increment value of int being pointed to by pointer

Question

I have an int pointer (int *count) if i want to increment the integer being pointed at using ++ I thought I would call

*count++;

However, I am getting a build warning "expression result unused". I can call

*count += 1;

But, I would like to know how to use the ++. Any ideas?

Answer 1

Try using (*count)++. *count++ might be incrementing the pointer to next position and then using indirection (which is unintentional).

Answer 2

The ++ has equal precedence with the * and the associativity is right-to-left. See here. It's made even more complex because even though the ++ will be associated with the pointer the increment is applied after the statement's evaluation.

The order things happen is:

1. Post increment, remember the post-incremented pointer address value as a temporary
2. Dereference non-incremented pointer address
3. Apply the incremented pointer address to count, count now points to the next possible memory address for an entity of its type.

You get the warning because you never actually use the dereferenced value at step 2. Like @Sidarth says, you'll need parenthesis to force the order of evaluation:

 (*ptr)++