default values to enum ?

[dumboo]

hi there,

i was looking for some way to give default values to enum, when ever i m
creating an enum variable it shuld be INITIALIZED to certain default values
is it possible ? or do i have to write some function for assigning values to
them and call them myself ??

[Sharad Kala]

Re: default values to enum ?


"dumboo" <vthe2@yahoo.co m> wrote in message
news:c19ges$1fi eab$1@ID-211285.news.uni-berlin.de...[color=blue]
> hi there,
>
> i was looking for some way to give default values to enum, when ever i m
> creating an enum variable it shuld be INITIALIZED to certain default values
> is it possible ? or do i have to write some function for assigning values to
> them and call them myself ??[/color]

Enum values do have defaults.
Consider enum Color {red, white, blue};
In this case red will be 0, white will be 1 and blue will be 2.

For more -

http://www.parashift.com/c++-faq-lite/newbie.html#faq-29.18

Best wishes,
Sharad

[Jonathan Turkanis]

Re: default values to enum ?


"Sharad Kala" <no.spam_sharad k_ind@yahoo.com > wrote in message
news:c19hfo$1fi ru0$1@ID-221354.news.uni-berlin.de...[color=blue]
>
> "dumboo" <vthe2@yahoo.co m> wrote in message
> news:c19ges$1fi eab$1@ID-211285.news.uni-berlin.de...[color=green]
> > hi there,
> >
> > i was looking for some way to give default values to enum, when[/color][/color]
ever i m[color=blue][color=green]
> > creating an enum variable it shuld be INITIALIZED to certain[/color][/color]
default values[color=blue][color=green]
> > is it possible ? or do i have to write some function for assigning[/color][/color]
values to[color=blue][color=green]
> > them and call them myself ??[/color]
>
> Enum values do have defaults.
> Consider enum Color {red, white, blue};
> In this case red will be 0, white will be 1 and blue will be 2.[/color]

How does this establish defaults?

Consider:

#include <iostream>

enum Color {red, white, blue};

int main()
{
Color c;
std::cout << "default Color = " << c <<" \n";
}

Try this on a couple of compilers.

Jonathan

[Sharad Kala]

Re: default values to enum ?


"Jonathan Turkanis" <technews@kanga roologic.com> wrote in message
news:c19ic8$1fl 5b8$1@ID-216073.news.uni-berlin.de...[color=blue]
>
> "Sharad Kala" <no.spam_sharad k_ind@yahoo.com > wrote in message
> news:c19hfo$1fi ru0$1@ID-221354.news.uni-berlin.de...[color=green]
> >
> > "dumboo" <vthe2@yahoo.co m> wrote in message
> > news:c19ges$1fi eab$1@ID-211285.news.uni-berlin.de...[color=darkred]
> > > hi there,
> > >
> > > i was looking for some way to give default values to enum, when[/color][/color]
> ever i m[color=green][color=darkred]
> > > creating an enum variable it shuld be INITIALIZED to certain[/color][/color]
> default values[color=green][color=darkred]
> > > is it possible ? or do i have to write some function for assigning[/color][/color]
> values to[color=green][color=darkred]
> > > them and call them myself ??[/color]
> >
> > Enum values do have defaults.
> > Consider enum Color {red, white, blue};
> > In this case red will be 0, white will be 1 and blue will be 2.[/color]
>
> How does this establish defaults?
>
> Consider:
>
> #include <iostream>
>
> enum Color {red, white, blue};
>
> int main()
> {
> Color c;
> std::cout << "default Color = " << c <<" \n";
> }
>[/color]
Took the question wrong..my bad.

[Sharad Kala]

Re: default values to enum ?


"dumboo" <vthe2@yahoo.co m> wrote in message
news:c19ges$1fi eab$1@ID-211285.news.uni-berlin.de...[color=blue]
> hi there,
>
> i was looking for some way to give default values to enum, when ever i m
> creating an enum variable it shuld be INITIALIZED to certain default values
> is it possible ? or do i have to write some function for assigning values to
> them and call them myself ??[/color]

I don't know of a way to default initialize an enum variable.
Probably someone could tell how to achieve what he has asked for.

If the enum is part of a class then probably this could be a solution -

#include <iostream>
enum Color {red = 34, white = 42, blue = 55 };

struct A{
Color c;
A():c(white){
}
A(Color C):c(C){}
};

int main()
{
A a;
std::cout << "default Color = " << a.c <<" \n";
A b(blue);
std::cout << "Color = " << b.c <<" \n";
}

[dumboo]

Re: default values to enum ?

hi there,
"Sharad Kala" <no.spam_sharad k_ind@yahoo.com > wrote in message
news:c19nfn$1el udo$1@ID-221354.news.uni-berlin.de...
[...]

actually i m having an Array of enums...

[Max M.]

Re: default values to enum ?

dumboo wrote:
[color=blue]
> hi there,
>
> i was looking for some way to give default values to enum, when ever i m
> creating an enum variable it shuld be INITIALIZED to certain default
> values is it possible ? or do i have to write some function for assigning
> values to them and call them myself ??[/color]


enum Foobars
{
John, Mary
};


template< typename EnumT, EnumT DefaultV >
class Enum
{
EnumT value;
public:
Enum( EnumT v = DefaultV ) : value(v) { }
operator EnumT() const { return value; }
};

int main()
{
Foobars v = John;
Enum<Foobars,Ma ry> ev;
ev = v;
v = ev;
if( ev == v ) { }
if( ev == John ) { }
switch( ev )
{
case Mary:
case John: ;
}
}

Max

[Sharad Kala]

Re: default values to enum ?


"dumboo" <vthe2@yahoo.co m> wrote in message
news:c19nnm$1g0 6e8$1@ID-211285.news.uni-berlin.de...[color=blue]
> hi there,
> "Sharad Kala" <no.spam_sharad k_ind@yahoo.com > wrote in message
> news:c19nfn$1el udo$1@ID-221354.news.uni-berlin.de...
> [...]
>
> actually i m having an Array of enums...[/color]

Does this help?

#include <iostream>
enum Color {red = 34, white = 42, blue = 55 };
struct Enum{
Color c;
Enum(Color c):c(c){}
Enum():c(white) {}
Enum& operator=(Color col)
{
this->c = col;
return *this;
}
operator Color(){
return c;
}
};

int main(){
Enum c[10];
c[7] = blue;
c[5] = red;
for (int i=0; i<10; i++)
std::cout << c[i] << "\n";
}

Output -
42
42
42
42
42
34
42
55
42
42

Best wishes,
Sharad

[torhu]

Re: default values to enum ?

Since you have the conversion constructor Enum(Color c), you don't really need the
operator=() either. :)

[Sharad Kala]

Re: default values to enum ?


"torhu" <thusaboe@hotma il.com> wrote in message
news:25b320.040 2221313.56b27a2 c@posting.googl e.com...[color=blue]
> Since you have the conversion constructor Enum(Color c), you don't really need[/color]
the[color=blue]
> operator=() either. :)[/color]

True, I would expect ideally two invocations, namely constructor and
copy-constructor in this case.
With assignment operator I would expect just one call.
I know most compilers do elide the copy-constructor part.
If I make the copy constructor private I should expect the program to break,
provided no assignment operator is defined.

Section 12.8/14
"A program is ill-formed if the copy constructor or the copy assignment operator
for an object is implicitly used and the
special member function is not accessible"

To my surprise Comeau online and g++ 3.3.1 don't think alike.
Thankfully VC 7 agrees with me :-)
Am I missing on something?

Best wishes,
Sharad