What Is The Meaning Of 0b00 And 0b11 In C/C++? - Stack Overflow

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Learn more about Labs What is the meaning of 0b00 and 0b11 in C/C++? [duplicate] Ask Question Asked 4 years, 10 months ago Modified 4 years, 10 months ago Viewed 13k times 0 This question already has answers here: Can I use a binary literal in C or C++? (25 answers) Closed 4 years ago.

I have a small question I hope there is a simple answer there. When programming an Arduino in C/C++ the line "DDRB |= 0b00101000;" occurs. While I know DDRB is the Data Direction Register for port B and the meaning of the numbers after "0b00" (which are the slots 13 to 9), I still don't really know what "0b00" means. In definitions I only read it means HIGH (while 0b11 means LOW) but what does that mean? Full code:

#include <avr/io.h> #include <util/delay.h> int main (void) { float seconds = 0.5; int time = 1000 * seconds; DDRB |= 0b00101000; while (1) { PORTB |= 0b00001000; _delay_ms(time); PORTB &= 0b11110111; PORTB |= 0b00100000; _delay_ms(time); PORTB &= 0b11011111; } return 0; }

• c++
• arduino

Share Improve this question Follow edited Jan 13, 2020 at 13:17 Lali asked Jan 13, 2020 at 13:08 LaliLali 1311 gold badge11 silver badge44 bronze badges 6

• 3 A binary number? – Evg Commented Jan 13, 2020 at 13:10
• 2 Are you asking about the 0b syntax? Or Arduino specific part? – Yksisarvinen Commented Jan 13, 2020 at 13:10
• The b prefix specifies a binary literal, as opposed to a decimal literal. In this case 0b00101000 == 40, but since you are using it to check bits, it is more readable to express in binary. – Cory Kramer Commented Jan 13, 2020 at 13:10
• Please note that you are likely writing C++, not C, if you are working with Arduino. – walnut Commented Jan 13, 2020 at 13:10
• Thank you for clarification walnut. And thank you CoryKramer I think I'm starting to get it. – Lali Commented Jan 13, 2020 at 13:17

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3 Answers 3

Sorted by: Reset to default Highest score (default) Trending (recent votes count more) Date modified (newest first) Date created (oldest first) 7

0b means that a number in binary representation is expected.

For Data direction registers, setting the bits to 1 will make the respective lines outputs, and setting to 0 will make them inputs.

The DDRB |= 0b00101000 will do a binary OR operation between the current value of the bits in DDRB with the mask.

This will result in DDRB = 0b××1×1xxx, so that means DDRB will keep the value for lines 7 and 6. This operation basically sets lines 5 and 3 as Output and leaves the rest as they were.

Share Improve this answer Follow edited Jan 13, 2020 at 13:52 Ted Lyngmo 115k77 gold badges7979 silver badges128128 bronze badges answered Jan 13, 2020 at 13:37 Vlad StoianVlad Stoian 8622 bronze badges Add a comment | 1

As you tag your question "Arduino", you might be interested that besides the standard c++ 0b... notation the IDE also provides all 8-bit combinations of binary numbers in B00101000 format, with and without leading zeros.

Usually, hex notation (0x28 in your example) is even easier readable, IMO

Share Improve this answer Follow answered Jan 13, 2020 at 13:29 datafiddlerdatafiddler 1,83533 gold badges1919 silver badges3030 bronze badges Add a comment | 0

The line

DDRB |= 0b00101000

basically does a bitwise OR with the mask 0b00101000 and reassigns the results to DDRB.

0b indicates that whatever comes next should be interpreted as binary, so it's easier to see which bits you are masking.

The code is just setting the bits masked as 1 to HIGH and leaving the others unchanged.

Share Improve this answer Follow answered Jan 13, 2020 at 13:14 user2261062user2261062 Add a comment |

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