_Find_first() function in C++ bitset with Examples

The _Find_first() is a built-in function in C++ Biteset class which returns an integer that refers the position of first set bit in bitset. If there isn’t any set bit, _Find_first() will return the size of the bitset.

Syntax:

iterator bitset._Find_first()
           or
int bitset._Find_first()

Parameters: The function accepts no parameter.

Return Value: The function returns an integer which refers to the position of first set bit in bitset. If there isn’t any set bit, _Find_first() will return the size of the bitset.

Below is the illustration of the above function:

// C++ program for illustration
// of _Find_first() function

#include <bits/stdc++.h>
using namespace std;

#define M 32

int main()
{
    // default constructor initializes with all bits 0
    bitset<M> bset;
    bitset<M> bset1;

    // 00000000000000000000000000100000
    bset[5] = 1;

    // 00000000000000000000010000100000
    bset[10] = 1;

    // function returns the first set bit in Bitset
    cout << "position of first set bit in bset\n";
    cout << bset._Find_first() << "\n";

    // function returns bset1.size()
    // when no bit is set in bitset.
    cout << "position of first set bit in bset1\n";
    cout << bset1._Find_first() << "\n";

    return 0;
}

Output:

position of first set bit in bset
5
position of first set bit in bset1
32

Reference: https://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-3.4/bitset-source.html

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