Computing › Stl › Containers › Sequences ›

Bit Vector

A bit_vector is more like a vector < bool >

View version details

Contents

Definition
Description
Bit_vector Operations
Page Comments

Key Facts

Gyroscopic Couple: The rate of change of angular momentum ( $\inline \tau$ ) = $\inline I\omega\Omega$ (In the limit).

$\inline I$ = Moment of Inertia.
$\inline \omega$ = Angular velocity
$\inline \Omega$ = Angular velocity of precession.

Definition

Bit_vector is defined in the standard header <vector>, and in the nonstandard backward-compatibility header <bvector.h>.

Description

A bit_vector is like a vector<bool>. The difference between the two is that a vector requires at least one byte per element, but a bit_vector only requires one bit per element.

Short example of using bit_vector:

bit_vector V(5);
V[0] = true;
V[1] = false;
V[2] = false;
V[3] = true;
V[4] = false;
 
for (bit_vector::iterator i = V.begin(); i < V.end(); ++i)
  cout << (*i ? '1' : '0');
cout << endl;

If you need a container for a variable number of bits or Boolean values, you can use the class bit_vector, otherwise if you need a bitfield with static size, you should use bitset.

Bit_vector Operations

Operation	Effect
c.flip()	Negates all Boolean elements (complement of all bits)
m[i].flip()	Negates the Boolean element with index i (complement of a single bit)
m[i]=`val`	Assigns val to the Boolean element with index i (assignment to a single bit)
m[i1] = m[i2]	Assigns the value of the element with index i2 to the element with index i1

References

http://www.sgi.com
Nicolai M. Josuttis: "The C++ Standard Library"

Example:

Example - implicit casts to a variable of bit_vector

Problem

This example of program illustrates examples of implicit casts done by the ostream class to a variable of bit_vector.

Workings

#include <vector>
#include <iostream>
 
using namespace std;
 
int main( )
{
   bit_vector v; 
 
   v.push_back(false);
   bit_vector::reference ref1=v.at(0);
   cout <<ref1<<endl; // ref1 implicitly cast to bool 
 
   bool b1; 
 
   // one form of an explicit cast
   b1=ref1.operator bool( );
   cout <<b1<<endl; 
 
   // another form of an explicit cast
   b1=bool(ref1);
   cout <<b1<<endl;
 
   return 0;
}

Solution

Output:

0
0
0

References

http://www.java2s.com
http://msdn.microsoft.com/en-us
Kris Jamsa, Lars Klander: "Jamsa's C/C++ Programmer's Bible"