lua_newuserdata简单使用

void *lua_newuserdata (lua_State *L, size_t size);

lua_newuserdata 函数按照指定的大小分配一块内存，将对应的 userdatum放到栈内，
并返回内存块的地址。

一个简单的调用lua_newuserdata 分配空间的例子：

LuaTestDll.h

extern "C"
{
#include "lua/lua.h"
#include "lua/lualib.h"
#include "lua/lauxlib.h"
#include "lua/luaconf.h"


LUATESTDLL_API int luaopen_mylib(lua_State *L);

};

LuaTestDll.cpp

#include "LuaTestDll.h"

typedef struct NumArray
{
	int size;
	double values[1];
}NumArray;

static int newarray(lua_State *L)
{
	int n = luaL_checkint(L,1);

	//由于原始的结构中已经包含了一个元素的空间，所以我们从n 中减去 1
	size_t nbytes = sizeof(NumArray) + (n-1)*sizeof(double);	
	//调用lua_newuserdata分配指定的大小空间，并压入栈中作为返回值
	NumArray *a = (NumArray*)lua_newuserdata(L,nbytes);
	a->size = n;

	//分配的内存已经在栈中
	return 1;
}

static int setarray(lua_State *L)
{
	NumArray *a = (NumArray*)lua_touserdata(L,1);
	int index = luaL_checkint(L,2);
	double value = luaL_checknumber(L,3);

	luaL_argcheck(L,a != NULL,1,"array expected");
	luaL_argcheck(L,1<=index && index <=a->size,2,"index out of range");

	//设置数组值
	a->values[index-1] = value;

	return 0;
}

static int getarray (lua_State *L)
{
	NumArray *a = (NumArray*)lua_touserdata(L,1);
	int index = luaL_checkint(L,2);

	luaL_argcheck(L,a != NULL,1,"array expected");
	luaL_argcheck(L,1<=index && index <=a->size,2,"index out of range");

	//返回对应值
	lua_pushnumber(L,a->values[index-1]);

	return 1;
}

static int getsize(lua_State *L)
{
	NumArray *a = (NumArray*)lua_touserdata(L,1);

	//判断参数正确性
	luaL_argcheck(L,a != NULL,1,"array expected");

	//返回数组大小
	lua_pushnumber(L,a->size);

	return 1;
}

static const struct luaL_reg arraylib[] = 
{
	{"new",newarray},
	{"set",setarray},
	{"get",getarray},
	{"size",getsize},
	{NULL,NULL}
};

int luaopen_mylib(lua_State *L)
{
	luaL_openlib(L,"array",arraylib,0);
	return 1;
}

Test.lua

func =  package.loadlib("LuaTestDll.dll","luaopen_mylib");
func();		--导出函数
a = array.new(1000);	--分配1000个空间大小
print(a);	--> userdata: 0x8064d48 
print(array.size(a));	--> 1000
for i=1,1000 do
	array.set(a,i,1/i);
end
print(array.get(a,10));	--> 0.1