Solved

How to initialize bitwise parameter ?

Posted on 2014-01-03
4
297 Views
Last Modified: 2014-01-03
struct ParameterDef
{
   ....
   /* bit 0 indicates if the parameter is special or not.  It it's special read remaining bit(s)
       to find the specialty. */
   /* bit 0 -   special 1, not special 0
       bit 1 -   map modbus register value to whole number
       bits 2 - 15    -   reserved for future use
  */    
   unsigned short special_param_bits;
}

Open in new window


There is array of above structure.  

How to initialize special_param_bits variable with symbols instead of numbers ?
For special array entires, I want to indicate that the paramter is special and what specialty it has.  i.e. SPECIAL & MAP_MODBUS_REG
0
Comment
Question by:naseeam
  • 2
  • 2
4 Comments
 
LVL 86

Assisted Solution

by:jkr
jkr earned 200 total points
ID: 39754594
You already have it, the bitwise AND (&) will help you here

#define SPECIAL 1 // LSB == bit 0, or '1 << 0'
#define MAP_MODBUS_REG (1 << 5) // assuming it is bit 5
ParameterDef pd;

pd.special_param_bits = SPECIAL & MAP_MODBUS_REG;

Open in new window

0
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 300 total points
ID: 39754601
Use the bitwise operators with the appropriate flags. In this case, to set it you will use bitwise OR if you have multiple things to set.

e.g.

const short FLAG_SPECIAL =    0x80000000;
const short FLAG_MAP_MODBUS = 0x40000000;

struct ParameterDef instance;
instance.special_param_bits = FLAG_SPECIAL | FLAG_MAP_MODBUS;

Open in new window


Each flag needs to be a power of 2 in its value, since each flag's value represents a bit position within the short. Speaking in bits, your flags look like this:

const short FLAG_SPECIAL =    1000 0000 0000 0000;
const short FLAG_MAP_MODBUS = 0100 0000 0000 0000;

Open in new window

0
 
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 39754620
For correctness, jkr's suggestion of bitwise AND is actually incorrect. AND is for querying if a bit has been set; OR is used for setting the bit. In other words, 1 & 0 == 0 whereas 1 | 0 == 1.
0
 
LVL 86

Expert Comment

by:jkr
ID: 39755587
*Argh*, it of course has to be 'OR', this is embarassing ;o)
0

Featured Post

Announcing the Most Valuable Experts of 2016

MVEs are more concerned with the satisfaction of those they help than with the considerable points they can earn. They are the types of people you feel privileged to call colleagues. Join us in honoring this amazing group of Experts.

Question has a verified solution.

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

Suggested Solutions

Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
This article is meant to give a basic understanding of how to use R Sweave as a way to merge LaTeX and R code seamlessly into one presentable document.
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
Viewers will learn how to properly install Eclipse with the necessary JDK, and will take a look at an introductory Java program. Download Eclipse installation zip file: Extract files from zip file: Download and install JDK 8: Open Eclipse and …

839 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