struct somedata {
int a;
int b;
};
somedata *tdata = (somedata*)lua_newuserdata(L,sizeof(somedata));
tdata->a = 10;
lua_setglobal(L,"somedata");
print(somedata.a)
LUA: lua_setglobal
Author
i want to add a global variable with userdata in it.
i made a struct:
and i wanted to add it by calling:
but when i call:
See here for an example of userdata. With some meta table hackery you could make it so that instead of the example (array.size(a)) you could use (a:size()). Then take the basic approach and make it work for what you are trying.
Lua will not allow you to do what you are trying, not without a bit more work anyway [smile]
Lua will not allow you to do what you are trying, not without a bit more work anyway [smile]
Author
what did i do wrong?
like in the example:
- i called lua_newuserdata() with luastate and size of my struct.
- i set a property.
- i made it a global variable.
so what would i need to do?
like in the example:
- i called lua_newuserdata() with luastate and size of my struct.
- i set a property.
- i made it a global variable.
so what would i need to do?
You didn't expose the variable to Lua. Lua just takes a userdata and stores it, it doesn't know what it represents. All it known is its size. Lua cannot determine the names of the members of the struct - even if it wanted to. It is a good idea that it doesn't do this - it allows you to implement private variables.
However, the alternative is to not use a userdata at all and instead create a regular lua table. I'm haven't done this in C++ before so I'll leave you with this page, which hopefully describes what you need to know.
However, the alternative is to not use a userdata at all and instead create a regular lua table. I'm haven't done this in C++ before so I'll leave you with this page, which hopefully describes what you need to know.
Quote:Original post by madmaurice
and what about light user data?
Almost the same as a regular userdata, except you only pass Lua a pointer.
If you explain what you are trying to do then maybe we could make a suggestion. You hardly are trying to expose a 2 integer struct called "somedata" to Lua!
What I do for my game is have an array (std::vector actually) of objects I want to expose to Lua. I provide an interface for getting and setting the values. I use simple functions to do this. Example:
struct Example{ int a,b; };std::vector<Example> examples;int create( lua_State *L ){ Example example; data.b = lua_tointeger(L,-1); lua_pop(L,1); data.a = lua_tointeger(L,-1); lua_pop(L,1); examples.push_back(example); // return index lua_pushinteger(L,examples.size()-1); return 1;}// and a similar function for bint setA( lua_State *L ){ int a = lua_tointeger(L,-1); lua_pop(L,1); int index = lua_tointeger(L,-1); lua_pop(L,1); if( index >= 0 && index < examples.size() ) { examples[index].a = a; } else { // handle error } return 0;}int getA( lua_State *L ){ int index = lua_tointeger(L,-1); lua_pop(L,1); if( index >= 0 && index < examples.size() ) { lua_pushinteger(L,examples[index].a); return 1; } else { // handle error } return 0;}Then I write a lua script like so(assuming all the above functions are in a namespace/table "example"):
Example = {}function Example.new(a,b) local e = {} setmetatable(e,{__index=Example}) e.index = example.create(a,b) return eendfunction Example.getA() return example.getA(self.index)endfunction Example.setA(a) example.setA(self.index,a)endThis may not be the best way, but it has advantages for me. Firstly, the data remains in a contiguous block in C++, so I can store objects by value in a vector, rather than messing around with pointers. Also, I prefer writing table manipulation code in lua. I could change the C++ functions to parse lua tables but I find that awkward to write.
Obviously I just wrote that example off the top of my head - it has neither been compiled nor tested. In addition, it lacks error handling.
Author
i don't want to create an instance i just want to read out a struct instance when it was giving as a parameter or as a global.
oh sry didn't checked your post.
oh sry didn't checked your post.
Author
ok now i made a class for that but any error occurs while linking -.-
damn! so much work and no result.
damn! so much work and no result.
Quote:Original post by madmaurice
ok now i made a class for that but any error occurs while linking -.-
damn! so much work and no result.
If you need help, post the errors and code.
This topic is closed to new replies.
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