How to assign multiple enum value to same enum variable in c++?

Question

For example，we initialize an instance of enum.

enum weekdays {Saturday, Sunday, Tuesday,Wednesday, Thursday, Friday} weekend;

and can we make weekend assigned both Saturday and sunday？

Do you understand that enumerator values are just numbers? Which by default start at 0 and increment by 1? — MSalters, Oct 25 '17 at 12:59
@Sean - That doesn't assign both values to `weekend`. It will not be equal to either. — StoryTeller - Unslander Monica, Oct 25 '17 at 13:14
@StoryTeller - I'm aware of that. I'm trying to provide some pointers about what he'd need to change in his example (ie the values of the days)/ — Sean, Oct 25 '17 at 13:16
@Sean - I know *you* know. But giving a hint like that is only likely to confuse the OP. He doesn't seem to grasp basics here. So my comment is actually geared more towards *him*. — StoryTeller - Unslander Monica, Oct 25 '17 at 13:19
@StoryTeller thank you,my english is not good.But i already search lots of web pages in google，but i can ’ t get the answer.So thank you very very much and it 's my first question in stackoverflow. — Jim Perfect, Oct 25 '17 at 13:33
*"and can we make `weekend` assigned `Saturday` and `Sunday`?"* -- only for the weeks when Saturday and Sunday are on the same day. — axiac, Oct 25 '17 at 16:59

Daniel Sęk · Answer 1 · 2017-10-25T18:33:25.987

It would be very messy to use same type for enumeration and collection of days. You should differentiate between WeekDay as symbols of days and collections of days as in Weekend. Look at int type. Variable int something could contain only one number. If you want more, you have to use collection: array, vector etc.

I assume that you want to create collections of week days where each day appears only once. For this we usually use sets.

This answer contains samples using std::set, then std::bitset, and custom class.

Sample for std::set.

#include <iostream>
#include <set>

enum WeekDay { Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday };

int main()
{
    std::set<WeekDay>   Weekend{ WeekDay::Saturday, WeekDay::Sunday };
    // For older compilers can be replaced with:
    // std::set<WeekDay>    Weekend;
    // Weekend.insert( WeekDay::Saturday );
    // Weekend.insert( WeekDay::Sunday );

    WeekDay today = WeekDay::Wednesday;

    // There is no Weekend.contains( today )
    // nor something likie Pascal
    // today in Weekend

    // Not so pretty
    if ( Weekend.find( today ) != Weekend.end() )
    //alternative:
    //if ( Weekend.count( today ) )
        std::cout << "Weekend :)\n";
    else
        std::cout << "Not weekend :(\n";
    return 0;
}

Unfortunately it isn't looking pretty or elegant. I'm open for improvement.

And std::bitset version:

#include <iostream>
#include <bitset>

enum WeekDay { Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday };

int main()
{
    // I don't like this. Number of elements = last element + 1.
    std::bitset<WeekDay::Friday+1>  Weekend;
    Weekend[ WeekDay::Saturday ] = true;
    Weekend[ WeekDay::Sunday ] = true;

    WeekDay today = WeekDay::Wednesday;

    if ( Weekend[ today ] )
        std::cout << "Weekend :)\n";
    else
        std::cout << "Not weekend :(\n";
    return 0;
}

And custom solution:

#include <iostream>
#include <assert.h>

enum WeekDay { Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday };

class WeekDays
{
public:
    WeekDays() : set( 0 ) {}

    // For older compilers just omit this constructor.    
    WeekDays( const std::initializer_list<WeekDay>& init )
        : set( 0 )
    {
        for ( auto it = init.begin() ; it != init.end() ; ++it )
            insert( *it );
    }

    void insert( WeekDay d )
    {
        assert( d >= WeekDay::Saturday && d < WeekDay::Friday && d >= 0 && d <= 31 );
        set |= 1 << d;
    }

    bool contains( WeekDay d )
    {
        assert( d >= WeekDay::Saturday && d < WeekDay::Friday && d >= 0 && d <= 31 );
        return ( set & ( 1 << d ) ) != 0;
    }

private:
    unsigned int    set;
};

int main()
{
    WeekDays    Weekend{ WeekDay::Saturday, WeekDay::Sunday };
    // For older compilers can be replaced with:
    // WeekDays Weekend;
    // Weekend.insert( WeekDay::Saturday );
    // Weekend.insert( WeekDay::Sunday );

    WeekDay     today = WeekDay::Wednesday;
    if ( Weekend.contains( today ) )
        std::cout << "Weekend :)\n";
    else
        std::cout << "Not weekend :(\n";
    return 0;
}

thank for your answer sincerely；And i will read it conscientiously. — Jim Perfect, Oct 25 '17 at 17:22

score -1 · Answer 2 · answered Oct 25 '17 at 13:41

-1

You can declare your enum as power of two. for E.g

enum weekdays {Saturday  =0 , Sunday = 1, Tuesday = 2,Wednesday = 4, Thursday = 8, Friday= 16} weekend;

And now you can assign more than one enum by using | operator between them.

To check if any enum is set use oprator &

answered Oct 25 '17 at 13:41

Geek

273
5
19

powers of 2 can get typos when they get large. I've always preferred `(1<<0)`, `(1<<1)`, `(1<<2)`, etc. Also, prefer that every name has at least one bit set (Your Saturday has no bits set). – Mooing Duck Oct 25 '17 at 18:16

How to assign multiple enum value to same enum variable in c++?

2 Answers2