constructor and its uses

Hi Guys,

If we have a class as:

Code:

---

class student
{

 int roll_no;
 string name;
 char student_id;

public:

student(string=null,int=0,char=null);


};

---

I wanted to know that can we initialize string using constructor?
Can we initialize string with a "null"?

You can initialize the string in many ways, as an example (using an int instead of a string) consider:

Code:

---

class bar
{
    int value;
public:
    bar(int val = 42) : value(val)
    {
    }
};

---

Now I can initialize an object of this particular class in a couple different ways:

Code:

---

bar foo1;      // Creates an object foo1 with value initialized to 42
bar foo2(5);  // Creates an object foo2 with value initialized to 5
bar foo3 = 7;  // Creates an object foo3 with value initialized to 7

---

No. A string has a default value of "" (nothing), which "is" NULL for a string. NULL itself is meant for pointer memory values however, in which it is 0x0 (nothing)

A class constructor can be used to initialise your member variables as you said, by using the name of the class itself as a function with no type or return value.

Code:

---

public:
  student() { name = "Eric"; roll_no = 25; student_id = "99320002"; }
  ~student(){}

---

A deconstructor is is called if the class goes out of scope (or is delete'd as a pointer (a constructor is called when new is used or a non-pointer init is called)). What you're trying to do is called an initialisation list. And that's not how it's done.

Code:

---

student() : name(""), roll_no(25), student_id("99320002") {}

---

Quote:

---

Originally Posted by Rodaxoleaux

Code:

---

student() : name(""), roll_no(25), student_id("99320002") {}

---

---

Personally, I'd get rid of the red part, seeing as the default constructor of std::string creates an empty string anyway.

EDIT: Or better yet, give student a c'tor that takes arguments and initializes its members to proper values to begin with.

Quote:

---

Originally Posted by Rodaxoleaux

A deconstructor is is called if the class goes out of scope

---

A destructor is is called if the class goes out of scope.
FTFY!

Note that having an empty non-virtual destructor is not desireable. If you destructor does not need to be marked virtual and has no work to do, then it should be deleted.

Thanks for the corrections.
Yeah, I didn't sleep last night give me a break o.e

Hi

Thanks for all your reply,

so in the class of student:

--------------------------------------------------------------------------------------------------

Code:

---


class student

{ 

int roll_no; 
string name; 
char student_id; 

public: 

student(string,int,char);    //constructor with parameters/

};

---

----------------------------------------------------------------------

Can we initialize the data members of a class just by using their data types?

Quote:

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Originally Posted by student111

Can we initialize the data members of a class just by using their data types?

---

You said thanks for the replies as if you read them, but your new code suggests that you didn't look or take into account a word that was typed.

Quote:

---

Originally Posted by student111

Can we initialize the data members of a class just by using their data types?

---

No.

However, the string in your class is initialised by itself without you doing anything.

Quote:

---

Originally Posted by student111

Can we initialize the data members of a class just by using their data types?

---

What do you mean by using their data type? The example you provided doesn't have much to do with initialization. The line that you bolded is the constructor portion of a class declaration. The most that has to do with initialization is the fact that the compiler will check the types of what you pass in with the types of the parameters to see if they match.

The updated code seem to reflect the inability to consume the material that has been presented so far.
I still see a single character instead of a string.
I still see the inability to add names to the parameters.
I still see the inability to understand how to initialize members.
And there is probably more...

Re-read all those posts you've been given. Consume their contents. Correct your code and ask new questions. If there is something specific about what you've been told so far that you fail to understand completely, then ask specific questions about that.