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]

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 ??

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]

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.

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]

How does this establish defaults?

Consider:

#include <iostream>

enum Color {red, white, blue};

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

Took the question wrong..my bad.

 

[Sharad Kala]

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 ??

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]

hi there,
[...]

actually i m having an Array of enums...

 

[Max M.]

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 ??

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,Mary> ev;
ev = v;
v = ev;
if( ev == v ) { }
if( ev == John ) { }
switch( ev )
{
case Mary:
case John: ;
}
}

Max

 

[Sharad Kala]

hi there,
[...]

actually i m having an Array of enums...

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 << "\n";
}

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

Best wishes,
Sharad

 

[torhu]

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

 

[Sharad Kala]

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

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