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C++ Bitset


In C++, bitset represents a fixed-sequence of some bits values by either 0 and 1. Zero represents the value as false or unset, while 1 represents the value as true or set. To create bitset of integer or a string bitset class provides constructors. The size of the bitset is determined at compile time.

In other words, bitset is used to fix all the bits to 1. If only one parameter is passed, that bit is assigned at that index.

A bitset is the array of bool. Not every Boolean value needs to be stored separately. Instead, bitset is used to optimize the space for every Boolean value it takes by 1 space or a bit. It must be noted that the space taken by bitset should be less than that or bool[n] and vector[n].

As bitset stores the same information in a compressed manner, the bitset operation is faster than that of array and vector. We can access each bit of bitset individually with the 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 for 10110, 0 are at 0th and 3rd indices whereas 1 is at 1st 2nd and 4th indices.

A bitset follows a compressive manner to store the same operation to execute faster than an array or a vector. They are easily accessible in the array by using an indexing operator[]. However, it is important to note that bitset starts its indexing in reverse direction i.e. backward. For example, 101110 is accounted to be at 0th and 3rd index while 1st and 2nd indices are accounted by 1.

To construct a bitset using integer numbers and binary string, we can do it with constructors by fixing the bitset size at the compile time thus it cannot be changed during runtime.

We can construct a bitset using integer numbers as well as a binary string via constructors which is shown below code. The size of the bitset is fixed at compile time that is, it can't be changed at runtime.

The main functions associated with bitset class are size, reset, set, and many more. Let's visualize this by the coding examples.

Syntax used in the <bitset> header file.

template <size_t N> class bitset;

Example code:

 using namespace std;
 int main ()
   bitset<20> fool(200);
   bitset<20> bark(0xfa2) ;
   bitset<20> buzz (string("0101111001"));
   cout << "fool: " << fool << '\n';
   cout << "bark: " << bark << '\n';
   cout << "buzz: " << buzz << '\n';
   return 0;



In the above code, the function bitset is imported from the header file <bitset>. The bitset functions primarily have been passed three arguments like integer, binary address, and a string of numbers. These 3 arguments are of size 2o which can be seen from the output that the integer value prints for 200. The binary value for the bitset bark has been taken as (0xfa2: some value) and the string is defined.

The output corresponding to the inputs is printed up to 20 decimal places for all the arguments.

Let us now look at the different functions associated with the bitset operations with the help of the table of reference below.

Member Types (constructors,functions, operators)Methods and Description
referenceProxy class which is used to represent reference to bit.
       constructorConstructs bitset container and initializes it for int, string etc.
       operatorsPerforms operations like AND, OR, NOT, XOR, left shift, right shift etc.
         all()Tests whether all or atleast one bit are set or not.
        count()Counts number of sets from bitset.
        none()Checks whether bits are unset or not.
        flip()Toggles single or all bitsets.
        set()Sets all bits to 1.
        reset()Sets all bits to 0.
        hash()Return hash value provided by the bitset.
        string()This converts bit objects to string objects.
        test()Checks whether Nth bit is set or not.
        ullong()Coverts bits to long or unsigned long.

Note: There are still plenty of functions present in the bitset library in the C++ language. The above are the most popular and commonly used functions.

Advantages of using bitset:

  1. bitsets are stored in a compressed manner, so the accessing is fast as compared to the arrays or vectors.
  • We can easily use bitset with constructors which make construction easier for data types like integer and binary strings.
  • The bitset size is fixed at compile-time, thus we needn't do it in the runtime which saves time.
  • The bitsets are dynamically adjustable so the array size can increase as needed.