结构和联合名称冲突

Question

我写了一个简单的测试程序并尝试使用这个：

union FLT { ... };
struct FLT { ... };

但是编译器抱怨命名冲突。

因为在 C 中你需要使用 struct 和 union 作为你的标签名称，为什么它们会冲突？

我的意思是当我们想要声明一个名为 num 的 stuct FLT 类型的变量时，我们会使用

struct FLT num;

并且当我们想要使用类型为 union FLT 的名为 diffnum 的变量时，我们将使用

union FLT diffnum;

那么为什么编译器不能区分它们呢？

顺便说一句，我测试了 MinGW 和 VC，如果你需要知道的话。

更新

union FLOAT {
        float value;
        unsigned int bits;
        unsigned char bytes[4];
};
struct FLOAT {
        unsigned int sign;
        unsigned int exponent;
        unsigned int significand;
};
union FLOAT num;
struct FLOAT num_parts;

我正在使用这段代码做一些浮点运算测试。

Answer 1

它们会发生冲突，因为所有 "tagged types" 标签共享同一个命名空间。

C11 6.2.3 Name spaces of identifiers (N1570 Draft)

If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate name spaces for various categories of identifiers, as follows:

label names (disambiguated by the syntax of the label declaration and use);

the tags of structures, unions, and enumerations (disambiguated by following any of the keywords struct, union, or enum);

the members of structures or unions; each structure or union has a separate name space for its members (disambiguated by the type of the expression used to access the member via the . or -> operator);

all other identifiers, called ordinary identifiers (declared in ordinary declarators or as enumeration constants).

结构和联合名称冲突

struct and union name collision

c

struct

unions