Why Does The destructor destroy the original object??

This is a discussion on Why Does The destructor destroy the original object?? within the C++ Programming forums, part of the General Programming Boards category; Ok is this one now correct?? Code: class str { char *s; public: str(){} ~str() { delete []s; } str(str ...

  1. #16
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    Ok is this one now correct??

    Code:
    class str
    {
    	char *s;
    	public:
    		str(){}
    		~str()
    		{
    			delete []s;
    		}
    		str(str &p)
    		{
    			s=new char[strlen(p.s)+1];
    			strcpy(s,p.s);
    		}
    		void getdata(char*);
    		void putdata();
    		friend int xstrlen(str);
    
    };

  2. #17
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    Looks good to me.

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  3. #18
    C++まいる!Cをこわせ! Elysia's Avatar
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    Yep, much better. You can try to use more descriptive names for your variables and rename getdata/putdata to more appropriate names, too, if you want something extra to do.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
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  4. #19
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    Ok last and final question..is what i am doing in this function is that i am allocating a new memory space for my string so that the "string" and *s point to different memory location so when the destructor frees the memory the original object doesn't get destroyed?
    is this correct what i have understood?

  5. #20
    C++まいる!Cをこわせ! Elysia's Avatar
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    Yes, you are correct. You're making a copy of the data, so each class has its own instance of the string.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  6. #21
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    Ok this is deep copying. Now what is shallow copying?that one which is there in getdata???right??

    but in that also i allocated the memory so how come *s and "string" both point to the same location?

  7. #22
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    Quote Originally Posted by chottachatri View Post
    Ok this is deep copying. Now what is shallow copying?that one which is there in getdata???right??
    Shallow copy means you're just copying pointers over, while deep copy means you copy the data pointed to by the pointers, as well.

    but in that also i allocated the memory so how come *s and "string" both point to the same location?
    Huh? There is no "string." You forgot to give them a descriptive name.


    Oh, I also see something else. Always put names for arguments in class definitions, as well.
    For example:
    void getdata(char* pStr);
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  8. #23
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    You mean the same 2 lines i have written in getdata and in copy constructor but still 1 is deep copy and 1 is shallow copy???

    You mean the difference is just of the copy constructor??is it the root?

  9. #24
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    Quote Originally Posted by chottachatri View Post
    You mean the same 2 lines i have written in getdata and in copy constructor but still 1 is deep copy and 1 is shallow copy???

    You mean the difference is just of the copy constructor??is it the root?
    deep and shallow copying refers to how you copy an object. getdata() is not copying an object, is it?

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  10. #25
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by chottachatri View Post
    You mean the same 2 lines i have written in getdata and in copy constructor but still 1 is deep copy and 1 is shallow copy???
    No, both are deep copy. Look again.

    You mean the difference is just of the copy constructor??is it the root?
    That makes no sense...
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  11. #26
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    If both are deep copy then Elysia how come are they(object's pointer and the string) pointing to the same memory location?

  12. #27
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    They won't, unless you do something wrong.
    Remember that there are two instances of the objects. Both of these two will not pointer to the same memory location, since you allocated more memory and copied the data over.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  13. #28
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    Now you'll also need to overload the assignment operator. Otherwise you'll have the original problem when you do this:
    Code:
    str a, b;
    a = b;
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  14. #29
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    Quote Originally Posted by chottachatri View Post
    If both are deep copy then Elysia how come are they(object's pointer and the string) pointing to the same memory location?
    Huh?

    if you call the putData() function, you get a copy of the string [which your existing code is not freeing], and the copy constructor creates a copy of the string. So neither is pointing to the string in the original object.

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    Please don't PM me for help - and no, I don't do help over instant messengers.

  15. #30
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    OK this time i got it for sure!! you mean to say when we do call by value for objects(xstrlen..in this case) the default copy constructor get's called and it copies only the address of the original object and doesn't allocate the memory?right??

    and now what is anon talking about?why should be overload the assignment operator??the assignment operator is already overloaded isnt it??and i tried B=A as well as A=B but i am getting the right output only?

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