What is the default access modifier for class members and member functions in a class?

Class default access modifier

Access modifier is the rule on how an attribute of Class can be accessed from outside the scope of the class. Basically it defines how the outside world can access the member attributes. We are discussing the default access rules of a C++ class. The default access modifier for class member variable and member functions is "private" in C++ class. This means if we do not provide any access modifier then by default the members are considered as private.

Private members are the class members either data members of member functions those are hidden from the outside world. The private members implement the concept of data hiding in the object oriented programming.

Class default access (private)

class student
{
  int m_Member1;
   student();
   ~student();
};

student::student()
{
}

student::~student()
{
}

int main( int argc, char * argv[])
{
   student * s1 ;
  s1 = new  student();
  s1->m_Member1 = 0;
  delete s1;
}

Compilation

The above program can not compile since all default access modifier are private. Let's see what all compilation error we will be getting.

$ g++ class.cpp
class.cpp:19:13: error: calling a private constructor of class 'student'
  s1 = new  student();
            ^
class.cpp:4:4: note: implicitly declared private here
   student();
   ^
class.cpp:20:7: error: 'm_Member1' is a private member of 'student'
  s1->m_Member1 = 0;
      ^
class.cpp:3:7: note: implicitly declared private here
  int m_Member1;
      ^
class.cpp:21:10: error: calling a private destructor of class 'student'
  delete s1;
         ^
class.cpp:5:4: note: implicitly declared private here
   ~student();
   ^
3 errors generated.
$

Class default access override with "public"

Having "public" access can pass the compilation.

class student
{
public:
  int m_Member1;
   student();
   ~student();
};

student::student()
{
}

student::~student()
{
}

int main( int argc, char * argv[])
{
   student * s1 ;
  s1 = new  student();
  s1->m_Member1 = 0;
  delete s1;
}

Sctucture default access modifier

Now we know the default access modifier of C++ class. Is this same rule applicable for C++ structures? The answer is No, structure follows the concept of C with no object oriented concept by default. Thus members can be accessed outside by default until access modifiers are made private.

Know more about this. See also: What is the default access modifier for structure members and member functions in c++?

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