C++ bitset and its application
A bitset is an array of bool but each Boolean value is not stored separately instead bitset optimizes the space such that each bool takes 1 bit space only, so space taken by bitset bs is less than that of bool bs[N] and vector bs(N). However, a limitation of bitset is, N must be known at compile time, i.e., a constant (this limitation is not there with vector and dynamic array)
As bitset stores the same information in compressed manner the operation on bitset are faster than that of array and vector. We can access each bit of bitset individually with help of array indexing operator [] that is bs[3] shows bit at index 3 of bitset bs just like a simple array. Remember bitset starts its indexing backward that is for 10110, 0 are at 0th and 3rd indices whereas 1 are at 1st 2nd and 4th indices.
We can construct a bitset using integer number as well as binary string via constructors which is shown in below code. The size of bitset is fixed at compile time that is, it can’t be changed at runtime.
The main function defined for bitset class are operator [], count, size, set, reset and many more they are explained in below code –
// C++ program to demonstrate various functionality of bitset#include <bits/stdc++.h>using namespace std; #define M 32 int main(){ // default constructor initializes with all bits 0 bitset<M> bset1; // bset2 is initialized with bits of 20 bitset<M> bset2(20); // bset3 is initialized with bits of specified binary string bitset<M> bset3(string("1100")); // cout prints exact bits representation of bitset cout << bset1 << endl; // 00000000000000000000000000000000 cout << bset2 << endl; // 00000000000000000000000000010100 cout << bset3 << endl; // 00000000000000000000000000001100 cout << endl; // declaring set8 with capacity of 8 bits bitset<8> set8; // 00000000 // setting first bit (or 6th index) set8[1] = 1; // 00000010 set8[4] = set8[1]; // 00010010 cout << set8 << endl; // count function returns number of set bits in bitset int numberof1 = set8.count(); // size function returns total number of bits in bitset // so there difference will give us number of unset(0) // bits in bitset int numberof0 = set8.size() - numberof1; cout << set8 << " has " << numberof1 << " ones and " << numberof0 << " zeros\n"; // test function return 1 if bit is set else returns 0 cout << "bool representation of " << set8 << " : "; for (int i = 0; i < set8.size(); i++) cout << set8.test(i) << " "; cout << endl; // any function returns true, if atleast 1 bit // is set if (!set8.any()) cout << "set8 has no bit set.\n"; if (!bset1.any()) cout << "bset1 has no bit set.\n"; // none function returns true, if none of the bit // is set if (!bset1.none()) cout << "bset1 has some bit set\n"; // bset.set() sets all bits cout << set8.set() << endl; // bset.set(pos, b) makes bset[pos] = b cout << set8.set(4, 0) << endl; // bset.set(pos) makes bset[pos] = 1 i.e. default // is 1 cout << set8.set(4) << endl; // reset function makes all bits 0 cout << set8.reset(2) << endl; cout << set8.reset() << endl; // flip function flips all bits i.e. 1 <-> 0 // and 0 <-> 1 cout << set8.flip(2) << endl; cout << set8.flip() << endl; // Converting decimal number to binary by using bitset int num = 100; cout << "\nDecimal number: " << num << " Binary equivalent: " << bitset<8>(num); return 0;} |
Output :
00000000000000000000000000000000 00000000000000000000000000010100 00000000000000000000000000001100 00010010 00010010 has 2 ones and 6 zeros bool representation of 00010010 : 0 1 0 0 1 0 0 0 bset1 has no bit set. 11111111 11101111 11111111 11111011 00000000 00000100 11111011 Decimal number: 100 Binary equivalent: 01100100
For bitset set, reset and flip function are defined. Set function sets (1) all bits of bitset if no argument is provided otherwise it sets the bit whose position is given as argument. In same way reset and flip also work if they are called with no argument they perform their operation on whole bitset and if some position is provided as argument then they perform operation at that position only.
For bitset all bitwise operator are overloaded that is they can be applied to bitset directly without any casting or conversion, main overloaded operator are &, |, ==, != and shifting operator <> which makes operation on bitset easy.
Use of above operator is shown in below code.
// C++ program to show applicable operator on bitset.#include <bits/stdc++.h>using namespace std; int main(){ bitset<4> bset1(9); // bset1 contains 1001 bitset<4> bset2(3); // bset2 contains 0011 // comparison operator cout << (bset1 == bset2) << endl; // false 0 cout << (bset1 != bset2) << endl; // true 1 // bitwise operation and assignment cout << (bset1 ^= bset2) << endl; // 1010 cout << (bset1 &= bset2) << endl; // 0010 cout << (bset1 |= bset2) << endl; // 0011 // left and right shifting cout << (bset1 <<= 2) << endl; // 1100 cout << (bset1 >>= 1) << endl; // 0110 // not operator cout << (~bset2) << endl; // 1100 // bitwise operator cout << (bset1 & bset2) << endl; // 0010 cout << (bset1 | bset2) << endl; // 0111 cout << (bset1 ^ bset2) << endl; // 0101} |
Output :
0 1 1010 0010 0011 1100 0110 1100 0010 0111 0101
This article is contributed by Utkarsh Trivedi. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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