Question

I am tring to get table length with lua_rawlen, code like this

lua_createtable(L, 0, 0);

lua_pushstring(L, "k0");
lua_pushstring(L, "v0");
lua_settable(L, -3);
lua_pushstring(L, "k1");
lua_pushstring(L, "v1");
lua_settable(L, -3);

printf("%d\n", lua_rawlen(L, -1));

output is 0, seems it should be 2, what’s wrong with it? thanks for any advice.

Answer 1

The function lua_rawlen returns the length of a sequence without calling the optional metamethod __len. It is the equivalent of Lua function rawlen, which is the same as the # operator when there is no such __len metamethod.

Your table is not a sequence, since you only put string keys. The keys of a sequence must be consecutive integers starting from 1. Instead of "k0" and "k1" for keys, try with 1 and 2 respectively.

Example:

lua_createtable(L, 0, 0);

lua_pushstring(L, "v0");
lua_rawseti(L, -2, 1);
lua_pushstring(L, "v1");
lua_rawseti(L, -2, 2);

printf("%d\n", lua_rawlen(L, -1));