Re: C question

al davis wrote:
> I ran into this in ngspice code ...
> 
> A structure ....
> 
> typedef struct SPICEdev {
>     int (*DEVparam)(int,IFvalue*,GENinstance*,IFvalue *);  
>     int (*DEVmodParam)(int,IFvalue*,GENmodel*);   
>     int (*DEVload)(GENmodel*,CKTcircuit*);   
>     int (*DEVsetup)(SMPmatrix*,GENmodel*,CKTcircuit*,int*);   
> } SPICEdev; 
> 
> is initialized like this ....
> 
> SPICEdev CCCSinfo = {
>     DEVparam      : CCCSparam,
>     DEVmodParam   : NULL,
>     DEVload       : CCCSload,
>     DEVsetup      : CCCSsetup
> };
> 
> I would expect this (as it is in Spice 3f5) ....
> 
> SPICEdev CCCSinfo = {
>     CCCSparam,
>     NULL,
>     CCCSload,
>     CCCSsetup
> };
> 
> 
> The way it is done in ngspice is certainly an improvement, but I 
> could not find any documentation for that syntax.  It obviously 
> works, at least with gcc.  Is this a gcc extension?  Can 
> someone point me to some official documentation?
> 
> I am not looking for an explanation of how this feature works 
> and why to use it.  It is obvious to me.  I am looking for a 
> reference to official documentation. It is a good feature, that 
> I would like to use, but I will only use it if it is part of 
> the official language.

Using a colon in an initializer is an obsolete GCC syntax.  C99
now allows for designated initializers.  See
http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html


In a structure initializer, specify the name of a field to initialize with `.fieldname =' before the element value. For example, given the following structure,

     struct point { int x, y; };

the following initialization

     struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

     struct point p = { xvalue, yvalue };

Another syntax which has the same meaning, obsolete since GCC 2.5, is `fieldname:', as shown here:

     struct point p = { y: yvalue, x: xvalue };


galen