double a;
    int    b;
    char   c;
};
#pragma pack()

void main()
{
    printf( "sizeof( struct abc ) = %d\n", sizeof( struct abc ) );
}

以上代碼
gcc tBytePadding.c -o tBytePadding
Ubuntu執(zhí)行結(jié)果：sizeof( struct abc ) = 13

/usr/local/arm/2.95.3/bin/arm-linux-gcc -I /usr/local/arm/2.95.3/arm-linux/include tBytePadding.c -o tBytePadding
執(zhí)行結(jié)果：sizeof( struct abc ) = 16 <-- 依然四字對(duì)齊了,，沒有一字節(jié)對(duì)齊

方法二：

#include <stdio.h>

typedef struct tagabc
{
    double a;
    int    b;
    char   c;
}__attribute__( ( packed, aligned( 1 ) ) ) abc;

void main()
{
    printf( "sizeof( abc ) = %d\n", sizeof( abc ) );
}

或

#include <stdio.h>

struct abc
{
    double a;
    int    b;
    char   c;
}__attribute__( ( packed, aligned(1) ) );

void main()
{
    printf( "sizeof( struct abc ) = %d\n", sizeof( struct abc ) );
}

以上代碼
gcc tBytePadding.c -o tBytePadding
Ubuntu執(zhí)行結(jié)果：sizeof( struct abc ) = 13

/usr/local/arm/2.95.3/bin/arm-linux-gcc -I /usr/local/arm/2.95.3/arm-linux/include tBytePadding.c -o tBytePadding
執(zhí)行結(jié)果：sizeof( struct abc ) = 13

推薦使用方法二的第一種,！

注意：
typedef struct tagabc
{
    double a;
    int    b;
    char   c;
}__attribute__( ( packed, aligned( 1 ) ) );

tagabc abc;

以上寫法會(huì)報(bào)此錯(cuò)誤：warning: ‘packed’ attribute ignored

typedef struct tagabc
{
    double a;
    int    b;
    char   c;
} abc __attribute__( ( packed, aligned( 1 ) ) );