Operator++ with enum class

**mariostg** · 04-28-2013

I have this in my header file:

Code:

    public:
        enum class Azimuth {NORD = 0,
            NE = 45,
            EST = 90,
            SE = 135,
            SUD = 180,
            SO = 225,
            OUEST = 270,
            NO = 310,
            UNSET=-1};

        Azimuth& operator++();

And this in my implementation file:

Code:

Bousole::Azimuth& Bousole::Azimuth::operator++ ()
{
    //*this = (*this==Azimuth::NO) ? Azimuth::NORD : *this+NE;
    return *this;
}

Upon compiling, it complains that Bousole::Azimuth is not a class or namespace

g++ -Wall -g -std=c++0x -I/usr/includes/c++/4.7.1 -c main.cpp -o main.o
g++ -Wall -g -std=c++0x -I/usr/includes/c++/4.7.1 -c Bousole.cpp -o Bousole.o
Bousole.cpp:5:49: error: ‘enum class Bousole::Azimuth’ is not a class or a namespace
Bousole.cpp:5:49: error: ‘Bousole::Azimuth& operator++()’ must have an argument of class or enumerated type
make: *** [Bousole.o] Error 1

**grumpy** · 04-29-2013

enums cannot have members, member functions, nor a this pointer. enum class does not change that.

Overloaded forms of operator++() for an enum (whether a vanilla enum or a C++11 enum class) would be defined like this.

Code:

// prefix form
OurEnum& operator++ (OurEnum &x)
{
     //   increment value of x here
    return x;
}


// postfix form
OurEnum operator++ (OurEnum &x, int)
{
     Bousole::Azimuth temp(x);
     //   increment value of x here
    return temp;
}

I must admit, in your case, I consider incrementing an enum with values 45 apart is not sensible. Incrementing does not mean "add 45".

**Elkvis** · 04-29-2013

Originally Posted by grumpy

Incrementing does not mean "add 45".

in the context of cardinal compass directions, and especially in the context of an enum representing those directions, it could. incrementing a pointer points it to the next object, and not necessarily the next byte in memory, so increment doesn't always mean +1 in every context of an operation. +1 to a cardinal direction logically implies +22.5, +45, or +90 degrees, depending on how fine you want the directions to be.

**mariostg** · 04-29-2013

@Elkvis
Yes indeed, that is the idea. As the dial is rotated clockwise, degrees increase by 45 and at NW position, reset to North. But for some reason I cannot make this work.
I think I am going to revert to good old switch for now.

**phantomotap** · 04-29-2013

NO = 310

O_o

How would it work if your granularity is 45 degrees?

Soma

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