What does ** mean in C++?

Question

For example:

bool insertInFront( IntElement **head, int data ){
    IntElement *newElem = new IntElement;
    if ( !newElem ) return false;

    newElen->data = data;
    *head = newElem; // Correctly updates head
    return true;
}

I am new to C++, coming from Java. I get the * for indirection syntax, but ** is not listed on this page: http://en.wikipedia.org/wiki/Operators_in_C_and_C++#Member_and_pointer_operators

I found this example on page 28 of Programming Interviews Exposed

Update

I realize that this question is naive, and I probably could have found an answer through other means. Obviously, I am new to the language. Still, asking "What does ** mean?" is not well supported online for someone who does not know that ** is a pointer operation. There are very few relevant results when searching C ** syntax or C++ ** meaning. Additionally, using ctrl + f to search ** in the wiki page above, and other documentation, doesn't return any matches at all.

I just wanted to clarify, from a beginner's perspective, that this question is hard to distinguish from the duplicates. Of course, the answer is the same :-) Thank you for the help.

This question appears to be off-topic because it doesn't demonstrate minimal understanding of the problem being solved. — Maroun, May 08 '14 at 09:35
Yes, it is listed on that page, as the case when `a` is `*A` for some `A`. — Angew is no longer proud of SO, May 08 '14 at 09:36
@rubenvb Oh I thought you did it on purpose. The link you posted points to a link, that points to the post. — John Bupit, May 08 '14 at 11:47
@John oh wow. And here I was just thinking I marked a question as a duplicate `:-P`. Nice going me :-) — rubenvb, May 08 '14 at 11:50

score 10 · Accepted Answer · answered May 08 '14 at 09:32

10

There is no specific ** operator in C++, instead it's two separate asterisks, and asterisks in a declaration denotes pointer declaration.

So in the declaration

IntElement **head

the argument head is declared to be a pointer to a pointer to IntElement.

answered May 08 '14 at 09:32

Some programmer dude

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Congrats for the new avatar. – Maroun May 08 '14 at 09:35
Well.. I need a congratulations too, just got a new job ;) – Maroun May 08 '14 at 09:39
1

@MarounMaroun Then congrats to you too! :) – Some programmer dude May 08 '14 at 09:39

score 2 · Answer 2 · answered May 08 '14 at 09:40

Its meaning:

int a;                // integer
int *ptrA = &a        // pointer to a integer
int **PtrPtrA = &ptrA // point to pointer to a integer

How can it be used:

void function_nochange(int *pA  ) {   pA   = &b;  } 
void function_change  (int **ppA) {   *ppA = &b;  } 

int a;
int b;
void test()
{
  int *ptrA = &a

  function_nochange(ptrA)
  // here ptrA still point to int a since ptrA was copied

  function_change(&ptrA)
  // here ptrA point to int b since ptrA was passed as pointer 
}

snehal · Answer 3 · 2014-05-08T12:58:06.113

1

**VariableName means pointer to pointer(a chain of pointers) in C++

You can find good tutorials here :

http://www.tutorialspoint.com/cplusplus/cpp_pointer_to_pointer.htm

http://www.codeproject.com/Articles/4894/Pointer-to-Pointer-and-Reference-to-Pointer

edited May 08 '14 at 12:58

answered May 08 '14 at 09:42

snehal

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Thanks, these tutorials are very helpful. Especially for C++ beginners. – modulitos May 08 '14 at 09:48

What does ** mean in C++?

3 Answers3

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