CODEWITHSUNDEEP
c++
ffenix
ffenix

Reputation: 553

Type int on struct error

I got the following struct:

struct Packet
{
    short PacketSize;
    short Type;
};

struct SizeValidity
{
    short SizeEnc;
};

struct SendEncSecureCode
{
    Packet header;
    short EncSecurityToken;
    int lTime;
    SizeValidity ending;
};

And on my code i want to get the size of the struct with the sizeof operator like this:

SendEncSecureCode sendpacket;
sendpacket.header.PacketSize = sizeof SendEncSecureCode;

Problem is i always get size 0x10 instead of 0x0C i am specting, so i change the INT type to DWORD and still the same problem, later i try with DWORD32 and still the same, the compiler is setting it as 8 bytes. I am working on VC11 Beta and the soft is aim to x86 not x64. Thanks

Upvotes: 1

Views: 124

Answers (2)

Mahmoud Al-Qudsi
Mahmoud Al-Qudsi

Reputation: 29529

This is called padding. The compiler pads the space between the different members of the structure with zero bytes to better-align the members to addresses that can be read quicker by the CPU. You can (but should not unless you have a very good reason) override this behavior with the pack pragma:

#pragma pack(push, 0)
struct {...};
#pragma pack(pop)

This forces the padding for this struct to be zero bytes. You can change the zero around.

Upvotes: 3

craig65535
craig65535

Reputation: 3582

To get the size you're expecting, you can tell the compiler to use 1-byte packing:

#pragma pack(push, 1)
struct Packet
{
    short PacketSize;
    short Type;
};

struct SizeValidity
{
    short SizeEnc;
};

struct SendEncSecureCode
{
    Packet header;
    short EncSecurityToken;
    int lTime;
    SizeValidity ending;
};
#pragma pack(pop)

Please see http://vcfaq.mvps.org/lang/11.htm

Upvotes: 0

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