Problems assigning incremented values to CGPointMake

Question

I'm trying to use the following code to move through pages of a Pdf using webView.

 float Y = pdfNavigateController.webView.center.y + gY;
 [pdfNavigateController.webView.scrollView setContentOffset:CGPointMake(0,Y)];

The value gY is also a float and is incremented as the user selects the next page. The code is currently throwing an error 'Invalid operands to binary expression ('CGFloat' (aka 'float') and 'float *'). I'm guessing the operands are invalid as the value is a pointer but I don't know how to pass the incremented value without getting this error.

Answer 1

If gY is a pointer (to a float), you need to dereference it in order to access its value:

float Y = pdfNavigateController.webView.center.y + *gY;

EDIT

Make sure you've got a valid pointer (i.e., gY points to an actual float). If it's an un-initialized pointer, it won't work.

Can you please tell us how do you get gY?

EDIT 2

I've seen you said that gY is declared as:

static float *gY = 0;

That's a NULL pointer.
And you can't dereference a NULL pointer.

When you increment it, you increment the pointer (the memory address), not the value. So your pointer actually points to garbage.

Why do you use a pointer? You should use:

static float gY = 0;

Answer 2

if gY is a pointer to a float use *gY:

float Y = pdfNavigateController.webView.center.y + *gY;

The error rmessage: ('CGFloat' (aka 'float') and 'float *') is saying that CGFloat expected a float but got a float pointer: float *

For debugging first break the operation down into accessing the value pointed to.

float gYValue = *gY;
float Y = pdfNavigateController.webView.center.y + gYValue;

Answer 3

It is hard to troubleshoot since you've posted very small amount of your code. However I have an idea. If the gX is an argument of a method the solution may be following:

In order to fix this problem, add the declaration of the method to the .h file for your class. Hope this will help - if not please post some more code.