Avoiding string duplication

[Chris Smith <space.dandy@...>]

Hi all,

I’m trying to understand a bit better the handling of strings in Lua with respect to memory allocation and what is safe or unsafe when using the C API.  The context for this is that I’m dealing with some (constant) strings that are used by both C and Lua code, and I’d like to avoid unnecessary memory allocations.

If I push a string value onto the stack (e.g. lua_getglobal(L, “my_string”) ) does Lua duplicate the string or just use a reference to the original string?

If I call lua_tostring (assuming the object is an actual string and not converted from a different type) does Lua return a pointer to the original string content or does it duplicate the string in a C-compatible manner and return a pointer to that?

Given the above and assuming that I have a Lua global string “my_string” that is constant for the lifetime of the lua_State, is the following code safe or not?

const char *str = luaL_checkstring(L, -1);
lua_pop(L, 1);
return str;

Regards,
Chris
—
Chris Smith <space.dandy@icloud.com>