了解同一范围内的声明
Understanding declarations in the same scope
这是一个关于 ISO C 的语言律师问题。
我想了解标准中是如何定义声明的。我使用 N1570。考虑以下情况：
案例一.
int a;
extern int a; //compatible types, external linkage, well-defined behavior
案例二.
extern int a;
int a; //well-defined behavior, external linkage, well-defined behavior
案例三.
int a;
static int a; //6.2.2/6.9.2UB, linkage-disagreement
案例4.
static int a;
extern int a; //6̶.̶2̶.̶2̶/̶6̶.̶9̶.̶2̶ ̶U̶B̶,̶ ̶l̶i̶n̶k̶a̶g̶e̶-̶d̶i̶s̶a̶g̶r̶e̶e̶m̶e̶n̶t̶
//as @EricPostpischil mentioned in the comment
//it is well-defined in 6.2.2
案例5.
int a;
long a; //6.7.2 UB incompatible types
案例6.
int a;
const int a; //6.7.2/6.7.3 incompatible types, different qualifiers
案例7.
enum{
a
};
enum{
a //UB, why?
};
案例8.
enum {
a
};
const unsigned char a; //UB, why?
案例1-4
标准中的解释清晰明确。
6.2.2(p7):
If, within a translation unit, the same identifier appears with both
internal and external linkage, the behavior is undefined.
案例5
在 6.2.7(p1):
部分进行了解释
If, within a translation unit, the same identifier appears with both
internal and external linkage, the behavior is undefined.
和6.7(p4):
All declarations in the same scope that refer to the same object or
function shall specify compatible types.
案例6
由6.7.3(p10)解释：
For two qualified types to be compatible, both shall have the
identically qualified version of a compatible type
案例7-8。
不清楚。我没有在标准中找到与它们相关的任何正式参考。 6.2.7(p1) 状态：
For two enumerations, corresponding members shall have the same
values.
案例 7 满足该要求。
所以我没有发现任何问题。
我没有发现任何与案例 8 明确相关的内容，所以好像它没有在标准中定义，它应该是 UB。
你能帮忙在案例7和的标准中找到解释吗案例8?
案例7
由6.7.2.3第1、4、5段（第137页）解释（重点是我的）
1 A specific type shall have its content defined at most once.
4 All declarations of structure, union, or enumerated types that
have the same scope and use the same tag declare the same type.
Irrespective of whether there is a tag or what other declarations of
the type are in the same translation unit, the type is incomplete
[footnote 129)] until immediately after the closing brace of the list
defining the content, and complete thereafter.
5 Two declarations of structure, union, or enumerated types which
are in different scopes or use different tags declare distinct types.
Each declaration of a structure, union, or
enumerated type which does not include a tag declares a distinct type.
因此，相同类型枚举的示例 [如果不是第 1 段] 就像
enum TagNameA
{
a
};
enum TagNameA
{
a
};
案例8
由6.7.2.2第3段（第136页）解释（重点是我的）
The identifiers in an enumerator list are declared as constants that
have type int and may appear wherever such are permitted [footnote:
127)]
...
[footnote 127)] Thus, the identifiers of enumeration constants
declared in the same scope shall all be distinct from each other and
from other identifiers declared in ordinary declarators.
案例 8
const unsigned char a;
是a的普通声明符，与枚举常量标识符不同 =37=] a.
案例 8
enum {
a
};
const unsigned char a; //UB, why?
这不是UB。这是语义错误。 UB 可能只在运行时发生。
重复标识符 'a'。考虑
int b = a; //which a?
案例 7
enum{
a
};
enum{
a //UB, why?
};
这不是UB。这是语义错误。 UB 可能只在运行时发生。
重复标识符 'a'。考虑
int b = a; //which a?
这是一个关于 ISO C 的语言律师问题。
我想了解标准中是如何定义声明的。我使用 N1570。考虑以下情况：
案例一.
int a;
extern int a; //compatible types, external linkage, well-defined behavior
案例二.
extern int a;
int a; //well-defined behavior, external linkage, well-defined behavior
案例三.
int a;
static int a; //6.2.2/6.9.2UB, linkage-disagreement
案例4.
static int a;
extern int a; //6̶.̶2̶.̶2̶/̶6̶.̶9̶.̶2̶ ̶U̶B̶,̶ ̶l̶i̶n̶k̶a̶g̶e̶-̶d̶i̶s̶a̶g̶r̶e̶e̶m̶e̶n̶t̶
//as @EricPostpischil mentioned in the comment
//it is well-defined in 6.2.2
案例5.
int a;
long a; //6.7.2 UB incompatible types
案例6.
int a;
const int a; //6.7.2/6.7.3 incompatible types, different qualifiers
案例7.
enum{
a
};
enum{
a //UB, why?
};
案例8.
enum {
a
};
const unsigned char a; //UB, why?
案例1-4
标准中的解释清晰明确。
6.2.2(p7):
If, within a translation unit, the same identifier appears with both internal and external linkage, the behavior is undefined.
案例5
在 6.2.7(p1):
If, within a translation unit, the same identifier appears with both internal and external linkage, the behavior is undefined.
和6.7(p4):
All declarations in the same scope that refer to the same object or function shall specify compatible types.
案例6
由6.7.3(p10)解释：
For two qualified types to be compatible, both shall have the identically qualified version of a compatible type
案例7-8。
不清楚。我没有在标准中找到与它们相关的任何正式参考。 6.2.7(p1) 状态：
For two enumerations, corresponding members shall have the same values.
案例 7 满足该要求。
所以我没有发现任何问题。
我没有发现任何与案例 8 明确相关的内容，所以好像它没有在标准中定义，它应该是 UB。
你能帮忙在案例7和的标准中找到解释吗案例8?
案例7
由6.7.2.3第1、4、5段（第137页）解释（重点是我的）
1 A specific type shall have its content defined at most once.
4 All declarations of structure, union, or enumerated types that have the same scope and use the same tag declare the same type. Irrespective of whether there is a tag or what other declarations of the type are in the same translation unit, the type is incomplete [footnote 129)] until immediately after the closing brace of the list defining the content, and complete thereafter.
5 Two declarations of structure, union, or enumerated types which are in different scopes or use different tags declare distinct types. Each declaration of a structure, union, or enumerated type which does not include a tag declares a distinct type.
因此，相同类型枚举的示例 [如果不是第 1 段] 就像
enum TagNameA
{
a
};
enum TagNameA
{
a
};
案例8 由6.7.2.2第3段（第136页）解释（重点是我的）
The identifiers in an enumerator list are declared as constants that have type int and may appear wherever such are permitted [footnote: 127)]
...
[footnote 127)] Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from each other and from other identifiers declared in ordinary declarators.
案例 8
const unsigned char a;
是a的普通声明符，与枚举常量标识符不同 =37=] a.
案例 8
enum {
a
};
const unsigned char a; //UB, why?
这不是UB。这是语义错误。 UB 可能只在运行时发生。
重复标识符 'a'。考虑
int b = a; //which a?
案例 7
enum{
a
};
enum{
a //UB, why?
};
这不是UB。这是语义错误。 UB 可能只在运行时发生。
重复标识符 'a'。考虑
int b = a; //which a?