Em 16/4/2010 11:22, Byron Jeff escreveu:
> On Thu, Apr 15, 2010 at 11:23:21PM -0400, Justin Richards wrote:
>   =

>>> it. For example I would have declared the stuct above as:
>>>
>>> typedef struct Temp
>>> {
>>>    unsigned char  Var00;
>>>    unsigned char  Var01;
>>>    unsigned char  Var02;
>>>    unsigned char *Var03;
>>> } Temp_t, *Temp_p;
>>>
>>> This creates two new types named Temp_t, which is the structure, and
>>> Temp_p, which is a pointer to that type of structure. From then on you =
can
>>> use those names getting rid of that horrid struct keyword. For example
>>> instead of:
>>>
>>> Temp_t new1, new2; // Much cleaner.
>>>
>>> Seeking more clarification here.
>>>       =

>> I get the pointer thing to some degree.  Passing address to variables ra=
ther
>> than passing the values of the variables.  And a pointer contains the
>> address of a variable and I can see that Temp_t is of type struct as def=
ined
>> above but what is *Temp_p.
>>     =

> Defined as a pointer to the struct. Useful when you want to pass the stru=
ct
> around in a function and change its contents. For example.
>
> void new_var00(Temp_p target,unsigned char testval)
> {
>    target->Var00 =3D testval;
> }
>
>   =

>> I assume *Temp_p does not set aside or allocate memory to which it point=
s to
>> or does it.
>>     =

> It does not. There's another trick I use for that. Arrays in C allocate
> space and the name represents a pointer to that space. So while lost folks
> who wanted to use the new_var00 function above would do something like:
>
> void main()
> {
>    Temp_t mine;
>
>    new_var00(&mine,14);
> }
>
> Having to do the address of operator always drove me nuts. So instead I
> would do the following:
>
> void main()
> {
>    Temp_t fixed[1];
>
>    new_var00(fixed,18);
> }
>
> Allocating an array with one element gives the space for a single structu=
re
> but the much more convenient handle of a pointer to the structure for the
> name.
>
>   =

>> If it is a pointer to that type of structure when do you use it, inside
>> another structure perhaps?.
>>     =

> See above. All of it is just simplifying the syntax around the restrictio=
ns
> that C puts upon you. =

>
>   =

>> To delare a pointer to the start of a memory
>> location with that type of structure.
>>     =

> You can do that too of course if you want to dynamically allocate
> structures. But as you can see, even if you are only using it for paramet=
er
> management, declaring a pointer to the struct is still a good thing to do=
. =

>
> My real objective is to never have to use the struct keyword anywhere els=
e in
> the program other than in the typedef delcaration. To accomplish that, a
> name has to be attached to the struct pointer type in addition to the
> struct type even if the context is only for parameter passing in function=
s.
>
> The vast majority of my programs never use the dot operator for structs.
> Virtually every structs name is attached to a pointer and the arrow
> operator (->) is my best friend.
>
>   =

>> Like
>>
>> Temp_p a_new_pointer;
>>
>> a_new_pointer =3D &new1;
>>     =

> Presuming that new1 is a struct. But to reiterate you can get both space
> and a pointer to that space simply be declaring a single element array.
> i.e.
>
> Temp_t new1[1];
>
> Now new1 is a pointer to the allocated first element. No need to track two
> different names.
>   =


You just replaced one annoyance by another, now you need to use
"new1[0].Var00" and so on.

Isaac
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