来源: http://dev.firnow.com/course/3_program/c++/cppsl/2008619/126863.html

MSDN:
compiler warning (level 1) C4482
warning description:

使用了非标准扩展: 限定名中使用了枚举“enum”
当引用类型内的枚举时，无需指定枚举的名称。
文件范围的枚举定义相当于常量，也不需要限定名。

example: C4482(MS Visual Studio)

// C4482.cpp

// compile with: /c /W1

struct S {
   enum E { a };
};

int i = S::E::a; // C4482

int j = S::a; // OK

NOTE:
warring C4482: nonstandard extension used: enum **** used in qualified name

enumeration:
1. Standard C++ does not allow enumeration names to be used as scopes (GCC: error)
Visual C++ is half-hearted on the matter. (warrning)
2. C# support enumeration names as scopes.

Workaround: (for MS Visual Stdio)
if you want to get rid of those obnoxious error message and you’re using MS Visual Studio, encompass your statement in #pragma directives. For example,

That tells the compiler not to report the C4482 warning for the code within the block.
You are essentially saying to the compiler, “Yes, I’m doing this intentionally. I know it’s not comply with the standard, but I want it done anyway. So build my project and quit your whining!”