On 25/07/14 03:01, darkjames-ws@xxxxxxxxxxxx wrote:
> Hi,
>
> On Thu, Jul 24, 2014 at 04:35:07PM -0400, Kevin Cox wrote:
>> 2: Change everything.
>> Pros:
>> - Full compiler error checking and type safety.
>> Cons:
>> - Hard
>> - May change dissector API.
>>
>> I was wondering what everyone else thought and what should be done to
>> improve the safety of this code.
>
> a/ For C90 (C99?) compilers (gcc/clang) use structure^W union initializer:
> instead of const void *strings;
>
> union {
> const void *data;
> const value_string *vs;
> value_string_ext *vse;
> const true_false_string *tfs;
> ...
> } u;
>
> add new macros to initialize this union correctly:
>
> #ifdef C_SUPPORTING_STRUCTURE_INITIALIZER
> #define VS_INIT(x) { .vs = x; }
> #define VSE_INIT(x) { .vse = x; }
> #else
> #define VS_INIT(x) { x }
> #define VSE_INIT(x) { x }
> #endif
>
> change VALS()/ TFS() macros to access union instead of cast.
This isn't bad but I don't think we want to require C99. Even msvcc
isn't too good at C99.
>
> b/ For any compiler:
> instead of const void *strings;
>
> do: const struct field_extension *field_ext;
>
> struct field_extension { int type; }
>
> #define FIELD_EXT(vs) &(vs).base
>
> struct field_extension_vs { struct field_extension base; const value_string *vs; }
> #define FIELD_INITIALIZE_VS(vs) { { FIELD_EXT_VS }, vs }
>
> struct field_extension_vse { struct field_extension base; value_string_ext *vse; }
> #define FIELD_INITIALIZE_VSE(vse) { { FIELD_EXT_VSE }, vse }
>
I like this quite a lot. Traditional C inheritance. It might be best
to do a true vtable though.
struct field_ext_type {
const char *(*to_str)(field_ext *self, int val);
...
};
struct field_ext {
struct_field_ext_type *type;
};
>
> Q: Can we do b/ easier if we go to C++?
Yes, because C++ does all of the type-tracking and virtual functions for us.
>
> Q: Is a/ union initializer supported by all new modern C++ compilers?
> For MSVC (AFAIR only when compiling C++ code) I see it was supported in MSVC2005: http://msdn.microsoft.com/en-us/library/81k8cwsz%28v=vs.80%29.aspx
>
No clue.
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