Bit Flags Issue

This is a discussion on Bit Flags Issue within the C++ Programming forums, part of the General Programming Boards category; After finishing reading a tutorial on bit flags, i decided to do some practicing. Here's what I came up with: ...

  1. #1
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    Bit Flags Issue

    After finishing reading a tutorial on bit flags, i decided to do some practicing.

    Here's what I came up with:

    Code:
    #include <iostream>
    #include <string>
    
    using namespace std;
    
    enum PersonSettings
    {
        Works = 1,
        Studies = 2,
        HasKids = 4,
        LivesAlone = 8
    };
    
    class Person
    {
        public:
            Person(string n, PersonSettings s);
            void printSettings();
        private:
            string name;
            PersonSettings settings;
    };
    
    Person::Person(string n, PersonSettings s) : name(n), settings(s)
    {
    
    }
    
    void Person::printSettings()
    {
        cout<<"WORKS? ";
        if(settings & Works) cout<<"YES"; else cout<<"NO";
        cout<<endl;
    
        cout<<"STUDIES? ";
        if(settings & Studies) cout<<"YES"; else cout<<"NO";
        cout<<endl;
    
        cout<<"HAS KIDS? ";
        if(settings & HasKids) cout<<"YES"; else cout<<"NO";
        cout<<endl;
    
        cout<<"LIVES ALONE? ";
        if(settings & LivesAlone) cout<<"YES"; else cout<<"NO";
        cout<<endl;
    }
    
    int main()
    {
        Person someone("Jack",LivesAlone | HasKids);
        someone.printSettings();
        cout<<endl;
    }
    It works well ONLY if set one bit flag on the constructor, if i try to set more than one bit flag (like in the code above) it displays the following error report:

    error: invalid conversion from `int' to `PersonSettings'|
    line of error:
    Person someone("Jack",LivesAlone | HasKids);
    Oh, and BTW, is this a correct usage of bit flags?

  2. #2
    and the hat of wrongness Salem's Avatar
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    Well the combined result isn't a valid enum value.

    An enum is a rather more distinct type in C++ than it is in C.
    Incompatibilities Between ISO C and ISO C++
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    still, it's not clear to me why the OR bit operator doesnt work as it should.

    I'll even write a simpler code that makes the compiler reports the same error message:

    Code:
    #include <iostream>
    #include <stdlib.h>
    
    int main()
    {
    
          enum mySettings
          {
               opt1 = 1,
               opt2 = 2,
               opt3 = 4,
               opt4 = 8
          };
    
          mySettings options;
          options = opt3 | opt4;
    
          cout<<hex<<options<<endl;
    
          system("PAUSE");
          return 0;
    }

  4. #4
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    Quote Originally Posted by dhuan View Post
    still, it's not clear to me why the OR bit operator doesnt work as it should.
    As already indicated by Salem, the OR is executed correctly, the result is simply not a valid enum value, so that you cannot assign the result., hence the error. In your example, 4 | 8 = 12. There is no enum member with a value of 12, hence the compiler bails.
    iMalc: Your compiler doesn't accept misspellings and bad syntax, so why should we?
    justin777: I have no idea what you are talking about sorry, I use a laptop and there is no ascii eject or something

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