结构体位对齐的问题

childman 2010-07-15 11:40:06

GCC编译器中定义如下：
struct iec_i {
u_char ft :1;
u_short ns :15;
u_char res :1;
u_short nr :15;
}__attribute__((__packed__));

struct iec_s {
u_char ft :1;
u_short res1 :15;
u_char res2 :1;
u_short nr :15;
}__attribute__((__packed__));

struct iec_u {
u_char ft :2;
u_char start_act :1;
u_char start_con :1;
u_char stop_act :1;
u_char stop_con :1;
u_char test_act :1;
u_char test_con :1;
u_char res1;
u_short res2;
}__attribute__((__packed__));

struct iechdr {
u_char start;
u_char length;
u_char raw[0];
union {
struct iec_i ic;
struct iec_s sc;
struct iec_u uc;
}fc;
}__attribute__((__packed__));

得出:
sizeof(struct iec_i)=4
sizeof(struct iec_u)=4
sizeof(struct iec_s)=4
sizeof(struct iechdr)=6

移植到BCB

#pragma pack(1)

struct iec_i {
u_char ft :1;
u_short ns :15;
u_char res :1;
u_short nr :15;
};

struct iec_s {
u_char ft :1;
u_short res1 :15;
u_char res2 :1;
u_short nr :15;
};

struct iec_u {
u_char ft :2;
u_char start_act :1;
u_char start_con :1;
u_char stop_act :1;
u_char stop_con :1;
u_char test_act :1;
u_char test_con :1;
u_char res1;
u_short res2;
};

struct iechdr {
u_char start;
u_char length;
u_char raw[0];
union {
struct iec_i ic;
struct iec_s sc;
struct iec_u uc;
}fc;
};

得出:
sizeof(struct iec_i)=6
sizeof(struct iec_u)=4
sizeof(struct iec_s)=6
sizeof(struct iechdr)=8

怎样才能做到跟GCC里一样的效果？

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ccrun.com 2010-07-15

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毛毛正解. 楼主可以结帖了. 毛毛+100

Waiting4you 2010-07-15

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struct iec_i {

    u_short ft :1;

    u_short ns :15; //把类型改成一样

    u_short res :1;

    u_short nr :15;

};



struct iec_s {

    u_short ft :1;

    u_short res1 :15;

    u_short res2 :1;

    u_short nr :15;

};



struct iec_u {

    u_char ft :2;

    u_char start_act :1;

    u_char start_con :1;

    u_char stop_act :1;

    u_char stop_con :1;

    u_char test_act :1;

    u_char test_con :1;

    u_char res1;

    u_short res2;

};



struct iechdr {

    u_char start;

    u_char length;

    u_char raw[0];

    union {

        struct iec_i ic;

        struct iec_s sc;

        struct iec_u uc;

    }fc;

};