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

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bitset::operator==bitset::operator!=

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bitset::operator&=bitset::operator|=bitset::operator^=bitset::operator~

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

Accesses the bit at positionpos.

1) Returns the value of the bit.

2) Returns an object of typestd::bitset::reference that allows modification of the value.

Ifpos< size() isfalse, the behavior is undefined.

(until C++26)

Ifpos< size() isfalse:

If the implementation ishardened, acontract violation occurs. Moreover, if the contract-violation handler returns under “observe” evaluation semantic, the behavior is undefined.
If the implementation is not hardened, the behavior is undefined.

(since C++26)

[edit]Parameters

pos

position of the bit to return

[edit]Return value

1) The value of the requested bit.

2) An object of typestd::bitset::reference, which allows writing to the requested bit.

[edit]Exceptions

Throws nothing.

[edit]Example

Run this code

#include <bitset>#include <cstddef>#include <iostream> 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]: 0b1[1]: 1b1[2]: 0b1[3]: 1b1[4]: 0b1[5]: 1b1[6]: 0b1[7]: 0After setting bit 0, b1 holds 00101011

[edit]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 atpos was equivalent to that of`test(pos)`, but`test()` may throw exceptions	avoids mentioning`test()`