C/C++ How to get least significant bit

[KAZZQE]

Good day.

I need to get the least significant bit of an unsigned char in C/C++.
can you give me an idea, how to solve this?
a C solution is what i prefer, but a C++ solution is also good.(:

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[codestation]

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foo & 1

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[KAZZQE]

thx.(:
you're the best.

and how about the most significant bit?

[Salmon]

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(i >> sizeof(i)) & 1

There is probably a better way to do it.

[codestation]

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(i >> sizeof(i)) & 1

There is probably a better way to do it.

Not exactly as sizeof of an [unsigned] char is always 1 so you are shifting only one bit.

A correct answer would be:

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foo >> sizeof(foo) * CHAR_BIT - 1 & 1;

[Salmon]

Woops. Thanks for picking up on that mistake.

[KAZZQE]

ok. thanks for your answers.(:

i used the code of @codestation, but made it shorter..
would it have the same effect?

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msb = (foo >> 7) & 1;

[m0skit0]

Nope because you're not taking into account the size of foo (that's why sizeof() is used...). Using sizeof() is way better because foo can be any size. Using 7 is less portable. Also using literals is a bad programming practice.

Keep in mind that sizeof() (IIRC) is a compile-time function, and thus you don't have any speed penalty using it.

Resuming: always use sizeof()

[KAZZQE]

but..
..sizeof(an unsigned char) is 1.
..CHAR_BIT is 8.

1 * 8 - 1 is 7?

the unsigned char cannot change its own type and CHAR_BIT has a constant value..
or did i understand wrong..?

[codestation]

but..
..sizeof(an unsigned char) is 1.

In C99 this is guaranteed.

..CHAR_BIT is 8.

Nope, you can find DSP where CHAR_BIT is 16 or even 32.

I used sizeof on my example (even with a char variable), because it can be used without modifications for other data types like short and int without guessing the the size value. For example you can find cases where sizeof(int) == 1 . Like m0skit0 said already, try to avoid literals on your code so it can be more portable.