Tuesday, December 16, 2008

C++ inheritance - public, private, protected

Inheritance in C++ could be public, private, or public. It could be confusing for a beginner to find out accessibility of members and objects of these classes. Though public inheritance is mostly used, especially if there are virtual functions in the base class, other two types of inheritance have their uses as well. Here's an example program to make it clear how the 3 of them work i.e. public inheritance, private inheritance, and protected inheritance.



#include

class B{
char a;

public:
char b;

protected:
char c;
};

// public inheritance

class D:public B{

// private members of B can't be accessed
//can access public and protected members of B

char d;

public:

void f(){
//can't do this
// d = a;

d = b; // works
d = c; // works
}

// class D has the following additional members inherited from B
// public: char b
// and
// protected: char c
// this means that any class derived from D can access both b and c
// b is accessible by objects of derived class, c is not (#1)
};

// private inheritance

class E:private B{

// private members of B can't be accessed...
// can access public and protected members of B

char d;

public:
void f(){
//can't do this
// d = a;
d = b; // works
d = c; // works
}


// class E has the following additional data members inherited from B
// private:char b
// and
// private: char c
// this means that any class derived from E can't access any of the above derived data
// members, nor are they accessible to objects of derived class, public functions
// though are accessible to objects of this class (#2)

};

// protected inheritance

class F:protected B{

// private members of B can't be accessed in this class as above, so
// can access public and protected members of B

char d;

public:

void f(){
//can't do this
// d = a;
d = b; // works
d = c; // works
}

// class F has following additional members inherited from B
// protected:char b
// and
// protected: char c
// this means that any class derived from F can access
// the above members, but they can't be accessed from
// derived class objects (#3)
};

class DF: public F{
char d;

public:
void g(){
d = b; // works from #3 above
d = c; // works from #3
}
};



int main(){

char i;

B b;
D d;
E e;
F f;

// these won't work by definition
// b.c = i;
// b.a = i;


// for object d of publicly derived class
// this works from (#1)
d.b = i;
// this won't work from (#1)
// d.c = i;


// for object e of privately derived class
// these won't work from (#2)
// e.b = i;
// e.c = i;


// for object f of protected-ly derived class
// these won't work from (#3)
// f.b = i;
// f.c = i;

return 0;
}

Sunday, October 26, 2008

Small company or MNC

One of my friends has recently graduated and is in a dilemma on which among the two offers to accept. An offer he has is from a multi-billion, multi-thousand-employees product MNC where he would be using C language and Unix at work that is about debugging one of the company products. The other offer is from a small EDA company where he would be using C++ and Windows as a developer of EDA tools for engineers. The smaller company has less than 50 people on roll. The CEO himself interviewed my friend and has suggested that the friend would have more opportunities to learn and grow in a smaller company like his one.

On the other hand, the big MNC's salary offer is more than twice that of the smaller company's.

Friend is in a dilemma and is seeking my advice. Which company should he join?

Friday, October 24, 2008

pointer pitfall

Some C pointer fundamentals manage to fox even seasoned programmers.
For example, what is wrong with the following piece of code:

func() {

char *c;
c = "this is a string.";
*c = 'T';
printf("%s", c);
}


The code tries to capitalize the first letter of the string. It looks correct at first glance, but is not. It might even compile without any error, but will throw out an error when run.