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Struct Declaration

Posted on 2004-03-24
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Last Modified: 2010-04-15
Let say we have this struct:
struct foo {
   int x;
   int y;
   int z;
};

In Linux, we can do

Case 1:
struct foo f = {
   x : 1,
   y : 2,
   z : 3,
};

Case 2:
struct foo f = {
   x : 1,
   z : 2,
   y : 3,
};  /* Note y and z are switched */

In Windows, with Case 1, I can initialize that have the same result. However, with Case 2, how can I do it when z and y are switched since Windows doesn't like
struct foo f = {
  parameter : value,
  ...........
};

Thanks!
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Question by:beneflex
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8 Comments
 
LVL 1

Expert Comment

by:beavis_shenzhen
ID: 10673577
the constructor of struct foo is nothing to do with the OS, Win or Linux.

consider:
switch(No)
{
    case 1:
    {
        struct foo f;
        f.x = 1;
        f.y = 2;
        f.z = 3;
        ...........
        break;
    }
    case 2:
    {
        struct foo f;
        f.x = 1;
        f.y = 3;
        f.z = 2;
        ...........
        break;
    }
}
0
 
LVL 8

Expert Comment

by:ssnkumar
ID: 10674269
"Case 2" (switching of y and z) is not implemented in C++ (it is not the problem with windows)!
The struct under C and struct in C++ are implemented differently!
In C++, when you initialize a structure it calls a constructor (which is not the case in C) and the values of initialization are passed as parameters to this constructor and these have to be in the same order as in the constructor!

You can try something like this:
struct foo
{
   int x;
   int y;
   double z;
   foo(int a, int b, double c) { x = a; y = b; z = c;}
   foo(int a, double b, int c) { x = a; y = c; z = b;}
};

main()
{
        foo f(1, 2, 3.0), f1(1, 2.0, 3);
}


-ssnkumar
0
 
LVL 8

Expert Comment

by:akshayxx
ID: 10674498
seems you got the answer from ssnkumar,
still just out of curiosity, why would you do that ( switching the inializer variables)..
why do you want to twist the things around? When they work absolutely fine done straight away.
that will make the code less readable for reviewers.
(may be you find it more pleasurable to hold the ear around the head ;-P)..


akshay
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LVL 5

Expert Comment

by:dennis_george
ID: 10674645
Hi,

what you have given

struct foo f = {
   x : 1,
   y : 2,
   z : 3,
};

is memberwise assignment which is only present in linux and is not a ANSII standard (I think it might be the C99 standard).

In Windows environment or the compiler which only support ANSII you have to assign the structure value individually as shown by  beavis_shenzhen...

If you want to initialize all the variables then you can use the asignment operator

struct foo f = {1, 2, 3} ;
or
struct foo f = {1, 3, 2} ;

Hope you got it
Dennis
0
 
LVL 5

Expert Comment

by:dennis_george
ID: 10674646
Hi,

what you have given

struct foo f = {
   x : 1,
   y : 2,
   z : 3,
};

is memberwise assignment which is only present in linux and is not a ANSII standard (I think it might be the C99 standard).

In Windows environment or the compiler which only support ANSII you have to assign the structure value individually as shown by  beavis_shenzhen...

If you want to initialize all the variables then you can use the asignment operator

struct foo f = {1, 2, 3} ;
or
struct foo f = {1, 3, 2} ;

Hope you got it
Dennis
0
 
LVL 5

Expert Comment

by:dennis_george
ID: 10674655
Oops I entered it twice.... may be I refereshed it after i submitted ....
Sorry for that

Dennis
0
 
LVL 12

Accepted Solution

by:
stefan73 earned 2000 total points
ID: 10676294
Hi beneflex,
> struct foo f = {
>    x : 1,
>    y : 2,
>    z : 3,
> };

That's not a question of Windows or Linux, but a question of the used compiler. GCC in Linux has tons of extension, so sometimes it's not transparent why GCC jumps through the hoop and VC++ doesn't.

Try the GCC manual:
http://gcc.gnu.org/onlinedocs/gcc-3.3.3/gcc/

Cheers,

Stefan
0
 
LVL 12

Expert Comment

by:stefan73
ID: 10676305
BTW: If you want all those fancy GCC extensions in Windows, try the cygwin environment:

http://www.cygwin.com

It comes with GCC and compiles a lot of Linux sources out-of-the-box.
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