I'm currently learning using LUA in C++ code. And I came to a point where I cannot figure out how to use C++ function in LUA's code.
I want to create simple function in c++ and then use it in LUA.
My approach is as follows (taken from some tutorials):
In main.cpp:
void write(const char* str) {
std::cout<<str<<std::endl;
}
static int l_write(lua_State* L) {
const char* str = lua_tostring(L, 1); // get function argument
write(str); // calling C++ function with this argument...
return 0; // nothing to return!
}
int main(){
lua_State* L = luaL_newstate();
luaL_openlibs(L); // load default Lua libs
if (luaL_loadfile(L, "test.lua")) {
std::cout<<"Error loading script"<<std::endl;
}
lua_pushcfunction(L, l_write);
lua_setglobal(L, "write"); // this is how function will be named in Lua
lua_pcall(L, 0, 0, 0); // run script
}
and in test.lua I've got:
write("Hello, world!")
write("The square root of 2 is "..math.sqrt(2))
x = 42
write("We can use variables too, x = "..x)
The problem appears in the very beginning of this code: I cannot even a load script luaL_loadfile(L, "test.lua") returns value 7 (which is as I checked NIME_AGAIN 7 /* temporarily out of resources */).
Everything else works just fine do provided I don't use my custom c++ functions. I can load values from LUAs file normally, can execute function ect.
I suppose that LUA after reading file already compiles it and then finds out name of function that does not exist, namely "write" and returns error in case of reading this file, is it possible? And if so how to resolve this problem, and how to use this feature correctly?
Mhm, guys. It is strange but I did lua_pop(L, 1) once, run and then delete it and now its working just fine O.o
Related
The problem is, a "require" keyword clears all global variables defined in the same file.
I am working on a project in c++. I use lua 5.3. The lua scripting style is:
1 all lua codes contains 1 common library file, and several small files each acting as a function.
2 when program start, the lua common library is compiled and executed, leave its global variables in the lua state. Then the small files are compiled not executed.
3 when program come to some point, relevant small lua file will be called(just as I say, every small file is a function). The global functions and variables defined in the common library will be used in the small lua file. That's why I compile and execute the common library when program start.
4 I'm very sure I only use 1 lua_State.
It worked fine, until I decide to split common library to multiple files, And use "require" in the main file. When program start, the main file will be compiled and executed.
Not a single code changed, just add come "require". Strange thing happened: All global variables and global functions are missing. When global function is called in small lua file, a "called a nil value" error raises.
I then make a experiment, I delete all "require" lines in the main library file, and it turns out that the global functions defined in the main library worked very well. I then require a empty file "simple.lua", the global functions defined in the main library was missing, cannot be called from the small lua file.
How to explain this? How can a "require" keyword clears all global variables defined in the same file?
in lua library:
require("simple")
function foo()
return 1+1
end
in lua small file
return foo()
result: attempt to call a nil value (global 'foo')
after delete "require", lua library:
function foo()
return 1+1
end
result: no error happens, 2 is returned
the c++ side code:
lua common library compile and excute:
int code = luaL_loadbuffer(L, s, strlen(s), "commonlib");
if(code != 0) {
std::string error = lua_tostring(L, -1);
lua_pop(L, 1);
return error;
}
code = lua_pcall(L, 0, 0, 0);
if(code > 0)
{
std::string ret = lua_tostring(L, -1);
lua_pop(L, 1);
return ret;
}
else
return ""; //empty string means no error
lua small function file compile:
int code = luaL_loadbuffer(L, s, strlen(s), "RULE1");
if(code != 0) {
std::string error = lua_tostring(L, -1);
lua_pop(L, 1);
return error;
}
else
{
return ""; //return empty means no error
}
The L in both code is the same lua state (or it won't work when "require" is removed). After compile, the small file function at the stack top is saved in global register with a reference variable "ref".
When call lua small file, the ref is pushed in the stack, a lua_pcall is used, nothing special.
Resolved the problem by myself.
Because of a duplicated copy/paste, the lua vm is created the second time afterwards. It's rather confusing because if there is no "require", everything is alright. It is a total coincidence.
