C / C++ / MFC

Dave Schumann wrote:

So why can't B - which IS AN A - access the value member of another A?

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Maximilien wrote:

all members in structs should be public

Dave Schumann wrote:

No it's not.

Dave Schumann wrote:

Changing these to "classes" with public: at the beginning has no effect (I've tried it)

struct A
{
    A* partner;
 
    void doodah()
    { ++partner->value; } //this is legal
    int value; 
};

class A
{
public:
    A* partner;
 
    void doodah()
    { ++partner->value; } //this is legal
    int value;
};

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Dave Schumann wrote:

I declared "protected:" for a reason, not because I like having things not compile. This is a toy version of a much larger problem. I can't stand posters who post 20 pages of code so I figured I'd boil the issue down. In fact in my case the issue is accessing a *function*...and there's virtual stuff and blah blah blah. Now you're getting bored, appropriately. None of that is relevant to the compiler error which I can't understand.

Zac Howland wrote:

I will only mention that almost always, protected should be replaced by private.

toxcct wrote:

maybe, but here, the protected member is accessed by a children... so, putting it private will cause a new problem in his code.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Dave Schumann wrote:

It's not complaining about accessing "partner"

class A
{
public:
	A* partner;

	void doodah()	{ ++partner->value; }
	int getValue() const		{ return value; }
	void setValue(int newValue)	{ value = newValue; }
protected:
	int value;
};

class B: public A
{
public:
	void foobar()	{ partner->setValue(partner->getValue() + 2); }
};

Dave Schumann wrote:

You've provided public accessors to "value". If I wanted value to be accessible publicly, I'd just make it public.

Dave Schumann wrote:

I'm not putting "protected" in just to make life hard. I actually don't want any outside classes modifying "value". If you make "setValue" protected above - which is the whole point - then you've violated the restrictions I want on "value".

Zac Howland wrote:

Why do you have a pointer to A as a member of class A? From experience, every single time I've seen that type of code, it has been due to poor design

class MyJunk
{
public:
	void DoSomething() {}
private:
	int _Data;
};

std::list<MyJunk> myJunkList;

Dave Schumann wrote:

Except when forming a pointer to member (expr.unary.op), the access must be through a pointer to, reference to, or object of the derived class itself (or any class derived from that class)