# std::bitset<N>::bitset

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< cpp‎ | utility‎ | bitset

| (1) |
bitset(); |  | (until C++11)
constexpr bitset() noexcept; |  | (since C++11)
| (2) |
bitset( unsigned long val ); |  | (until C++11)
constexpr bitset( unsigned long long val ) noexcept; |  | (since C++11)
| (3) |
template< class CharT, class Traits, class Alloc > explicit bitset( const std::basic_string<CharT,Traits,Alloc>& str, typename std::basic_string<CharT,Traits,Alloc>::size_type pos = 0, typename std::basic_string<CharT,Traits,Alloc>::size_type n = std::basic_string<CharT,Traits,Alloc>::npos); |  | (until C++11)
template< class CharT, class Traits, class Alloc > explicit bitset( const std::basic_string<CharT,Traits,Alloc>& str, typename std::basic_string<CharT,Traits,Alloc>::size_type pos = 0, typename std::basic_string<CharT,Traits,Alloc>::size_type n = std::basic_string<CharT,Traits,Alloc>::npos, CharT zero = CharT('0'), CharT one = CharT('1')); |  | (since C++11)
template< class CharT > explicit bitset( const CharT* str, typename std::basic_string<CharT>::size_type n = std::basic_string<CharT>::npos, CharT zero = CharT('0'), CharT one = CharT('1')); | (4) | (since C++11)

Constructs a new bitset from one of several optional data sources:

1) Default constructor. Constructs a bitset with all bits set to zero.
2) Constructs a bitset, initializing the first (rightmost, least significant) `M` bit positions to the corresponding bit values of `val`, where `M` is the smaller of the number of bits in an `unsigned long long` and the number of bits `N` in the bitset being constructed. If M is less than N (the bitset is longer than 32 (until C++11)64 (since C++11) bits, for typical implementations of unsigned long (since C++11)long), the remaining bit positions are initialized to zeroes.
3) Constructs a bitset using the characters in the std::basic_string `str`. An optional starting position `pos` and length `n` can be provided, as well as characters denoting alternate values for set (`one`) and unset (`zero`) bits. `Traits::eq()` is used to compare the character values.
The effective length of the initializing string is min(`n`, `str.size() - pos`).
If `pos > str.size()`, this constructor throws std::out_of_range. If any characters examined in `str` are not `zero` or `one`, it throws std::invalid_argument.
4) Similar to (3), but uses a `CharT*` instead of a std::basic_string. Equivalent to bitset(n == basic_string<CharT>::npos ? basic_string<CharT>(str) : basic_string<CharT>(str, n), 0, n, zero, one)

### Parameters

val | - | number used to initialize the bitset
str | - | string used to initialize the bitset
pos | - | a starting offset into `str`
n | - | number of characters to use from `str`
one | - | alternate character for set bits in `str`
zero | - | alternate character for unset bits in `str`

### Exceptions

3) std::out_of_range if pos > str.size(), std::invalid_argument if any character is not one or zero
4) std::invalid_argument if any character is not one or zero

### Example

Run this code

    #include <bitset>
    #include <string>
    #include <iostream>
    #include <climits>

    int main()
    {
        // empty constructor
        std::bitset<8> b1; // [0,0,0,0,0,0,0,0]

        // unsigned long long constructor
        std::bitset<8> b2(42);          // [0,0,1,0,1,0,1,0]
        std::bitset<70> bl(ULLONG_MAX); // [0,0,0,0,0,0,1,1,1,...,1,1,1] in C++11
        std::bitset<8> bs(0xfff0);      // [1,1,1,1,0,0,0,0]

        // string constructor
        std::string bit_string = "110010";
        std::bitset<8> b3(bit_string);       // [0,0,1,1,0,0,1,0]
        std::bitset<8> b4(bit_string, 2);    // [0,0,0,0,0,0,1,0]
        std::bitset<8> b5(bit_string, 2, 3); // [0,0,0,0,0,0,0,1]

        // string constructor using custom zero/one digits
        std::string alpha_bit_string = "aBaaBBaB";
        std::bitset<8> b6(alpha_bit_string, 0, alpha_bit_string.size(),
                          'a', 'B');         // [0,1,0,0,1,1,0,1]

        // char* constructor using custom digits
        std::bitset<8> b7("XXXXYYYY", 8, 'X', 'Y'); // [0,0,0,0,1,1,1,1]

        std::cout << b1 << '\n' << b2 << '\n' << bl << '\n' << bs << '\n'
                  << b3 << '\n' << b4 << '\n' << b5 << '\n' << b6 << '\n'
                  << b7 << '\n';
    }

Possible output:

    00000000
    00101010
    0000001111111111111111111111111111111111111111111111111111111111111111
    11110000
    00110010
    00000010
    00000001
    01001101
    00001111

### See also

set | sets bits to true or given value (public member function)
reset | sets bits to false (public member function)

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