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always "attempt to call a nil value"......when pcall in lua api

Started by skybreaker Apr 11, 2006 at 9:02 AM 2 replies 14.1k views

Original Post

Apr 11, 2006 at 9:02 AM

Hello : I'm a new user of lua,I'm tring to call a simple function in file. in my application:


lua_State* luaVM =  lua_open();
	if (NULL == luaVM)
	{
		MyEngineERR("luaL_error Initializing lua\n");
		return -1;
	}
	if (luaL_loadfile(luaVM,filename)!=0) 
	{
		MyEngineERR((LPSTR)lua_tostring(luaVM, -1));
		lua_pop(luaVM, 1); 
		lua_close(luaVM);
		return -1;
	}
// loading is succesful
        const char name[]="add";
	lua_getglobal(luaVM,name);
//when I remove this line pcall succesful,or I will get a "attempt to call a nil value"
	if(lua_pcall(luaVM,0,0,NULL)!=0)
	{
		MyEngineERR((LPSTR)lua_tostring(luaVM, -1));//
		lua_pop(luaVM, 1);
                lua_close(luaVM);
 	}

in the scripts file:


function add()
a=1+1
end

Am I do somethin wrong?and I'm using lua 5.1.Thanks for any suggestions.

Zorbfish

Apr 11, 2006 at 10:24 AM

You have loaded your Lua file but not executed it. When you call luaL_loadfile Lua only compiles the file and places it on the stack. Do a lua_pcall before trying to call add and it will put your add function into the globals table.

With the code you have now Lua cannot find add because it was never placed in the globals table (that is why you get the nil message).

Derakon

Apr 11, 2006 at 7:47 PM

As Zorbfish says. The reason for this is that files are just functions. lua_loadfile will put the "function of the file" on the top of the Lua stack for you, but it won't execute that function until you do lua_pcall. When you do execute lua_pcall, the function is executed, and returns a function called "new". That function is added to the globals table, which is why you can access it later by using lua_getglobal.

skybreaker

Apr 11, 2006 at 8:04 PM

It works haha...thanks a lot thanks thanks thanks....

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