__attribute__((packed)) misuse?

vRltwE (86)
I'm trying to limit the size of struct/enum by means of the __attribute__((packed)):

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enum LogIdentifier
{
    LogIdentifierHouseKeeping = 0x01,
    LogIdentifierMagnetometer = 0x02,
    LogIdentifierDiffMIPS = 0x03,
    LogIdentifierMIPS = 0x04,
    LogIdentifierDiffSMDH = 0x05,
    LogIdentifierSMDH = 0x06
} __attribute__((packed));


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enum DataSegmentMIPS {
    Counters_00_20 = 0x01,
    Counters_21_50 = 0x02,
    Counters_51_80 = 0x04
} __attribute__((packed));


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struct DownloadLogFileNormalMIPS  {
    unsigned char command;
    unsigned char subCommand;
    LogIdentifier logId;
    unsigned short entries_ago;
    unsigned short entries_download;
    unsigned char entries_skip;
    DataSegmentMIPS flag;
} __attribute__((packed));


This way I get DownloadLogFileNormalMIPS as big as 10 bytes, where I was expecting 9. I'm doing something wrong? How to make DownloadLogFileNormalMIPS fit in 9 bytes?
Peter87 (11226)
So you say sizeof(DownloadLogFileNormalMIPS) returns 10? Strange, for me it returns 9.

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#include <iostream>

enum LogIdentifier
{
    LogIdentifierHouseKeeping = 0x01,
    LogIdentifierMagnetometer = 0x02,
    LogIdentifierDiffMIPS = 0x03,
    LogIdentifierMIPS = 0x04,
    LogIdentifierDiffSMDH = 0x05,
    LogIdentifierSMDH = 0x06
} __attribute__((packed));

enum DataSegmentMIPS {
    Counters_00_20 = 0x01,
    Counters_21_50 = 0x02,
    Counters_51_80 = 0x04
} __attribute__((packed));

struct DownloadLogFileNormalMIPS  {
    unsigned char command;
    unsigned char subCommand;
    LogIdentifier logId;
    unsigned short entries_ago;
    unsigned short entries_download;
    unsigned char entries_skip;
    DataSegmentMIPS flag;
} __attribute__((packed));

int main()
{
	std::cout << sizeof(LogIdentifier) << std::endl; // 1
	std::cout << sizeof(DataSegmentMIPS) << std::endl; // 1
	std::cout << sizeof(DownloadLogFileNormalMIPS) << std::endl; // 9
}
AbstractionAnon (6954)
Can you change the order of the fields? It looks like you're getting a pad byte to force word alignment of the shorts. Move logId after entries_download.
vRltwE (86)
Peter87, I'm in a x64 win. Might that be the reason?

AbstractionAnon, Not possible to change the order.
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