bitwise operations in c++, how to actually use it?

Question

I understand

  11001110
& 10011000
= 10001000

but I want to test it myself

so I declare unsigned char and print it out, but it just gives me blank.

unsigned char result;
result= 11001110 & 10011000;

cout<<result;

Also tested with unsigned int, but it gives me 0, which is not what I expected

You're currently defining decimal numbers. See [this question](http://stackoverflow.com/q/2611764/311966) for how to specify a binary literal — simonc, May 14 '13 at 16:04
that's because those numbers are decimal, not binary read [this thread][1] about how to use binary in C++ [1]: http://stackoverflow.com/questions/2611764/can-i-use-a-binary-literal-in-c-or-c — Sergi0, May 14 '13 at 16:05
@Sergi0, actually [this](http://stackoverflow.com/questions/537303/binary-literals/538101#538101) thread and answer, as C++11 is already here — Lol4t0, May 14 '13 at 16:13

score 3 · Accepted Answer · edited May 14 '13 at 16:06

3

11001110 and 10011000 aren't binary numbers (at least in the compiler's mind).

Binary 11001110 is 206, and 10011000 is 152, so you actually want (I think):

result = 206 & 152;

or use a std::bitset and then print result as a binary.

edited May 14 '13 at 16:06

taocp

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answered May 14 '13 at 16:03

Luchian Grigore

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Or wait until next year and (hopefully) write `0b11001110`. – Mike Seymour May 14 '13 at 16:09
@MikeSeymour, Too bad we won't be able to say `0b1011_1000_0001` AFAIK, though. – chris May 14 '13 at 16:11
@chris `BOOST_BINARY(1011 1000 0001)` – PiotrNycz May 14 '13 at 16:45
@PiotrNycz, Interesting. Hopefully they figure out the digit separators problem, though. – chris May 14 '13 at 16:47

score 3 · Answer 2 · answered May 14 '13 at 16:07

3

You might want to consider using hex for testing

int a = 0xCE;    // 11001110
int b = 0x98;    // 10011000

int result = a & b;

cout << hex << result << endl;

or write a function to convert result to binary.

answered May 14 '13 at 16:07

gongzhitaao

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score 1 · Answer 3 · answered May 14 '13 at 16:10

1

In c++ you have to use hex to express bits number. Because 11001110 is 0XCE and 10011000 is 0X98

unsigned char b1 = 0XCE;
unsigned char b2 = 0X98;
unsigned char b = b1 & B2;

answered May 14 '13 at 16:10

diwatu

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You don't have to use hex. Decimal and octal work fine as well. Hex is just nicer sometimes. – chris May 14 '13 at 16:13
in standard c++, no octal data type you can use. if you use decimal(i know you mean integer here), it is hard to understand its bytes. – diwatu May 14 '13 at 16:15
@Giswin C++ has octal literals, just like it has hexadecimal literals. – juanchopanza May 14 '13 at 16:28

score 0 · Answer 4 · answered May 14 '13 at 16:05

0

11001110 in binary is NOT the same number in decimal.

Since c++ does not have a binary specifier (but has hex and octal), you need to use something like an online converter.

Get an online binary to decimal converter, convert 11001110 to decimal, 10011000 to decimal, do the & operation, Then convert the result from decimal back to binary.

answered May 14 '13 at 16:05

Boyko Perfanov

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Or you could just convert it in your head, or even the Windows calculator (if you use Windows). Or use `std::bitset`. – chris May 14 '13 at 16:07
Fun exercise: write it yourself in `c++`. It's not hard. – BoBTFish May 14 '13 at 16:09

score 0 · Answer 5 · answered May 14 '13 at 16:07

If you write 11001110, you'll get a decimal, not a binary number, like Luchian pointed out.

To get a binary, you have to write 0b11001110... The prefix 0b means in gcc, clang and tcc, you are using binary system.

I don't know, what the Visual C++ Compiler will do with this prefix.

bitwise operations in c++, how to actually use it?

5 Answers5