Solved

Macro definition to write a program to test a bit.

Posted on 2003-12-09
5
272 Views
Last Modified: 2010-04-15


how do you write a macro to test whether a bit in a byte is set or not set?

For example if we want to test the fourth bit of a byte, how do we do it using the macro.

0
Comment
Question by:suresh204
  • 2
5 Comments
 
LVL 45

Expert Comment

by:sunnycoder
ID: 9909926
Hi suresh204,

#define ISSET4(X) (X)&(0x8)

Cheers!
Sunny:o)
0
 
LVL 45

Expert Comment

by:sunnycoder
ID: 9909940
a small explanation is in order ...

given any byte say
                          1 1 0 1   1 0 1 0
to determine if nth bit is 1, bitwise AND it with a number which has all bits except nth bit as 0 ... here to determine, 4th bit we use
                          0 0 0 0   1 0 0 0

                          1 1 0 1   1 0 1 0
                     &   0 0 0 0   1 0 0 0
----------------------------------------------------
                          0 0 0 0    1 0 0 0
since answer is non zero, fourth bit is set

this is also referred to as masking .. since in the constant used, all other bits are set to 0 and 0 anded with anything gives a zero, the result depends on the only set bit in the constant (mask)
0
 
LVL 8

Accepted Solution

by:
ssnkumar earned 50 total points
ID: 9910136
You can use the following macro also:
#define IS_BIT_SET(X, pos) (0x01 << (pos - 1)) & (X)

"pos" is the bit which you want to test for number "X". Count starts from right. So rightmost bit is 1, next is 2, etc.
0

Featured Post

Zoho SalesIQ

Hassle-free live chat software re-imagined for business growth. 2 users, always free.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Have you thought about creating an iPhone application (app), but didn't even know where to get started? Here's how: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Important pre-programming comments: I’ve never tri…
Summary: This tutorial covers some basics of pointer, pointer arithmetic and function pointer. What is a pointer: A pointer is a variable which holds an address. This address might be address of another variable/address of devices/address of fu…
The goal of this video is to provide viewers with basic examples to understand and use pointers in the C programming language.
The goal of this video is to provide viewers with basic examples to understand and use switch statements in the C programming language.

911 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

23 Experts available now in Live!

Get 1:1 Help Now