c++ – Bitmask to Array Index – Education Career Blog

Is there a simple way to convert a bitmask in to an array index?

ie. If i’ve got an enum

a = 0x01,
b = 0x02,
c = 0x04,
d = 0x08,
e = 0x10, 

and I want to store releated data in an array, is there a simple way such that i can convert a to 0, b to 1, c to 2. etc?

Many thanks


r =   ln base 2 
and programmatically,

unsigned int v=yourEnumValue;
unsigned r = 0; 
while (v >>= 1) 

r is your answer


I’m not sure if this is what you’re asking, but why don’t you just take a 2-base log?


Log2 n?


I dont know a simple solution like you asked for, but why not just use a map instead an array?

Should work without any magic conversion.


Use a std::map:

#include <map>

std::map <my_enum, my_datatype> m;
m a  = whatever;

Leave a Comment