compiler-error-c2248.md

description	title	ms.date	f1_keywords	helpviewer_keywords	ms.assetid
Learn more about: Compiler Error C2248	Compiler Error C2248	09/27/2022	C2248	C2248	7a3ba0e8-d3b9-4bb9-95db-81ef17e31d23

Compiler Error C2248

'member': can't access 'access_level' member declared in class 'class'

Remarks

Members of a derived class can't access private members of a base class. You can't access private or protected members of class instances.

Example

The following sample generates C2248 when private or protected members of a class are accessed from outside the class. To fix this issue, don't access these members directly outside the class. Use public member data and member functions to interact with the class.

// C2248_access.cpp
// compile with: cl /EHsc /W4 C2248_access.cpp
#include <stdio.h>

class X {
public:
    int  m_publicMember;
    void setPrivateMember( int i ) {
        m_privateMember = i;
        printf_s("\n%d", m_privateMember);
    }
protected:
    int  m_protectedMember;

private:
    int  m_privateMember;
} x;

int main() {
    x.m_publicMember = 4;
    printf_s("\n%d", x.m_publicMember);
    x.m_protectedMember = 2; // C2248 m_protectedMember is protected
    x.m_privateMember = 3;   // C2248  m_privMemb is private
    x.setPrivateMember(0);   // OK uses public access function
}

Another conformance issue that exposes C2248 is the use of template friends and specialization. To fix this issue, declare friend function templates by using either an empty template parameter list <> or specific template parameters.

// C2248_template.cpp
// compile with: cl /EHsc /W4 C2248_template.cpp
template<class T>
void f(T t) {
    t.i;   // C2248
}

struct S {
private:
    int i;

public:
    S() {}
    friend void f(S);   // refer to the non-template function void f(S)
    // To fix, comment out the previous line and
    // uncomment the following line.
    // friend void f<S>(S);
};

int main() {
    S s;
    f<S>(s);
}

Here's another conformance issue that exposes C2248: You attempt to declare a friend of a class, but the class isn't visible to the friend declaration in the scope of the class. To fix this issue, grant friendship to the enclosing class.

// C2248_enclose.cpp
// compile with: cl /W4 /c C2248_enclose.cpp
class T {
    class S {
        class E {};
    };
    friend class S::E;   // C2248
};

class A {
    class S {
        class E {};
        friend class A;  // grant friendship to enclosing class
    };
    friend class S::E;   // OK
};