C++ private modifier ignored on nested anonymous struct

问题

The following sample code compiles just fine in Visual C++:

class Test {
private:
    struct {
        struct {
            int privateData;
        };
    };
};

int main(int, char **)
{
    Test test;
    test.privateData = 0;
    return 0;
}

But why? I'd expect a compiler error because the privateData member should be inaccessible to the function main, since it's supposed to be private like its container's container. I know that nameless structs are not part of official C++, but this design is asinine.

By the way I've also tried to change private into protected and struct into union: it looks like the compiler refuses to honor access modifiers on anonymous structs and unions that are nested inside another anonymous struct or union.

Can someone explain this feature?

回答1:

Yes, it is a bug. Microsoft acknowledged it is, the feedback report is here.

Right now the bug is in "will not fix" status and it is unclear when (if ever) it will be addressed. There is a somewhat odd workaround for it, the IntelliSense parser built into Visual Studio, written by the Edison Design Group, does complain about it. You get the red squiggles and the message:

Error: member "Test.privateData" (declared at line 10) is inaccessible

来源：https://stackoverflow.com/questions/14187647/c-private-modifier-ignored-on-nested-anonymous-struct