Function lua_tointeger 

pub unsafe fn lua_tointeger(L: *mut lua_State, idx: c_int) -> lua_Integer

Attempts to convert the value at the given index to an integer, and returns it.

This function operates in a similar way as lua_tonumber, but it has the final result floored to an integer. While it will convert a string into a number on the stack, it will not modify the stack value into an integer.