Re: New warning in Xcode 7
Re: New warning in Xcode 7
- Subject: Re: New warning in Xcode 7
- From: John McCall <email@hidden>
- Date: Tue, 13 Oct 2015 15:56:46 -0700
> On Oct 13, 2015, at 3:24 PM, Graham Cox <email@hidden> wrote:
> In a piece of code I haven’t worked on in a while, I’m suddenly getting a new warning which I’ve never seen before:
>
> “Multiple unsequenced modifications to ‘ix’”
>
> Code is:
>
>
> ix = ++ix % guess.count;
>
> where ix is a NSUInteger.
>
> Is this telling me that the order of the preincrement and the mod operation is undefined? Surely a preincrement is defined to happen first, that’s why it’s called a PREincrement? Or does the warning refer to something else? I’ve used this form of expression for years without any issues, why is it suddenly one?
Pre-increment is defined to return the value that would be stored in its operand. The actual store to the operand is indeterminately sequenced with returning that value, however.
John.
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