[cfe-dev] Question about arrays in blocks

[jahanian]

On Jun 19, 2013, at 11:45 PM, "Adler, Arik" <arik.adler at intel.com> wrote:

>  
> Another alternative is to copy the pointer and not the whole array (as it done in C)

But this is not the same as capturing the array.
You can get the effect you mentioned by declaring it as __block. Or you can capture the array by putting it in a struct and
capturing the struct instead.

- Fariborz

>  
>  
> From: Eli Friedman [mailto:eli.friedman at gmail.com] 
> Sent: Wednesday, June 19, 2013 20:46
> To: Adler, Arik
> Cc: cfe-dev at cs.uiuc.edu
> Subject: Re: [cfe-dev] Question about arrays in blocks
>  
> On Wed, Jun 19, 2013 at 2:53 AM, Adler, Arik <arik.adler at intel.com> wrote:
>  
> I am now testing blocks usage in OpenCL.
> I noticed that Clang forbids using an arrays within blocks (Clang forbid array capturing)
>  
> For Example, the following code will fail to compile because there is a reference to an array within a block.
> But if the line referring to block will comment out and the line with reference to integer pointer ('j') will comment in, the code will pass.
>  
> void block_arr()
> {
>   int res = 0;
>   int i[4] = { 3, 4, 4, 1 };
>   int* j = i;
>  
>   int (^test_block )(int) = ^(int num)
>     {
>       return num + i[1];      // This is an error: "error: cannot refer to declaration with an array type inside block"
> //      return num + j[1];    // This would work
>     };
>  
>     res = test_block(7);
> }
>  
>  
> Do you know what is the reason behind this limitation?
> And why it is possible to use a regular pointers but arrays are forbidden?
>  
>  
> IIRC, it's just so that people don't accidentally make implicit copies of large arrays.
>  
> -Eli 
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