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pointer versus reference in the argument

Posted on 2016-08-29
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Last Modified: 2016-09-19
Hi

I have noticed that certain function take a reference where others take a pointer in the argument of a function.


eg: A::A(X& x)
versus
     A::A(X* x)

what are the pros and cons of both? what would be the advantage of doing the reference over the pointer ?

thanks
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Question by:LuckyLucks
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7 Comments
 
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Expert Comment

by:Subrat (C++ windows/Linux)
ID: 41775713
Reference is treated as constant pointer and can automatically dereferenced.

In your ex first one is copy constructor where as second is passing address of an object belonging to class A to class A's one arg constructor.

Pointer can be null but reference can't. If you want to pass null object to a function,  use pointer. In caller side,      by looking the call you can say it is pass by address/pointer or not.  But can't detect reference,  as it is also looking like call by value.
Ex  
void fun(a) ; // it can be pass by value or reference. Only can be determined by looking the header or source.
void fun(&a) ; // it is pointer no doubt

Reference to const also accepts temporary
void f(const T& t)
f(T(a, b, c)) ;
But pointer can't as you can't take address of temporary.
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Expert Comment

by:phoffric
ID: 41775742
>>  copy constructor
Could you clarify why you say it is a  copy constructor
http://en.cppreference.com/w/cpp/language/copy_constructor

When you provide a list of buzz words without explaining what they are, then it is a good idea to provide a link that explains what it is.

>> as second is passing address of an object belonging to class A to class A's one arg constructor.
Then what is X?
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Expert Comment

by:Subrat (C++ windows/Linux)
ID: 41775817
I m sorry,  my overlook.  It is constructor accepting reference of type X
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Accepted Solution

by:
pepr earned 500 total points (awarded by participants)
ID: 41775861
I personally prefer references wherever possible. It was not possible in the past because references were not available in the old C++.

With references, syntax of the source code is simpler. References are less error prone than pointers (because you have to care more in advance -- when writing the source). The source code is more readable. If the code was once a block of code that used the statically allocated object behind the identifier, then moving that code to the function body (during refactoring) is easier (less error prone) than rewriting to the same code that uses pointers.

There is indirect access hidden inside (that is the automatic dereference of the address), so still may be careful when efficiency is important -- but it is the same compared to to using a pointer instead.

I prefer to add const modifier whenever it makes sense. It is a bit more of work at the beginning, but you will get used to, and the more strict approach finally leads to more flexibility (possibly difficult to explain).
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by:LuckyLucks
ID: 41777342
This is not correct:
"Reference is treated as constant pointer and can automatically dereferenced."


A reference is a de-referenced immutable(const) pointer. It's not can be, it already is. Perhaps you meant the same thing but the way it was written suggested a different meaning.
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Expert Comment

by:phoffric
ID: 41777532
@Subrat
>> Reference is treated as constant pointer and can automatically dereferenced."

When you make statements like this using easy language, then to make your point, I suggest that you pose a concrete code snippet with comments to illustrate your statement.
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