Re: data structure question

[gumbold <gumbold@bonbon.net>]

Glynn Clements wrote:

>gumbold wrote:
>
>  
>
>>>>why somebody wants to write such thing
>>>>struct abc {
>>>>    __u16 a;
>>>>    __u16 b;
>>>>    char abc[0];
>>>>} __attribute__((packed));
>>>>Specialy for zerod array of chars.
>>>>        
>>>>
>>>A structure which ends with a zero-length array is intended for use as
>>>the "header" for a variable-sized block of data, e.g.:
>>>
>>>	struct abc *new_abc(__u16 a, __u16 b, const char *string)
>>>	{
>>>		int len = strlen(string);
>>>		struct abc *p = malloc(sizeof(struct abc) + len + 1);
>>>	
>>>		p->a = a;
>>>		p->b = b;
>>>		memcpy(p->abc, string, len + 1);
>>>	
>>>		return p;
>>>	}
>>>
>>>  
>>>      
>>>
>>So if my compiler can't handle such code, can i change it to
>>struct abc {
>>    __u16 a;
>>    __u16 b;
>>    char abc[1];
>>} __attribute__((packed));
>>    
>>
>
>Yes, although you would need to adjust the size calculation if you
>need to calculate the exact size of the overall block.
>
>Zero-length arrays aren't valid in C89, but are in C99. Also, gcc has
>supported them as an extension since long before it started supporting
>C99.
>
>  
>
So char abc[0] actualy pointer to chat? It should be 4 byte long on x86.
I can't see it with sizeof.