What is the 'garbage value' in 'Left operand of '/' is a garbage value' warning generated by "Build & Analyze"?
When I 'Build and Analyze" this code in Xcode, I get a warning that I don't understand. Here's the method with the problem:
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch * touch = [touches anyObject];
CGPoint location = [touch locationInView:self];
CGPoint relativePosition = CGPointMake(1.0-(location.x / self.bounds.size.width),location.y / self.bounds.size.height);
[[Stage getSharedStage] movePa开发者_如何学GortToLocation:relativePosition];
}
Here's the warning:
warning: The left operand of '/' is a garbage value
CGPoint relativePosition = CGPointMake(1.0-(location.x / self.bounds.size.width),location.y / self.bounds.size.height);
~~~~~~~~~~ ^
1 warning generated.
Here are the arrows:
What is it trying to tell me? The code works fine.
It's hard to tell without seeing the entire function, but I would take that to mean that there exists a path the code could take where location.x is never initialized. It may be that the code never takes that path in your testing, but the possibility is there.
EDIT: I'm going to take a wild guess here and say that it's because [touches anyObject] could conceivably return nil
. In which case [touch locationInView:self]
will return garbage (remember sending messages to nil
is perfectly valid).
Try making the rest of the function conditional on (touch != nil)
.
If touch is nil, [touch locationInView:] will return the nil struct result, which before some version of llvm would only guarantee that the first [size of pointer] bytes of the struct are zeroed, and the rest would still be garbage.
AFAIK [touches anyObject] can never be nil and the warning is a false positive.
the left operand of '/' is a garbage value ,This suggests tell us that must give an initial value to location.x , because [touch locationInView:self] maybe nil,so Must make a judgment whether the if(touch!=nil)
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