Question

我正在使用具有此结构的多个程序员之间共享的文件：

typedef struct _APPLE{
   ULONG appleID;
   struct{
       ULONG isBig: 1;
       ULONG isRed: 1;
       ULONG isFresh: 1;
       ULONG isGood: 1;
       ULONG bReserved: 28;
   };
}APPLE;

由于文件是共享的，我无法编辑它。我想在我的代码中使用这个APPLE结构，并希望为每个成员提供值。我怎么能这样做？

Answer 1

首先，你不能在标准C中使用匿名嵌套结构，它是某些编译器使用的扩展。

所以你必须命名你的位字段结构：

typedef struct _APPLE{
   ULONG appleID;
   struct{
       ULONG isBig: 1;
       ULONG isRed: 1;
       ULONG isFresh: 1;
       ULONG isGood: 1;
       ULONG bReserved: 28;
   } flags;
}APPLE;

然后只需使用普通的点符号来访问字段：

APPLE apple;
apple.appleID = 5;
apple.flags.isBig = 1;
apple.flags.isRed = 0;

虽然位字段的多个成员可能共享相同的int，但它们仍然彼此分离。因此，更改位域的一个成员不会改变任何其他成员。

Answer 2

根据 ISO / IEC 9899：2011 ，§6.7.2.1结构和联合说明符

An implementation may allocate any addressable storage unit large enough to hold a bitfield. If enough space remains, a bit-field that immediately follows another bit-field in a structure shall be packed into adjacent bits of the same unit. If insufficient space remains, whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is implementation-defined. The order of allocation of bit-fields within a unit (high-order to low-order or low-order to high-order) is implementation-defined. The alignment of the addressable storage unit is unspecified.

如何使用带位字段的结构

2 个答案: