Modifying too many bytes of Data object crashes swift app

Question

I am creating an app where I need to modify specific bytes in a Data object, but it crashes when I modify too many bytes at one time.

I thought the problem might be because my app was hanging for too long, but I put my code in a DispatchGroup and it didn’t help.

//amount and interval are Ints
var pos: Int = 1
let count = data.count
var tempData: Data = data
while (pos < count) {

    tempData[pos - 1] = tempData[pos - 1] + UInt8(amount)

    pos += interval
}

This code crashes my app when I provide it with a large Data object, but works fine with small ones.

I can’t view the exception in any more detail because I am using theos instead of xCode — Bytopo, Aug 14 '19 at 18:02

score 0 · Answer 1 · answered Aug 14 '19 at 19:32

0

I found my problem. Since I was adding two UInt8s together, there was a chance that the resulting UInt8 would be invalid (greater than 255), which resulted in a crash. I fixed this by changing my + to &+ so the UInt8 overflows back to 1.

answered Aug 14 '19 at 19:32

Bytopo

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Modifying too many bytes of Data object crashes swift app

1 Answers1