"ptr = ptr - > next" What does this "->" mean? (C++)

Question

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What can I use instead of the arrow operator, ->?
What does -> mean in C++?

So I'm currently studying for a C++ exam about Data Structure and Algorithm Development. While looking though my teacher powerpoints, I've noticed that he's used this "->" a lot. And I'm not sure what it means? Is it really a command you can do in c++?

Example 1

addrInfo *ptr = head;
while (ptr->next != NULL) 
{
        ptr = ptr->next;
}   
// at this point, ptr points to the last item

Example 2

if( head == NULL )
{
head = block;
block->next = NULL;
}

Just an additional comment, the `->` operator is called the 'pointer to member' operator. I'm not sure why so many people don't have a name for it. — Collin Dauphinee, Mar 07 '12 at 03:38

score 8 · Accepted Answer · answered Mar 07 '12 at 03:25

8

It is a combination dereference and member-access. This ptr->next is equivalent to (*ptr).next.

answered Mar 07 '12 at 03:25

Gordon Bailey

3,803
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28

score 5 · Answer 2 · answered Mar 07 '12 at 03:27

The -> operator deferences a pointer and retrieves from it the memory index beyond that point indicated by the following name. Thus:

struct foo {
   int bar;
   int baz;
};

struct foo something;
struct foo *ptr = &something;

ptr->bar = 5;
ptr->baz = 10;

In the above, the ptr value will be the memory location of the something structure (that's what the & does: finds the memory location of something). Then the ptr variable is later "dereferenced" by the -> operator so that the ptr->bar memory location (an int) is set to 5 and ptr->baz is set to 10.

score 1 · Answer 3 · answered Mar 07 '12 at 03:26

1

It's de-referencing the pointer. It means "Give me the value of the thing pointed at the address stored at ptr". In this example, ptr is pointing to a list item so ptr->next returns the value of the object's next property.

answered Mar 07 '12 at 03:26

D Stanley

144,385
11
166
231

score 1 · Answer 4 · answered Mar 07 '12 at 03:28

The -> operator is specifically a structure dereference. In block->next it is calling the member variable next of the object which the pointer block points to. See this page for a list of member and pointer operators in C++.

Basically, it's doing the same thing as block.next, were block an object rather than a pointer.

score 1 · Answer 5 · answered Mar 07 '12 at 03:33

-> is an operator of pointer. It is used for pointer to access member.

If you take a look at the defination of "addrInfo", you can find the member "next".

Otherwise, you can see the following example:

struct student
{
int num;
}
struct student stu;
struct student *p;
p=&stu;

These three operations are equal: 1. stu.num 2. (*P).num 3. p->num

"ptr = ptr - > next" What does this "->" mean? (C++)

5 Answers5