BUG: /Za Compiler Option Causes C2248 Compiler Error

ID: Q243351

The information in this article applies to:

The C/C++ Compiler (CL.EXE), included with:
- Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

When compiling code with the /Za compiler option (Disable Microsoft Language extensions) you may get the following error:

error C2248: 'member' : cannot access private 'member' declared in class 'class'

For details, please look in the "More Information" section.

CAUSE

The compiler is unable to defer the access checking until it determines the use of a private member as a return type. The C++ Standard, Section 11 Paragraph 5 states the following:

"The access control for names used in the definition of a class member that appears outside of the member's class definition is done as if the entire member definition appeared in the scope of the member's class. In particular, access controls apply as usual to member names accessed as part of a function return type, even though it is not possible to determine the access privileges of that use without first parsing the rest of the function declarator."

RESOLUTION

There are two workarounds for this problem.

Define the private function within the class definition itself.

Define a public typedef for the return type.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

Steps to Reproduce Behavior

To reproduce the problem, compile the following piece of code with the /Za option.


//compiler options : cl /Za

// #define WORKAROUND 
// Uncomment the above line for workaround 2.

class A
{
private :
	struct inner {};
	inner PrivFunc();

public:
    A(){}

#ifdef WORKAROUND
		typedef inner INNER; 
#endif
		

};

#ifndef WORKAROUND
A::inner A::PrivFunc()
{
	return inner();
}
#else
A::INNER A::PrivFunc()
{
	return INNER();
}
#endif

void main(void)
{

}

The use of A::inner is well formed here because A::inner is a member of class A. This implies that the access checking for the first use of A::inner must be deferred until it is determined that this use of A::inner is as the return type of a member of class A.

Additional query words:

Keywords : kbCompiler kbCPPonly kbVC600 kbVC600bug
Version : winnt:6.0
Platform : winnt
Issue type : kbbug