How can I store a series of bits in a variable using C language

Question

How can I store this series of bits "000001111110001" (15bits) in a variable using C language.

I tried to store it into unsigned int:

unsigned int key=000001111110001;

but it doesn't, so please help me.

Answer 1

Usually, the bits are broken down into 4 bits at a time, and then converted to hexadecimal representation:

unsigned int key = 0x03F1;

You can choose to break the bits down into 3 bits at a time and use octal representation ( 01761 ), or use regular decimal representation ( 1009 ).

If you want to use bits, you can build it up yourself like this:

unsigned int key = (1<<9)|(1<<8)|(1<<7)|(1<<6)|(1<<5)|(1<<4)|(1<<0);

Or, perhaps slightly more mnemonic:

#define b4(x) \
    ((((0##x >> 9) & 01) << 3) | \
     (((0##x >> 6) & 01) << 2) | \
     (((0##x >> 3) & 01) << 1) | \
     (((0##x >> 0) & 01) << 0))
#define b8(x1, x0) ((b4(x1) << 4) | b4(x0))
#define b16(x3, x2, x1, x0) ((b8(x3, x2) << 8) | b8(x1, x0))

unsigned int key = b16(0000,0011,1111,0001);

The macro b4(x) expects x to be 4 binary digits as input, and converts it into a 12 bit octal number (that is 3 bits is used to represent a single binary digit). Then, it converts that 12 bit octal number into a true 4 bit number. b8(a,b) , and b16(a,b,c,d) extend on b4(x) .

Fancier macro tricks may help you do it in an even more automated way. See for example P99 .

Answer 2

If your compiler supports it (see FDinoff comment), you can represent an integer value in binary format if you precede it with a 0b :

unsigned int x = 0b000001111110001;

Some alternatives:

• 000001111110001 is 1009 for ten-fingered humans, so just represent this value:

unsigned int x = 1009;

• 000001111110001 is 3F1 in hexadecimal, use 0x prefix:

unsigned int x = 0x3F1;

• If you want things more complicated, represent it in octal form, use 0 prefix:

unsigned int x = 01761;

The thing is that no matter how you represent 1009 (000001111110001, 3F1, 1761), always the same bits will go in those sizeof(unsigned int) bytes (at least for the same endianness).