Re: append table on c api

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.