structure compare

what different between :
====

struct *structptr;

-vs-

struct structptr;

??

and then how about the used for the typedef int <variable>, and int <variable> ??

Could you describe your question in a different manner? I find it difficult to understand.

p.s. I love your avatar, it's adorable. :D

-Prelude

One is a pointer to an object. One isn't.
[edit] Or they would be, if that was valid code... [/edit]

Quzah.

[prelude] p.s. I love your avatar, it's adorable
reply : oh heee, my friends copy it to me. LOL thx

--

[quzah]
reply :
meaning ? actually the code will found mostly on the stucture.

name *structptr;

>> is it used for pointer? pointer to pointer ? and how're they work ?

name structptr;

>> is it also pointer too? or just a reference? ermm... so isn't the upper code 's function still the same, but the usage is different? could you describe more detail with the source code? pls...

here's the eg. u wanted

Code:

---

#include<stdio.h>
 #include<alloc.h>
typedef struct data
 {
 int  num;
 }object;

void main()
  {
        object *first;
        object second;
        puts("Enter two numbers :");
                first= (object *)malloc(4);
        scanf("%d %d",&first->num,&second.num);
        puts("Entered data :");
        printf("%d %d",first->num,second.num);
 }

---

" object " is the typedefinition.
Hadn't it been used u would always have to go for long stmts like

struct data *first,second ;
It's also useful when u go for type qualifiers like unsigned long int...

Code:

---

object *first;
object second;

---

the first stmt is a pointer to the structure(in this case ,object)
i.e first will contain the address of a structure.u need to use the arrow operator to access the members in this case.

the second one is an ordinary structure variable.

>>here's the eg. u wanted
No it's not.

>>void main
void main is wrong, please don't promote it's use.

>>#include<alloc.h>
What are you using it for? why not stdlib.h?

>>first= (object *)malloc(4);
You malloc'd 4 bytes. How do you know that sizeof(object) is only 4 bytes? Your use of malloc is wrong here, it should be
>>first=malloc(sizeof(*first));

>>scanf("%d %d",&first->num,&second.num);
Don't forget to check the return from scanf() to ensure it did what you asked it to.

Quote:

---

Originally posted by Hammer
>>first= (object *)malloc(4);
You malloc'd 4 bytes. How do you know that sizeof(object) is only 4 bytes? Your use of malloc is wrong here, it should be
>>first=malloc(sizeof(*first));

---

I'd say it's better to use sizeof(object). To use the actual structure, not the instance of it.
But it's basically the same thing...

Quote:

---

Originally posted by Magos
I'd say it's better to use sizeof(object). To use the actual structure, not the instance of it.
But it's basically the same thing...

---

Fair enough.... there's another thread on that particular matter somewhere... either way is fine by me. I was just highlighting the fact that hard coding a numeric as the size of the structure is wrong.

>I'd say it's better to use sizeof(object).
This is not just a style issue, many people prefer

T *mem = malloc ( sizeof *mem );

because it minimizes the number of items you need to change with an update. This is not as much an issue with a text editor that can find and replace text, but it is still considered good style. Now, it still is a pretty big style issue even though there are distinct maintanability reasons for not using sizeof ( structure ), so use what you feel comfortable with. Though I can pretty much guarantee that I or someone else on comp.lang.c will suggest you use sizeof ( *instance ) for this and other reasons. ;)

I now return you to your regularly scheduled thread.

-Prelude

Quote:

---

" object " is the typedefinition.

---

object is a type alias to the type struct data.
A type is a set of values and a set of operations. So like for a type int, the set of values is
[INT_MIN, INT_MAX] and the set of operations is
{+, -, +=, -=, ++, --, *, /, %}

this statement is wrong ..
>> scanf ("%d",&board->value); //something like that!

correction is ...

>> scanf ("%d",&(board->value));

Quote:

---

Originally posted by beely
this statement is wrong ..
>> scanf ("%d",&board->value); //something like that!

correction is ...

>> scanf ("%d",&(board->value));

---

No it isn't. The first is not incorrect. It's perfectly valid.

Quzah.

Quote:

---

this statement is wrong ..
>> scanf ("%d",&board->value); //something like that!

correction is ...

>> scanf ("%d",&(board->value));

---

Both calls to scanf are equivalent. The -> operator has higher precedence than the address-of operator, so the indirection is always performed first unless you use parens to force taking the address first:

(&board)->value

Which in this case would be an error, but you could be creative and do something like this to make it work:

scanf ( "%d", &(*&t)->value );

Though I don't recommend it.

-Prelude