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Common usage of bitset in c++

Popularity：295 ℃/2025-02-19 09:08:15

In C++bitsetIt is a template class for handling fixed-size bit sequences, providing efficient bit operation functions. Here is a detailed introduction to its key features:

1. Declaration and Initialization

  • Header file: Need to include<bitset>。
  • statement：bitset<N>Indicates a containingNBinary set of bits (Nis a compile-time constant).
    bitset<8> b1; // Default initialization, all bits are 0
 bitset<4> b2(5); // Initialize with integer: 0101
 bitset<4> b3("1010"); // Initialize with string: 1010
 bitset<4> b4(b3); // Copy construct

2. Initialization rules

  • Integral initialization: High truncation, low truncation.
    bitset<3> b(10); // The binary of 10 is 1010 → truncated to 010 (value is 2)
  • String initialization：
    • Strings can only contain'0'and'1'。
    • By default, from stringLeft end (high position)Start parsing.
    bitset<4> b("1010"); // High → Low : 1 0 1 0 → Decimal 10
 bitset<4> b("101010", 2, 4); // Take 4 bits from index 2: "1010" → The value is 10

3. Common operations

  • bit access：

    • []Operator: Accessed through index (from right to left, 0 is the lowest bit).
    • test(pos): Check whether the specified bit is 1, and an exception is thrown out of bounds.
    bitset<4> b("1010");
 bool bit0 = b[0]; // 0 → lowest bit
 bool bit3 = b[3]; // 1 → highest bit

  • Modify bit：

    • set(pos, val): Set a certain bit (default 1).
    • reset(pos): Clear a bit (set to 0).
    • flip(pos): Flip a certain position.
    (0);       // 1010 → 1011
(3);     // 1011 → 0011
(1);      // 0011 → 0001

  • Statistics and judgments：

    • count(): Returns the number of 1.
    • any()/none()/all(): Determine whether there is/no/all are 1.
    if (()) cout << "At least 1 bit is 1";

4. Bit operation

  • support&、|、^、~、<<、>>Equal operator (the length must be the same):
    bitset<4> a("1010"), b("1100");
auto c = a & b;     // 1000
auto d = a << 1;    // 0100

5. Type conversion

  • to_ulong()/to_ullong(): Convert to an unsigned integer (possibly overflowed).
  • to_string(): Convert to a string to specify padding characters.
    bitset<4> b(10);
string s = b.to_string(); // "1010"

6. Application scenarios

  • Bit flag management: such as permission control, status marking.
  • Bitmask operation: Quickly filter or modify specific bits.
  • Data compression: efficiently store boolean values.

Sample code

#include <bitset>
 #include <iostream>
 using namespace std;

 int main() {
     bitset<8> b1(42); // 0010101010
     bitset<8> b2("10101010"); // 10101010
     cout << b1 << endl; // Output 0010101010
     (0); // becomes 00101011
     (); // becomes 0101010101
     cout << (b1 & b2) << endl; // 00000001
     cout << b1.to_ulong() << endl; // 43
     return 0;
 }

Things to note

  • Visit across the border：test(pos)Will check for cross-border,[]Won't.
  • performance:Efficient bit operation, suitable for intensive computing.
  • String order: The first character of the string corresponds to the high bit.

bitsetIt is a powerful tool for processing binary data. Combined with clear bit sequence rules and rich interfaces, it can significantly simplify bit-level operation code.

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