Assigning values to enumerated types

enum options {Yes,No};

class A{
    int i;
    string str;
    options opt;
};


int main{
    A obj;
    obj.i=5;
    obj.s开发者_JS百科tr="fine";
    obj.opt="Yes"; // compiler error
}

How can assign const char * to opt?

Just do

   obj.opt=Yes;

This code:

   obj.opt="Yes";

attempts to assign a string literal (a completely different type) to an enum type, which C++ doesn't automagically convert for you.

How can assign const char * to opt?

You'll have to do this manually, I like to keep a set of free functions around for doing conversions like this with my enums, ie I'll wrap my enums in a namespace and provide some functions for working with them:

namespace options
{
   enum Enum {Yes,No,Invalid};
   Enum FromString(const std::string& str);
   // might also add ToString, ToInt, FromInt to help with conversions
}

Enum  FromString(const std::string& str)
{
    if (str == "Yes")
    { 
        return Yes        
    }
    else if (str == "No")
    {
        return No;
    }
    return Invalid; //optionally throw exception
}

Now you can do:

 class A{
   int i;
   string str;
   options::Enum opt; // notice change here
 };

 ...


obj.opt=options::FromString("Yes");

So you can see, enums in C++ probably don't give you all the bells and whistles of enums in other languages. You'll have to manually convert things yourself.

Enums are not strings, but just values

obj.opt = Yes;

Because an enum value is not a string. This is correct :

int main{
    A obj;

    obj.opt=Yes;
}

You can't do this. You will have to use some string comparisons and set it.

In your case you can "convert" enum to const char*. All what you need is to create macro. For example: #define ENUM_TO_CSTR(x) #x and then: obj.opt=ENUM_TO_CSTR(Yes).

This macro will convert everything you pass to it into C-like string. It won't convert variable value, but only its name!

int x = 10; cout << ENUM_TO_CSTR(x) << endl;

Will print x (not 10) on screen, so be careful using it!

When you try to assign "Yes" it means that you are trying to assign a string value and not the enum constant from the enum options. Instead use the syntax:

    obj.opt = Yes;

Try printing the value of opt from obj:

    cout << obj.opt;

You will get the output as 0, since enum indices start from 0. Yes is 0 and No is 1.