Bitwise operations | And | Which situation is true

问题:

I show my question by an example :

    int a = 1 << 0; // = 1
    int flag = 1;
    bool b = flag & a; // = 1 < In c++ this line has no error but in c# error is like this :

Cannot be applied to operands of type 'bool' and 'int'

1. When b variable is true and when b variable is false in c#?

2. How fix the error?

3. When does c++ recognize that b variable is true? The other side should be (flag & a) != 0 or (flag & a) == 1 or something else?

回答1:

In C# you write it like so:

bool b = (flag & a) != 0;

You can't assign an int to a bool in C#, like you can in C++.

(In C++ the compiler generates code that effectively does the same as the code above, although most C++ compilers will generate a warning if you just try to assign an int to a bool.)

Also see the Visual C++ warning C4800, which tells you to write it this way in C++ too.

回答2:

In C/C++, false is 0, and true is non-zero (!0). C++ treats every value as boolean (as in, any value can be tested for its truth-iness).

In C#, the types are better enforced, so you can't simply test a number for truthiness.

You'd have to equate the resulting expression to something:

bool b = (flag & a) != 0;