标签 c structure bit-fields
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我正在对我的 C 项目运行代码质量检查，该项目涉及具有位域的结构。我遇到了一种情况，根据 MISRA C 2004 标准，规则 # 6.4 - 是一种违规行为，内容如下: “6.4 位字段只能定义为 unsigned int 或 signed int 类型。” Microsoft Developer Network 上可用的文献 here断言这一点。 谁能解释为什么位域成员的数据类型需要签名或无符号整数？为什么不允许我执行以下操作，即使以下代码编译时没有警告:
typedef struct
{
char a: 4;
char b: 4;
char flag: 1;
}MY_STRUCT
最佳答案
主要原因是，如果你不显式声明signed或unsigned，你不知道该类型是否会被视为signed 或 unsigned 除非阅读实现对它所做的定义。这意味着如果不使用带有显式符号关键字的类型，就无法编写可移植代码。 (还要注意，将 char 用于位域类型指示符是使用实现定义的类型。)
A bit-field shall have a type that is a qualified or unqualified version of
_Bool,signed int,unsigned int, or some other implementation-defined type.…
A bit-field is interpreted as having a signed or unsigned integer type consisting of the specified number of bits.125)
125)As specified in 6.7.2 above, if the actual type specifier used is
intor a typedef-name defined asint, then it is implementation-defined whether the bit-field is signed or unsigned.
指的是:
¶4 The expression that specifies the width of a bit-field shall be an integer constant expression with a non-negative value that does not exceed the width of an object of the type that would be specified were the colon and expression omitted.
¶5 … except that for bitfields, it is implementation-defined whether the specifier
intdesignates the same type assigned intor the same type asunsigned int.
关于c - 为什么 C 中的位域需要定义为 unsigned int 或 signed int 类型，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/23987376/