All I learnt from this is: always double check the copy/paste code.
I spent few hours trying to make it work without success. I have a C++ program with function exposed to Lua script. Lua script uses it like this:
setData('type', {a=1, b=2, c=3})
So first argument is string and second is table.
My current and best version of C++ setData function looks like this:
string sType;
map<string, uint8_t> mOptions;
int nArgs = lua_gettop(i_pState);
if (nArgs == 2)
{
if (lua_isstring(i_pState, 1) != 0)
sType = lua_tostring(i_pState, 1);
if (lua_istable(i_pState, 2) != 0)
{
lua_pushnil(i_pState);
while(lua_next(i_pState, 2))
{
uint8_t nValue = uint8_t(lua_tonumber(i_pState, -1));
string sKey = lua_tostring(i_pState, -2);
mOptions[sKey] = nValue;
lua_pop(i_pState, 1);
}
lua_pop(i_pState, 1);
}
}
return 0;
It works fine but causes "program.exe has triggered a breakpoint" error afterwards at the end when lua_close() function called.
What is wrong with this code?
UPD1. I'm not getting error without handling second argument.
UPD2. My code behaves very strangely. I think it could be issue of mixing extern "C" and C++ code.
UPD3. Turns out this is heap corruption. I can't understand where is cause. Probably this is not related to lua at all.
Finally! Recompilation of Lua code as C++ code didn't work (positive thing is I don't have to worry about extern "C" anymore). But I found two redundant lua_pop() calls. I removed them and now it works fine.
I didn't expect Lua to be so dangerous!
Good afternoon,
I am working on a LUA/C++ application, from which i need lua to be able to call other lua code recursively, e.g: C++ calls lua function, lua function calls another lua function from another string that is loaded using a registered C function that runs at the start of the first lua function;
here are the steps i am following:
lua_State* state = luaL_newstate();
luaL_openlibs(state);
lua_register(state, "secondLua", secondLua);
lua_getfield( _luaState, LUA_GLOBALSINDEX, "init" );
lua_pcall( _luaState, 0, 0, 0 );
int secondLua(lua_State* state){
char* myString[128] = "function init2()\n io.write(\"hello\")\n end";
luaL_loadstring(pLuaState, myString);
lua_getfield(pLuaState,LUA_GLOBALSINDEX, "init2"); // function init2 declared on myString
lua_pcall(pLuaState, 0, LUA_MULTRET, 0);
//getting "attempt to call a nil value" here
return 0;
}
Any help is appreciated, and second, i would like to know if there is a way i can name the second function "init" as well as the first one;
PS: I am using C++14 and lua 5.1 on LUAJIT, and i cant use lua's dofile;
lua_loadstring() compiles supplied source and puts Lua chunk on stack. It won't execute it though, so init2() still not defined when you expect that.
Replace lua_loadstring() with luaL_dostring() to actually run that chunk and define new lua functions. Or call lua_pcall() right after lua_loadstring(). Actually, luaL_dostring() does exactly that - lua_loadstring() followed by lua_pcall().
I am trying to call lua functions in cocos2d-x. However when I try to pass some variables to lua functions. My program stopped at lua_call().
My function:
const char* getData::callLuaFunction(const char* luaFileName,const char* functionName){
lua_State* ls = CCLuaEngine::defaultEngine()->getLuaStack()->getLuaState();
std::string filefullpath = CCFileUtils::sharedFileUtils()->fullPathForFilename(luaFileName);
const char* pfilefullpath = filefullpath.c_str();
int isOpen = luaL_dofile(ls, pfilefullpath);
if(isOpen!=0){
CCLOG("Open Lua Error: %i", isOpen);
return NULL;
}
lua_getglobal(ls, functionName);
lua_pushstring(ls, "einverne");
lua_pushnumber(ls, 2);
lua_pushboolean(ls, true);
lua_call(ls, 3, 1);
const char* iResult = lua_tostring(ls, -1);
return iResult;
}
Function in lua file:
function luaLogString(_logStr,_logNum,_logBool)
print("Lua string from C：",_logStr,_logNum,_logBool)
return "call lua function OK"
end
Edit:
I have found lua_call is not protected. lua_pcall function is safer. And after I changed to lua_pcall. Errors show that attempt to call global '聽聽聽聽print' (a nil value)
Actually I found the problem.
