how can you check an individual binary digit in c++

Question

I apologize for being vague, but our teacher specifically told us to do so if we ask questions

I have 9 flags I want to store as an integer.
ie, 0b111111111 would be all of them tripped.

Right now I have an if statement adding to the int if it's tripped. ie.

if (flag0=="tripped" && flag0=="hasn't been tripped before") flagInt += 1;

if (flag1=="tripped" && flag1=="hasn't been tripped before") flagInt += 2;

if (flag2=="tripped" && flag2=="hasn't been tripped before") flagInt += 4;

and so on,

I'm having difficulty writing the code to check if a flag has been tripped or not. How could I do this?

edit: I've considered converting the integer to a string of it's binary representation, so I could just chck with brackets, but I have to do this for quite a bit of data, and that would make it too slow

Use binary `&` operator and a mask (e.g. 0b00000010 for flag1) to check if single bits are set (result is > 0 in case of a matching bit). — πάντα ῥεῖ, Sep 08 '13 at 00:57

score 3 · Answer 1 · answered Sep 08 '13 at 00:58

3

To get bit n state (returns bit n as 0 or 1):

(value>>n) & 1

To set bit n state (flag is 0 or 1):

value = (value & ~(1 << n)) | (flag << n)

answered Sep 08 '13 at 00:58

mvp

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bool play::used(int flag,int a){ int b = flag & a; if (flag == a) return true; return false; } thanks a lot, this is what I used. – d0m1n1c Sep 08 '13 at 01:18

how can you check an individual binary digit in c++

1 Answers1