Re: Dynamic value string

[Guy Harris <guy () alum mit edu>]

On Sep 9, 2011, at 9:49 AM, Sylvain Munaut wrote:

> My idea was to extend the value_string to include a 'DYNAMIC' version
> where a call back of the dissector would be called with the value and
> should return a string to display.
>
> Obviously that string would have to be g_malloc'ed by the callback and
> then g_free'ed by the caller. (or give a buffer to write into to the
> call back, but then there is a size limit).
>
> Is there any solution I missed ?

Well, at least in 1.6.x and later (I don't know whether this was supported in 1.4.x), doc/README.developer says:

        display
        -------
        The display field has a couple of overloaded uses. This is unfortunate,
        but since we're using C as an application programming language, this sometimes
        makes for cleaner programs. Right now I still think that overloading
        this variable was okay.

        For integer fields (FT_UINT* and FT_INT*), this variable represents the
        base in which you would like the value displayed.  The acceptable bases
        are:
   
                BASE_DEC,
                BASE_HEX,
                BASE_OCT,
                BASE_DEC_HEX,
                BASE_HEX_DEC,
                BASE_CUSTOM
   
        BASE_DEC, BASE_HEX, and BASE_OCT are decimal, hexadecimal, and octal,
        respectively. BASE_DEC_HEX and BASE_HEX_DEC display value in two bases
        (the 1st representation followed by the 2nd in parenthesis).

        BASE_CUSTOM allows one to specify a callback function pointer that will
        format the value. The function pointer of the same type as defined by
        custom_fmt_func_t in epan/proto.h, specifically:

          void func(gchar *, guint32);
   
        The first argument is a pointer to a buffer of the ITEM_LABEL_LENGTH size
        and the second argument is the value to be formatted.
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