Re: append table on c api
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- Subject: Re: append table on c api
- From: Sean Conner <sean@...>
- Date: 2012年12月11日 14:41:41 -0500
It was thus said that the Great Philipp Kraus once stated:
> Hello,
>
> I generate a table with
>
> lua_newtable
> lua_pushxxx()
> lua_setfield(L, -2, "mykey")
> lua_setglobal
>
>
> This works at the moment, I try to create a table like
> { "key1" : { "subkey" : 123 }, "key2" : { "subkey" : 456 } }
>
> but I don't know how to append some new elements like
> { "key1" : { "subkey" : 123 }, "key2" : { "subkey" : 456, "newkey" : 789} }
>
> I get the first table put it on top of the stack, than I use getfield to
> check if the field exists, if it is nil, I pop the nil value and run newtable,
> but if the value with the key exists (it must be a table), than the table is on top,
> but how can I add on a table a new key-value pair? So I would like to
> overwrite an existing key or I would like to append a new one.
> Must I put all element on the stack top?
>
> in short I try to solve this:
>
> if table exists
> push it on the stack
> if key exists
> push it on the stack and replace value
> else
> push a new key-value pair on the stack
> add it to table
> move table from stack and append data
> else
> create table
> create key-value pair and put it into table
>
> Can me anybody explain how the append works?
Assuming the following:
t = { key1 = { subkey = 123 } , key2 = { subkey = 456 , newkey = 789 } }
my_append(t)
Then:
int my_append(lua_State *L)
{
luaL_checktype(L,1,LUA_TTABLE); /* t -- t */ /* make sure we only have a table */
lua_getfield(L,-1,"key2"); /* t -- t key2 */ /* get key2 */
if (lua_isnil(L,-1))
{
lua_pop(L,1); /* t nil -- t */ /* pop nil from stack */
lua_createtable(L,0,0); /* t -- t t */ /* create a table */
lua_pushvalue(L,-1); /* t t -- t t t */ /* dup it */
lua_setfield(L,-3,"key2"); /* t t t -- t t */ /* and set it as key2 in the passed in table */
}
else
luaL_checktype(L,-1,LUA_TTABLE); /* t t -- t t */ /* make sure it's a table */
lua_pushinteger(L,314); /* t t -- t t 314 */ /* set anewkey to 314 */
lua_setfield(L,-2,"anewerkey"); /* t t 314 -- t t */
lua_pop(L,1); /* t t -- t */
return 1; /* return passed in table */
}
Untested code, but the above should set key2.anewerkey to 314 in the passed
in table (and create key2 if it doesn't exist). The first comments is a
stack diagram (a concept from Forth)---the top of the stack is always on the
right, and the diagram shows the stack before and after the function
(stack-before-call '--' stack-after-call), which should make the logic a bit
more clearer.
-spc