A bitset is an array of bools but each boolean value is not stored in a separate byte instead, bitset optimizes the space such that each boolean value takes 1-bit space only, so space taken by bitset is less than that of an array of bool or vector of bool.
A limitation of the bitset is that size must be known at compile time i.e. size of the bitset is fixed.
std::bitset is the class template for bitset that is defined inside <bitset> header file so we need to include the header file before using bitset in our program.
Syntax:
bitset<size> variable_name(initialization);
We can initialize bitset in three ways :
1. Uninitialized: All the bits will be set to zero.
bitset<size> variable_name;
2. Initialization with decimal integer: Bitset will represent the given decimal number in binary form.
bitset<size> variable_name(DECIMAL_NUMBER);
3. Initialization with binary string: Bitset will represent the given binary string.
bitset<size> variable_name(string("BINARY_STRING");
bitset<size> variable_name("BINARY_STRING");
Example:
C++
// C++ program to demonstrate the bitset #include <bitset>#include <iostream>using namespace std;int main(){ // declaring an uninitialized bitset object bitset<8> uninitializedBitset; // initialization with decimal number bitset<8> decimalBitset(15); // initialization with binary string bitset<8> stringBitset(string("1111")); cout << "Uninitialized bitset: " << uninitializedBitset << endl; cout << "Initialized with decimal: " << decimalBitset << endl; cout << "Initialized with string: " << stringBitset << endl; return 0;} |
Uninitialized bitset: 00000000 Initialized with decimal: 00001111 Initialized with string: 00001111
std::bitset Member Functions
std::bitset class contains some useful member functions to work on the bitset objects. Here is the list of some member functions of std::bitset:
|
Function Name |
Function Description |
|---|---|
| Set the bit value at the given index to 1. | |
|
reset() |
Set the bit value at a given index to 0. |
| Flip the bit value at the given index. | |
| Count the number of set bits. | |
|
test() |
Returns the boolean value at the given index. |
| Checks if any bit is set. | |
| Checks if none bit is set. | |
| Check if all bit is set. | |
|
size() |
Returns the size of the bitset. |
|
to_string() |
Converts bitset to std::string. |
|
to_ulong() |
Converts bitset to unsigned long. |
|
to_ullong() |
Converts bitset to unsigned long long. |
Example:
C++
// C++ program to demonstrate the// use of std::bitset member// functions#include <bitset>#include <iostream>using namespace std;int main(){ // declaring index variable int index = 0; // declaring few bitset objects bitset<4> allSet("1111"), allUnset; cout << "any() value: " << boolalpha << allSet.any() << endl; cout << "all() value: " << allSet.all() << endl; cout << "none() value: " << allSet.none() << endl; cout << "test() at index 0: " << noboolalpha << allSet.test(index) << endl; cout << "size() value: " << allSet.size() << endl; cout << "Value of allUnset on before using set(): " << allUnset << endl; allUnset.set(index); cout << "Value of allUnset on after using set(): " << allUnset << endl; cout << "Value of allSet on before using reset(): " << allSet << endl; allSet.reset(index); cout << "Value of allSet on after using reset(): " << allSet << endl; // declaring an empty string string bitString; // using to_string() method to assign value to empty // string bitString = allSet.to_string(); cout << "bitString: " << bitString << endl; cout << "Unsigned Long value: " << allSet.to_ulong(); return 0;} |
any() value: true all() value: true none() value: false test() at index 0: 1 size() value: 4 Value of allUnset on before using set(): 0000 Value of allUnset on after using set(): 0001 Value of allSet on before using reset(): 1111 Value of allSet on after using reset(): 1110 bitString: 1110 Unsigned Long value: 14
Note: boolalpha is used to print “true” and “false” instead of 1 or 0 for boolean values and noboolalpha for opposite.
std::bitset Operators
Some of the basic operators are overloaded to work with bitset objects. Following is the list of those operators:
|
Operator |
Operation |
|---|---|
|
[] |
Access operator |
|
& |
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++
// C++ program to show the different operator functions on// bitset#include <bitset>#include <iostream>using namespace std;int main(){ bitset<4> bitset1("1001"), bitset2("1010"); bitset<4> result; cout << "Bitset1: " << bitset1 << "\nBitset2: " << bitset2 << endl; cout << "Accessing bit value at index 1 of bitset1: " << bitset1[1] << endl; // bitwise AND cout << "Bitwise AND using &: " << (result = bitset1 & bitset2) << endl; cout << "Bitwise AND using &=: " << (bitset1 &= bitset2) << endl; // bitwise OR bitset1 = 9; // 9 = 1001 cout << "Bitwise OR using |: " << (result = bitset1 | bitset2) << endl; cout << "Bitwise OR using |=: " << (bitset1 |= bitset2) << endl; // bitwise NOT cout << "Bitwise NOT: " << (result = ~bitset1) << endl; // bitwise XOR bitset1 = 9; cout << "Bitwise XOR: " << (bitset1 ^= bitset2) << endl; bitset1 = 9; cout << "Binary leftshift on bitwise1: " << (bitset1 <<= 1) << endl; bitset1 = 9; cout << "Binary rightshift on bitwise1: " << (bitset1 >>= 1) << endl; return 0;} |
Output
Bitset1: 1001 Bitset2: 1010 Accessing bit value at index 1 of bitset1: 0 Bitwise AND using &: 1000 Bitwise AND using &=: 1000 Bitwise OR using |: 1011 Bitwise OR using |=: 1011 Bitwise NOT: 0100 Bitwise XOR: 0011 Binary leftshift on bitwise1: 0010 Binary rightshift on bitwise1: 0100
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 |
This article is contributed by Utkarsh Trivedi. Please write comments if you find anything incorrect, or if you want to share more information about the topic discussed above.
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