C++ Bitset and its Application

Last Updated : 08 Apr, 2025

In C++, the bitset is a container that represents a fixed-size sequence of bits. A bitset allows you to manipulate individual bits efficiently, making it useful in problems related to bitwise operations, such as checking flags, implementing binary representations.

Bitset is defined as the std::bitset class template inside the <bitset> header file.

Creating a Bitset

The syntax to create bitset is as follows:

C++

bitset<n> name;

where, n is the number of bits to allocate, and name is the name assigned.

Initializing

By default, when a bitset of a given size is created, all of its bits are unset i.e. 0. We can initialize it to some value simply by passing it to its constructor.

C++

//Driver Code Starts{ #include <bits/stdc++.h> using namespace std;  int main() {      //Driver Code Ends }      // Default Initialization     bitset<5> bnum(18);  //Driver Code Starts{     cout << bnum;     return 0; } //Driver Code Ends }

Here, the bitset bnum is of size 5 bits and stores the decimal value 18 in binary form.

Binary numbers are also represented as strings, so bitset also provide facility to initialize itself from the strings.

C++

//Driver Code Starts{ #include <bits/stdc++.h> using namespace std;  int main() {      //Driver Code Ends }      // Initialize bitset with value     bitset<5> bs2("10010");  //Driver Code Starts{      cout << bs2 << endl;     return 0; }  //Driver Code Ends }

The string should represent a valid binary number i.e. all characters should be 0 or 1. Otherwise, an error may occur.

Accessing Individual Bits

We access the bit at any position by using below methods:

test(pos): Returns 1 if the bit at position is 1, and 0 if it is 0.
operator[pos]: Allows direct access to a bit at a given position.

Here, pos is the position or index of the bit starting from 0. It must be in the range (0 ≤ pos ≤ size – 1), otherwise, out of bound exception is thrown.

Example:

C++

//Driver Code Starts{ #include <bits/stdc++.h> using namespace std;  int main() {      //Driver Code Ends }      // 18 = (10010)     bitset<5> bs(18);          // Check 3rd bit     cout << bs[2] << endl;          // Check 5th bit     cout << bs.test(4);  //Driver Code Starts{     return 0; } //Driver Code Ends }

Output

0 1

Setting, Resetting and Flipping

Setting means making the bit at particular position 1 and resetting means making it 0. These operations can be done using set() and reset() function. The flip() function can be used to set the bit if it’s not set and unset if it is set.

Example:

C++

//Driver Code Starts{ #include <bits/stdc++.h> using namespace std;  int main() { //Driver Code Ends }      bitset<5> bs(18);          // Set 1st bit     bs.set(0);     cout << bs << endl;          // Reset 2nd bit      bs.reset(1);     cout << bs << endl;          // Flip 5th bit     bs.flip(4);  //Driver Code Starts{     cout << bs;     return 0; } //Driver Code Ends }

Output

10011 10001 00001

Bitset Operators

Bitset objects can work with all the bitwise operators to provide seamless replacement integration in the code.

Operator	Operation
&	Bitwise AND
\|	Bitwise OR
^	Bitwise XOR
>>=	Binary Right shift and assign
<<=	Binary Left shift and assign
&=	Assign the value of bitwise AND to the first bitset.
\|=	Assign the value of bitwise OR to the first bitset.
^=	Assign the value of bitwise XOR to the first bitset.
~	Bitwise NOT

Example:

C++

//Driver Code Starts{ #include <bits/stdc++.h> using namespace std;  int main() { //Driver Code Ends }       // 18 = (10010)     bitset<5> bs1(18);          // 5 = (00101)     bitset<5> bs2(5);          // AND Operator      cout << (bs1 & bs2) << endl;          // OR Operator     cout << (bs1 | bs2) << endl;          // XOR operator     cout << (bs1 ^ bs2);  //Driver Code Starts{     return 0; }  //Driver Code Ends }

Output

00000 10111 10111

Explanation: In the above example, we perform AND, OR and XOR operator on bitsets:

bs1 & bs2: Return (0 0 0 0).
bs1 | bs2: Print (1 0 1 1 1).
bs1 ^ bs2: Print (1 0 1 1 1).

Other Basic Operations

Find the Size of the Bitset
Convert Bitset to Unsigned Long Long
Convert Bitset to Unsigned Long
Check if at least One Bit is Set in Bitset
Check if all Bits are Unset
Check if all Bits are Set

Internal Working

In C++, bitset is implemented using an array or similar structure to store its bits. When you perform operations like set(), reset(), or flip(), they directly modify the bits in the internal array. The size of the bitset is fixed at compile-time, and it cannot be dynamically resized.

Why Bitset is Preferred

Bitsets are a preferred choice for bitwise operations and binary data handling due to the following reasons:

Bitsets are memory-efficient, as each bit occupies just one bit, making them ideal for large binary datasets.
Bitsets enable efficient bit manipulation, providing a better alternative to integers or arrays of booleans for handling large bit sequences.
The bitset provides an easy way to work with bits, eliminating the need for writing complicated custom functions.
Since the size of a bitset is determined at compile time, it helps with consistent memory usage and performance, making it well-suited for applications where efficiency is important.
Using bitsets clearly signals bit-level manipulation, which improves code clarity and reduces errors.

Difference between std::bitset and std::vector<bool> and an array of bool

Vector of bool and array of bool can also be implemented to store a sequence of boolean values like bitset but there are some differences between each implementation:

Parameter	bitset	vector of bool	array of bool
Definition	A class template consisting of a sequence of bits stored such that each bit occupies 1 bit of memory.	A variation of vectors of C++ STL in which each element is of size 1 bit and is of type bool	A fixed size contiguous collection of bool data elements.
Size	Fixed Size.	Dynamic Size.	Fixed Size.
Memory	A single element occupies 1 bit of memory.	A single element occupies 1 bit of memory.	A single element occupies 1 byte of memory.
Speed	Same	Same	Faster

All Member Functions

Here’s the list of all member functions of std::bitset:

Function	Description
set()	Set the bit value at the given index to 1.
reset()	Set the bit value at a given index to 0.
flip()	Flip the bit value at the given index.
count()	Count the number of set bits.
test()	Returns the boolean value at the given index.
any()	Checks if any bit is set.
none()	Checks if all bits are unset.
all()	Check if all bit is set.
size()	Returns the size of the bitset.
to_string()	Converts bitset to string.
to_ulong()	Converts bitset to unsigned long.
to_ullong()	Converts bitset to unsigned long long.

Bits manipulation (Important tactics)

Utkarsh Trivedi

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Article Tags :

Practice Tags :

C++ Bitset and its Application

Creating a Bitset

Initializing

Accessing Individual Bits

Setting, Resetting and Flipping

Bitset Operators

Other Basic Operations

Internal Working

Why Bitset is Preferred

Difference between std::bitset and std::vector<bool> and an array of bool

All Member Functions

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