C 14: enumeration previously declared with fixed underlying type: different behavior between compil-CodePudding

Sample code:

enum E : char;
enum E;

Invocations:

$ g   -std=c  14 -pedantic -Wall -Wextra -c
<nothing>

$ clang   -std=c  14 -pedantic -Wall -Wextra -c
<source>:2:6: error: enumeration previously declared with fixed underlying type

$ icc -std=c  14 -pedantic -Wall -Wextra -c
<nothing>

$ cl /std:c  14 /Za
<source>(2): error C3432: 'E': a forward declaration of an unscoped enumeration must have an underlying type
<source>(2): error C3433: 'E': all declarations of an enumeration must have the same underlying type, was 'char' now 'int'

Is this code well-formed?

What the standard says?

CodePudding user response：

From [dcl.enum]/3:

An unscoped enumeration shall not be later redeclared as scoped and each redeclaration shall include an enum-base specifying the same underlying type as in the original declaration.

Emphasis added. Clang is correct.