How to read Lua table return value from C++

Question

I have a Lua function that returns table (contains set of strings) the function run fine using this code:

lua_pushstring (lua, "funcname");  
lua_gettable   (lua, LUA_GLOBALSINDEX);
lua_pushstring(lua, "someparam");
lua_pcall (lua, 1, 1, 0);

the function returns a table. How do I read it's contents from my C++ code?

score 5 · Accepted Answer · answered Oct 19 '10 at 17:37

5

If you are asking how to traverse the resulting table, you need lua_next (the link also contains an example). As egarcia said, if lua_pcall returns 0, the table the function returned can be found on top of the stack.

answered Oct 19 '10 at 17:37

sbk

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`lua_next()` will enumerate all of contents of the table, however, it may be easier to directly access the table if the index is known. `lua_gettable()`, `lua_getfield()`, `lua_rawget()`, or `lua_rawgeti()` can all access the contents of a table if an index is known. – gwell Oct 19 '10 at 19:40
@gwell: true, but given that OP used `lua_gettable` in his sample, I assumed he already knows about some of those at least. – sbk Oct 20 '10 at 12:18

score 1 · Answer 2 · answered Oct 19 '10 at 15:52

If the function doesn't throw any errors, then lua_pcall will:

Remove the parameters from the stack
Push the result to the stack

This means that, if your function doesn't throw any errors, you can use lua_setfield right away - lua_pcall will work just like lua_call:

lua_pushstring (lua, "funcname");  
lua_gettable   (lua, LUA_GLOBALSINDEX);
lua_pushstring(lua, "someparam");
lua_pcall (lua, 1, 1, 0);
lua_setfield(L, LUA_GLOBALSINDEX, "a");        /* set global 'a' */

would be the equivalent of:

a = funcname(someparam)

Assigning the table to a global is not exactly the same as reading its contents. — gwell, Oct 19 '10 at 19:06

How to read Lua table return value from C++

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