I delete four space before print function in lua file and everything is OK.
And I suggest newbie to use lua_pcall rather than lua_call. Because if there is an error when calling lua_call , this function will call exit(EXIT_FAILURE) and shutdown host program without giving an error message.
The difference between lua_pcall and lua_call
English version
Chinese version
I'm implementing Lua as a script language into a Windows application. Due to the application's structure, printout isn't using streamed io, such as stdout and stderror.
I have managed to override the Lua print to fit into my structure...
lua_register(L,"print", cs_print);
...but how do I override all error an debug printouts without using streams? I need to handle this in a function (similar to print).
The only place where Lua writes to stderr is in the panic function that luaL_newstate installs. If you're embedding Lua into your application, make sure you start Lua from a protected call and no panic will ever occur. See http://www.lua.org/source/5.2/lua.c.html#main for ideas.
After a lot of Google I came up with this solution to fetch compiler and runtime error messages as well to redirect the standar Lua print function.
I use C++ Builder but I think it can be useful for anyone looking for the same answer.
The script is running in a TScriptLua object instance and to map a Lua state against the correct script instance, I use a std::map list to look up the object pointer.
// list for mapping Lua state with object pointers.
static std::map<lua_State*,TScriptLua*> LuaObjMap;
Next is an inline function to get the object pointer from a Lua state pointer.
extern "C" {
// Inline to map Lua state pointer to object pointer
static inline TScriptLua* GetScriptObject(lua_State* L) {
return LuaObjMap.find(L)->second;
}
This function will replace the standard Lua print function. The object pointer (f) has a member function in its base class called Out() that will output a char buffer in the associated window control.
// New Lua print function
static int cs_print (lua_State *L) {
// Map Lua state to object
TScriptLua* f = GetScriptObject(L);
if (f) {
int count = lua_gettop(L);
for (int i=1; i <= count; ++i) {
const char *str = lua_tostring(L, i); // Get string
size_t len = lua_rawlen(L,i); // Get string length
// Output string.
f->Out(str,len);
}
}
return 0;
}
This is my error print routine that will display the compiler/runtime error. As for the Lua print function, the f->Out is used again to print the error message.
// Error print routine
static int cs_error(lua_State *L, char *msg) {
// Map Lua state to object
TScriptLua* f = GetScriptObject(L);
// Get error message
AnsiString m = String(msg) + " " + String(lua_tostring(L, -1));
// "print" error message
f->Out(m.c_str(),m.Length());
// Clenaup Lua stack
lua_pop(L, 1);
return 0;
}
} // <--- End extern C
Here is the actual load and run member. After the new Lua state has been created it is associated with this object in the mapping list. Then it loads the script from a Rich edit control with luaL_loadbuffer(), checks for compiler errors and runs the compiled script with lua_pcall().
void __fastcall TScriptLua::Compile(void) {
// Create new Lua state
lua_State *L = luaL_newstate();
// Store mapping Lua state --> object
LuaObjMap.insert( std::pair<lua_State*,TScriptLua*>(L,this) );
// Override Lua Print
lua_register(L,"print", cs_print);
// Load and compile script
AnsiString script(Frame->Script_RichEdit->Text);
if (luaL_loadbuffer(L,script.c_str(),script.Length(),AnsiString(Name).c_str()) == 0) {
if (lua_pcall(L, 0, 0, 0)) // Run loaded Lua script
cs_error(L, "Runtime error: "); // Print runtime error
} else {
cs_error(L, "Compiler error: "); // Print compiler error
}
// Close Lua state
lua_close(L);
// Remove Lua --> object mapping
LuaObjMap.erase( LuaObjMap.find(L) );
}
This isn't my final solution, but it does the trick so far. I think the best thing is to write stream handling into the TScriptLua object so I can register it directly into Lua.