On Jun 8, 2011, at 9:20 PM, Julian Leviston wrote: > Tanks everyone for answering on this so much... > > Comment/Question below, > > On 09/06/2011, at 4:56 AM, Kevin Jones wrote: > >> I really don't understand what this means: >> >> typedef struct object *(*method_t)(struct object *receiver, ...); >> >> method_t is a pointer to a function that returns an object pointer and takes >> receiver and additional argument > > Thanks for this. Okay, I understand that, but why is there a "struct" in > there twice? considering object is defined as a struct earlier in the > piece... is it because they're object pointers? when specifying a struct > pointer, do you need to write "struct" even though you've previously > specified a struct with that name?
The latter. In C++ you only need to use struct when declaring the type. However, in C you need to explicitly use struct every time you want to refer to the type. One common idiom is to use a typedef while defining the type. In this case, you might write: typedef struct object object_t; typedef object_t *(*method_t)(object_t *receiver, ...); > > ... > struct vtable; > struct object; > struct symbol; > > typedef struct object *(*method_t)(struct object *receiver, ...); > ... > > This is my reasoning... a function pointer "fp" to a function returning an > int and taking an int "h" as an argument is as follows: > > int (*fp)(int h); > > Now, a function pointer "fp2" to a function returning a pointer to an > integer, taking an integer pointer "x" as an argument would go like this in > my mind: > > int *(*fp2)(int *x); > > Does typedef require that "struct" is included as part of its syntax? Nope. In your two examples above, you're declaring variables "fp" and "fp2" that can hold function-pointers of the specified type. Say that you want to define a variable "fp3" that can point to a function of the same type as "fp2". You could write: int *(*fp3)(int *x); Or you use a typedef before declaring both of them: typedef int *(*fp_t)(int *x); fp_t fp2; fp_t fp3; As you can see, using typedef doesn't require you to use struct; the only reason struct was required is that in C you always need to use it as part of the type-name. > My god, C obfuscates meaning and intention so "well". <sigh> Yeah, the function-pointer syntax is gnarly. Hopefully I got it right above ;-) Cheers, Josh > It was one of my first programming languages, yet I still find it incredibly > difficult. I guess it's just me coming to the sad realisation that I need to > know C (and Math) much better. > > Julian. > > _______________________________________________ > fonc mailing list > fonc@vpri.org > http://vpri.org/mailman/listinfo/fonc
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