为什么C++11 'auto‘关键字对静态成员无效？

Question

class Foo {
 public:
  static const char *constant_string;
};

auto Foo::constant_string = "foo";

int main(void) {
};

编译: gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3如下：

gcc -std=c++0x ./foo.cc 
./foo.cc:6:11: error: conflicting declaration ‘auto Foo::constant_string’
./foo.cc:3:22: error: ‘Foo::constant_string’ has a previous declaration as ‘const char* Foo::constant_string’
./foo.cc:6:11: error: declaration of ‘const char* Foo::constant_string’ outside of class is not definition [-fpermissive]

这是auto关键字的预期行为，还是gcc+中的错误

Answer 1

Visual C++接受

decltype(Foo::constant_string) Foo::constant_string = "foo";