Function str2num 

pub fn str2num(s: &[u8], o: &mut LuaValue) -> usize

Tries to convert the byte string s to a Lua number (integer first, then float). Writes the result to o and returns consumed_bytes + 1 on success (matching the C convention of including the null terminator in the count), or 0 on failure.

C: size_t luaO_str2num (const char *s, TValue *o)