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structure interpret

Posted on 2013-06-28
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Last Modified: 2013-06-28
typedef struct {
	u_int len;
	uint32_t *val;
} bits;

bits b*_obj;
b_obj->val[0];
b_obj->val[1];

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Can someone please give me an example with some values. I am confused why it is using [] operator on pointer to uint32_t
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Question by:perlperl
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4 Comments
 
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Accepted Solution

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jkr earned 2000 total points
ID: 39285590
>> I am confused why it is using [] operator on pointer to uint32_t

That's because

b_obj->val[1];

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and

b_obj->val + 1;

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are exactly the same. However, the above expressions are meaningless because

a) 'b_obj' (a pointer to 'bits') is never assigned a value
b) 'b_obj->val[1];' is a NUP expression since neither a value is read nor set.

That would make more sense if that was like

typedef struct {
	u_int len;
	uint32_t *val;
} bits;

bits b*_obj = some_memory_area; // or '= &some_variable;'
b_obj->val[0] = 0xff;
b_obj->val[1] = 0xff;
b_obj->len = 2;                         

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or

typedef struct {
	u_int len;
	uint32_t *val;
} bits;

bits b*_obj = some_memory_area; // or '= &some_variable;'
unit32_t v1 = b_obj->val[0];
uint32_t v2 = b_obj->val[1];
                                  

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Author Comment

by:perlperl
ID: 39285619
hmmm. so if the len = 3, I can also access b_obj->val[2]  Correct?
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LVL 86

Expert Comment

by:jkr
ID: 39285630
Yes, absolutely.
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Author Closing Comment

by:perlperl
ID: 39285646
Thanks!
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