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Call-By-Value versus Call-By-Refference

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Call-By-Value versus Call-By-Refference

 
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Aug 24th, 2009
Could Someone tell me whats the diffrence between call-by-value with call-by-refference?
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Re: Call-By-Value versus Call-By-Refference

 
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Aug 24th, 2009
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Originally Posted by hket89 View Post
Could Someone tell me whats the diffrence between call-by-value with call-by-refference?
Hard time using a search engine?
http://www.lmgtfy.com/?q=pass+by+value+or+reference
Last edited by tux4life; Aug 24th, 2009 at 11:00 am.
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Re: Call-By-Value versus Call-By-Refference

 
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Aug 24th, 2009
In general, passing by value means that a copy of variable is made with the same value and passing by reference means the variable object itself is passed. You can change the value all you want with pass by value, but the original object is not changed. With pass by reference any changes to the passed variable also change the original. C does not support passing by reference, but you can fake it with pointers:
c Syntax (Toggle Plain Text) 
  1. #include <stdio.h>
  2.  
  3. void CallByValue(int x)
  4. {
  5.     x = 123;
  6. }
  7.  
  8. void CallByFakeReference(int* x)
  9. {
  10.     *x = 123;
  11. }
  12.  
  13. int main()
  14. {
  15.     int x = 0;
  16.  
  17.     printf("Before CallByValue: %d\n", x);
  18.     CallByValue(x);
  19.     printf("After CallByValue: %d\n\n", x);
  20.  
  21.     printf("Before CallByFakeReference: %d\n", x);
  22.     CallByFakeReference(&x);
  23.     printf("After CallByFakeReference: %d\n", x);
  24.  
  25.     return 0;
  26. }
Faking call by reference is done by passing the address of an object and then accessing the value through indirection. That way you can get to the original object and make changes, but the address is still passed by value.
Last edited by Tom Gunn; Aug 24th, 2009 at 10:56 am.
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Re: Call-By-Value versus Call-By-Refference

 
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Aug 24th, 2009
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Originally Posted by tux4life View Post
Hard time using a search engine?
come on, man. that's a legitimate question to ask.
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Re: Call-By-Value versus Call-By-Refference

 
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Aug 24th, 2009
A side note : one of the main reason call by reference was created is
because passing a class object by value is expensive.

You can think of Pass by reference like a pointer in disguise. 
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1) What word becomes shorter if you add a letter to it? [ Solved by : niek_e ]
2) What does this sequence  equal to :  (.5u - .5a)(.5u-.5b)(.5u-.5c) ...
3) What is the 123456789 prime numer?
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Re: Call-By-Value versus Call-By-Refference

 
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Aug 25th, 2009
What is the purpose of using call by value and call by reference?
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Re: Call-By-Value versus Call-By-Refference

 
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Aug 25th, 2009
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Originally Posted by hket89 View Post
What is the purpose of using call by value and call by reference?
Your question revealed that perhaps you are not understanding what it has been explained so far.
There's not such a thing as call by reference in The C language. Everything done is done by coping values around.
It is like a World where credit hasn't been invented. Anything you buy you need to pay with cash. The bigger the purchase, the more cash you have to carry around, the more cash you carry the more effort you have to make.
Pointers are like checks. Now you don't carry money around, but rather the small weight of a check book. And with a simple check you can provide the value of a much heavy and cumbersome pile of cash.

On the other hand. Call by reference in some other languages is like paying with Credit Cards.
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Re: Call-By-Value versus Call-By-Refference

 
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Aug 25th, 2009
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Originally Posted by hket89 View Post
What is the purpose of using call by value and call by reference?
Again :

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A side note : one of the main reason call by reference was created is
because passing a class object by value is expensive.

You can think of Pass by reference like a pointer in disguise.
Pass by reference is a pointer under the hood. 
I give up! 
1) What word becomes shorter if you add a letter to it? [ Solved by : niek_e ]
2) What does this sequence  equal to :  (.5u - .5a)(.5u-.5b)(.5u-.5c) ...
3) What is the 123456789 prime numer?
Ask4Answer
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Re: Call-By-Value versus Call-By-Refference

 
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  #9
Aug 25th, 2009
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Pass by reference is a pointer under the hood.
There is no hood to look under. C does not have pass by reference, only pass by value. Pass by reference is faked in C by passing pointers by value and using indirection to get to the object.

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A side note : one of the main reason call by reference was created is
because passing a class object by value is expensive.

You can think of Pass by reference like a pointer in disguise.
I think you are talking about C++, but even in C++, the main reason references are part of the language is to support operator overloading. They are also a convenient way to make output parameters, but that is a side effect of the original goal.
Last edited by Tom Gunn; Aug 25th, 2009 at 3:19 pm.
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Oct 14th, 2009
thanx
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