# std::bitset<N>::operator[]

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< cpp‎ | utility‎ | bitset

| (1) |
bool operator[]( std::size_t pos ) const; |  | (until C++11)
constexpr bool operator[]( std::size_t pos ) const; |  | (since C++11)
| (2) |
reference operator[]( std::size_t pos ); |  | (until C++23)
constexpr reference operator[]( std::size_t pos ); |  | (since C++23)

Accesses the bit at position pos. The first version returns the value of the bit, the second version returns an object of type std::bitset::reference that allows modification of the value.

Unlike test(), does not throw exceptions: the behavior is undefined if pos is out of bounds.

### Parameters

pos | - | position of the bit to return

### Return value

1) The value of the requested bit.
2) An object of type std::bitset::reference, which allows writing to the requested bit.

### Exceptions

None

### Example

Run this code

    #include <iostream>
    #include <bitset>

    int main()
    {
        std::bitset<8> b1{0b00101010}; // binary literal for 42

        for (std::size_t i = 0; i < b1.size(); ++i)
            std::cout << "b1[" << i << "]: " << b1[i] << '\n';
        b1[0] = true; // modifies the first bit through bitset::reference

        std::cout << "After setting bit 0, b1 holds " << b1 << '\n';
    }

Output:

    b1[0]: 0
    b1[1]: 1
    b1[2]: 0
    b1[3]: 1
    b1[4]: 0
    b1[5]: 1
    b1[6]: 0
    b1[7]: 0
    After setting bit 0, b1 holds 00101011

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 11 | C++98 | 1. the description was missing in the C++ standard 2. there was only the non-const overload | 1. description added 2. added the const overload
LWG 907 | C++98 | the behavior of reading the bit at pos was equivalent to that of `test(pos)`, but `test()` may throw exceptions | avoids mentioning `test()`

### See also

test | accesses specific bit (public member function)

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