CODEWITHSUNDEEP
cpointersincrement
Nicholas Corin
Nicholas Corin

Reputation: 2404

++ Operator on pointers

My CS course is taking a bit of a turn from Java to C. I'm busy going over pointers at the moment and I have come across that the ++ operator for incrementing doens't work when dereferencing. This is more just a curiosity question than anything else. Just not used to the pointers concept just yet. Am I just doing something wrong or is it something to do with pointers?

For example:

*pointer++; Will not increment the value.
*pointer+=1; Will increment the value.

Thanks in advance!

Upvotes: 2

Views: 256

Answers (5)

Jiminion
Jiminion

Reputation: 5168

*pointer++ increments the pointer variable, not value pointed by it.

int array[4] = {3,5,7,9};

int *pointer = array;

// *pointer equals 3

*pointer++;

// *pointer now equals 5

Upvotes: 4

Grijesh Chauhan
Grijesh Chauhan

Reputation: 58291

*pointer++; is almost equivalent to: 

*pointer;
pointer = pointer + 1;

Why its so?

In expression *pointer++;, ++ is postfix operator, so fist * deference operation performed then ++ increments value of pointer (and not increments value).

Whereas *pointer += 1 is just equivalent to: 

*pointer =  *pointer + 1;

that increments value pointed by pointer.

Upvotes: 2

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726987

This has to do with precedence of the operators: post-increment ++ has higher precedence than the dereference operator *, while += has lower precedence in the table of operator precedences. That is why in the first example ++ is applied to the pointer which is dereferenced afterwards, while in the second example += 1 is applied to the result of dereference.

Upvotes: 2

ouah
ouah

Reputation: 145899

*pointer++;

is equivalent to 

*(pointer++);  // pointer is incremented

and not to

 (*pointer)++;  // pointee is incremented

Upvotes: 4

Scotty Bauer
Scotty Bauer

Reputation: 1277

When you want to increment the value you have to make sure you use parenthesis.

(*pointer)++;

Upvotes: 5

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