Last Updated: 2024-11-23

What is the advantage?

• each digit in octal represents 3 bits.
• it's a nice way to make binary representations human readable without making them difficult to convert back to underlying binary (as would happen, e.g. with decimal representation compare decimal st_mode (stat data type) of 33188 in decimal to 0100644 in octal. Given that we know the last 9 bits in octal are the permission bits, we can read off the permissions as 644

re conversion:

just replace the octdigits with 3 bits binary strings (0=000, 1=001, 2=010, 3=011, 4=100, 5=101, 6=110, 7=111) and finally remove all leading zeros to the left and when you do binary to octal just add no to 2 zeros to the left until the length is divisible by 3 and than translate block of 3 bits.

How to know when a number is represented as such?

• a leading 0 - e.g. instead of let x = 52; you have let x = 052;. The leading 0 is informative since it is always superfluous.
• no number will be higher than 7.
• the context is usually C / unix, some low level language

Resources

• https://stackoverflow.com/questions/35375084/c-unix-how-to-extract-the-bits-from-st-mode
• https://www.quora.com/What-are-the-benefits-and-disadvantages-of-the-octal-counting-system-that-the-decimal-system-doesn%E2%80%99t-have