newbie question about variables in slices..

[Jonathan M Davis via Digitalmars-d-learn]

On Mon, 12 May 2014 20:12:41 +0000
Kai via Digitalmars-d-learn <digitalmars-d-learn at puremagic.com> wrote:

> Hi I am trying to iterate over a mmfile (ubyte[]) and convert it
> to uint
>
> void main(){
>   MmFile inn = new MmFile("mmData.dat");
>   ubyte[] arr = cast(ubyte[])inn[];
>   for(ulong index = 0; index<arr.length; index+=4){
>       ulong stop = index+4;
>       uint num  =
> littleEndianToNative!uint(arr[index..stop]); }
> if i try to compile this i get the following error:
> Error: template std.bitmanip.littleEndianToNative cannot deduce
> function from argument types !(uint)(ubyte[])
>
> but if change the last line to:
> uint num  = littleEndianToNative!uint(arr[30..34]);
>
> then it compiles and runs...
>
> Am I doing something wrong with my variables "index" and "stop"?
> cheers

The problem is that the compiler isn't smart enough to realize that
arr[index .. stop] is guaranteed to result in a array with a length of 4.

auto num = littleEndianToNative!uint(cast(ubyte[4])arr[index..stop]);

would work. On a side note, if you wanted to be safer, you should probably use
uint.sizeof everyewhere instead of 4. that would also make it easier to
convert it to a different integral type. Also, you should be using size_t, not
ulong for the indices. Array indices are size_t, and while that's ulong on a
64-bit system, it's uint on a 32-bit system, so your code won't compile on a
32-bit system.

- Jonathan M Davis