Author: Tim Foden
Date: 06:14:00 07/21/04
Go up one level in this thread
On July 21, 2004 at 08:30:33, Daniel Shawul wrote:
>On July 21, 2004 at 06:42:23, Aivaras Juzvikas wrote:
>
>>On July 21, 2004 at 06:34:18, Daniel Shawul wrote:
>>
>>>On July 21, 2004 at 06:27:06, Paul Clarke wrote:
>>>
>>>>On July 21, 2004 at 06:16:10, Daniel Shawul wrote:
>>>>
>>>>>
>>>>>Isn't the size of a struct the sum of the sizes of its members.
>>>>>
>>>>>but for this struct sizeof(HASH_E) gives me 16 when i expect 14
>>>>>
>>>>>struct HASH_E
>>>>>{
>>>>> HASHKEY checksum;
>>>>> char from;
>>>>> char to;
>>>>> short eval;
>>>>> unsigned char depth;
>>>>> unsigned char entry_threat_promote_seq;
>>>>>};
>>>>
>>>>Structures are padded so that their size is a multiple of the largest alignment
>>>>size required by any of the members. In this case that would be the HASHKEY
>>>>which, depending on your architecture, the compiler will probably want to align
>>>>on a four- or eight-byte boundary, so the compiler adds a couple of extra bytes
>>>>to make the structure a multiple of four or eight bytes. The idea is that, if
>>>>you have an array of these structs, all the fields in all the elements of the
>>>>array will have the required alignment.
>>>
>>>Thanks very much.
>>>I changed the "struct member alignment" to 1 byte. Previously it was
>>>8 byte. And now it displays the correct size 14.
>>>Is there any efficiecy loss by changing the alignment?? If there is any
>>>i don't want to do that?
>>>
>>>daniel
>>
>>how did u change it?
>
>follow the link if you are using MSVC.
>
> project -> settings -> c/c++ -> catagory [code generation] -> struct member
>alignment.
>
>daniel
Rather than change the alignment for your whole project, perhaps it would be
better to just change it for the structures that you require to be packed.
In VC you can use this in your .h file (or wherever the struct is declared):
#pragma pack(push, 1)
struct
{
....
};
#pragma pack(pop)
Cheers, Tim.
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