Hi Dustin,
Thanks for the answer.
Very useful. I think I understand the offsetof macro... tricky,
smart ;-)
offset = (size_t) &((struct mystruct *)0)->B
I will use it to continue understanding how structures are stored in
memory.
Miguel Angel
Tuesday, April 6, 2004, 5:41:20 PM, you wrote:
DL> hi,
DL> maybe the "offsetof" macro will help you.
DL> it's sort of like "sizeof", except it tells you the offset of a variable
DL> within a structure.
DL> for example,
DL> struct mystruct {
DL> unsigned int A;
DL> char* B;
DL> };
DL> mystruct st;
DL> char* pB = (char*)&st + offsetof(struct mystruct, B);
DL> should set "pB" to be a pointer to member "B" within structure "st".
DL> you can find the definition of "offsetof" in "stddef.h" - you should be
DL> able to understand how it works.
DL> cheers,
DL> dstn.
>> Hello experts,
>>
>> I have a problem ;-) I have a structure, its first field being a 8 bits
>> type.
>>
>> struct {
>> U8 firstfield;
>> .
>> .
>> .
>> } st;
>>
>> char* p = &st;
>>
>> If I access the structure through a char pointer, am I accesing the
>> first 8 bits field?? The first field will always be stored at the
>> first byte (the one pointed by p)? This depends on the compiler?
>>
>> The origin of the problem: I have a function with an only one
>> argument, but I have to pass several kind of types through that
>> argument. I first thougth the argument to be a union containing all
>> the possible types. But it is really a lot of types.
>>
>> I try the argument to be a char array. I will pass a first byte
>> being a kind of index to identify the type. Following the first byte
>> it is the type byte per byte. Inside the function I can examine the
>> first byte and decide to do a cast, according to the correct type,
>> to format the rest of bytes.
>>
>> Thanks a lot,
>> Miguel Angel
>>
