;
}
And client code:
Foo foo;
foo.variable = 666;
bar(foo);
If FOO_DEBUG is not in sync amongst client and the library, this will possibly crash and burn -- variable will have different expected offset.
In your case, I suspect one of the following may be true:
You have built the ogdf with different compiler than your code
If not, you ogdf and your code have different build configurations (Release vs Debug)
Both are debug, but you have defined OGDF_DEBUG (as recommended here)
You have different "Struct Member Alignment" setting