CODEWITHSUNDEEP
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giannis101
giannis101

Reputation: 3

Setting value to enum

I'm a beginner in C++ so I'm sorry if this is super obvious, but I have an issue with assigning values to an enum. I've declared the enum like so in a header file: 

 enum face
    {   paramControlHeight = 40,
        paramLabelWidth    = 80,
        paramSliderWidth   = 300
    };

And tried assigning an integer. Needless to say it doesn't work:

paramControlHeight = 40;//Not assignable

After googling about for a while, I tried:

using type_of_p=decltype(paramControlHeight);

Which as I understand, should yield the type of paramControlHeight, and enable me to use

paramControlHeight=static_cast<type_of_p> (40);

But I get the same "un-assignable" error

If anyone could point me in the right direction I'd be very grateful

Upvotes: 0

Views: 74

Answers (2)

463035818_is_not_an_ai
463035818_is_not_an_ai

Reputation: 122458

I want to assign "paramControlHeight" which is inside my enum a different value. So, for example, it starts out as 40, but I would like to change it to 80 later on

You seem to misunderstand what enums are. You seem to expect the enum to behave like this

struct face
{   int paramControlHeight = 40;
    int paramLabelWidth    = 80;
    int paramSliderWidth   = 300;
};

face f;                     // create instance
f.paramControlHeight = 40;  // modify member

However, an enum is rather like a 

struct face
{   
    static const int paramControlHeight = 40;
    static const int paramLabelWidth    = 80;
    static const int paramSliderWidth   = 300;
};

Now back to your actual enum:

enum face
{   paramControlHeight = 40,
    paramLabelWidth    = 80,
    paramSliderWidth   = 300
};

Here paramControlHeight is an enumerator with the value 40. You cannot modify it. It is not meant to be modified. It is meant to enumerate. What you can do is:

face f{ paramControlHeight };   // create instance of face
f = paramSliderWidth;           // assign a different value to it

A more typical enum would be

enum face_parts {
    nose = 1,
    eye = 2,
    mouth = 3
};

That you could use like this

void print_face_part( face_parts fp ){
    if (fp == nose) std::cout << "nose";
    if (fp == eye) std::cout << "eye";
    if (fp == mouth) std::cout << "mouth";
}

In simple terms an enum lets you name and group constants. Note that since C++11 there are scoped enums that are more flexible and dont introduce the name of the enumerators in the enclosing namespace.

Upvotes: 2

Aykhan Hagverdili
Aykhan Hagverdili

Reputation: 29975

paramControlHeight, paramLabelWidth, paramSliderWidth are the values. You can't assign anything to them more than you can assign a value to 42.

Upvotes: 1

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