Thread: Printing certain bits

You aren't really clear as to what it is you want to print. I assume you want to print something different if a specific bit is set.

Code:

if( ISSET( value, bit ) )
    printf( "Bit %d is set\n.", bit );

If that's the case, take a look at this: FAQ > Bit shifting and bitwise operations - Cprogramming.com


Quzah.

Originally Posted by r_james14

Hi There,

I have a hexadecimal number anything between 0 and ffff, what is the simplist way of printing certain bits. Reason im asking is the hexideciamal is broken down into its individual bits and each bit has its own meaning, like bit 1 if high means power present low means no power etc.

What i want to end up with is

printf("Power Present %x, (First bit of the number));
printf("Switched On %x,(Second bit of the number));

etc lol

thanks in advance

Code:

printf("Power is %s\n", (val & 1) ? "on" : "off");
printf("Switch is %s\n", (val & 2) ? "on" : "off");
printf("Fan is %s\n", (val & 4) ? "on" : "off");
//etc.

The trick is ... condition ? true : false ... acts like an inline if() statement.

The values of each bit are powers of 2 ... 1, 2, 4, 8, 16, 32, 64, 128, etc.

It's equivalent to...

Code:

printf( "Power  is ");
if ((val & 1) > 0 )
  printf("on\n");
else
 printf("off\n");

Just in more compact syntax.

Although I know my powers of two up to 262144, I prefer to use hexadecimal to represent bit masks in something like the above:

Code:

printf("Engine is %s\n", (val & 0x08) ? "on" : "off");
printf("Navigation system is %s\n", (val & 0x10) ? "on" : "off");
printf("Thrusters are %s\n", (val & 0x20) ? "on" : "off");

A nicer way that enables you to somewhat number the bits is to use a rightshift:

Code:

printf("Communication systems are %s\n", ((val >> 6) & 1) ? "on" : "off");
printf("Weapons are %s\n", ((val >> 7) & 1) ? "on" : "off");
printf("World domination is %s\n", ((val >> 8) & 1) ? "on" : "off");

(Note the 6, 7, and 8, the values from 0 to 15 correspond to the various bits starting from 0=rightmost)