为 Bitset 赋值

Question

I'm curious to know why the following code is working, According to bitset template class. you can assign a value to bitset (int or binary representation as string) by constructor but not after that. But here you can see that explicit assign of a integer works fine.

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

int main()
{
    bitset<8> b(string("101"));
    cout << b.to_ullong()<<"\n";
    b= 145;
    cout << b<<"\n";
    return 0;
}

this question also might be relevant. How to assign bitset value from a string after initializaion

Answer 1

Bitset's non-string constructors are implicit .

If they were declared as explicit you would indeed have to write

b = bitset<8>(145);

Answer 2

What might seem confusing is the fact that std::bitset does not explicitly define operator= . Compiler will, however, generate one (see this question). You can actually check that using cppinsight . This means that, in combination with the implicit constructor mentioned in the accepted answer, your code works. You can see the constructor call and subsequent assignment in the cppinsight example.