lua_pop vs lua_remove

Question

Currently I'm building my own script VM manager class in C++. I have no problems with any of the Lua & Lua C or C++ stuff, but the one section that confuses me is when to use `lua_pop` and when to use `lua_remove`. From what I understand, `lua_pop` is to remove multiple values(on the stack) from the top down, eliminating data that is no longer needed, where as `lua_remove` is for removing a single value from any arbitrary, valid stack index (basically what the Lua manual says for both :P). But I've noticed certain segments of code scattered around the web that intermix `lua_pop` and `lua_remove`, but when I tried to use `lua_pop` instead of `lua_remove` where the call just removed the top stack element, I ran into problems. So would it be possible to get a definitive example or explanation on how and when to use these two functions correctly, as well as relative speed & efficiency for these two? I assume `lua_pop` is faster than `lua_remove`, which is one of the reasons why I want to…

Accepted Answer

A typical example of `lua_remove` is accessing tables. Snippets from Lua reference manual.

```
lua_getfield(L, LUA_GLOBALSINDEX, "t");   /* table to be indexed */
lua_getfield(L, -1, "x");        /* push result of t.x (2nd arg) */
lua_remove(L, -2);                  /* remove 't' from the stack */
```

lua_getfield pushes t[x] on the stack. You no longer need t, so you remove it.

A typical example of `lua_pop` is iterating over a table.

```
lua_pushnil(L);  /* first key */
while (lua_next(L, t) != 0) {
    /* uses 'key' (at index -2) and 'value' (at index -1) */
    /* do whatever you like with the key and the value */

lua_pop(L, 1);
}
```

After you are done with a single iteration, you need to have the key on top of the stack, so that `lua_next` knows which key/value pair comes next. You need to remove the value, which is on top of the stack.

It's not a definitive example. In Lua you do whatever works for you. Always keep in mind what's on your lua_State stack, and you'll be fine.

lua_pop vs lua_remove

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