ios – EXC_BAD_ACCESS when nslog this magic string

I stumbled throughout that once I used NSLOG to print a string of URLs, I obtained an EXC_BAD_ACCESS crash. Then I do know that if the string accommodates a p.c signal %, I want to put in writing

NSLog(%@, urlStr)

to keep away from it truns into one thing bizarre. However I’m actually curious why such a string will trigger such an impact . So I eliminated all characters that did not trigger a crash, by this far I used to be left with this string“

NSLog("%3Apercent2Fpercent2Fpercent2Fpercent2Fpercent2Fpercent3Fpercent3Dpercent2kpercent3Dpercent2spercent3D")

So the query is: Why nslog this string will trigger a crush, what occurred? I decoded this string and the result’s

://///?=%2k=%2s=

that does’t clarify in any respect.
What I used is Swift by the way in which, does it issues?