It’s in memory — or in a memory-mapped file. How do I reinterpret at an offset
in an array?
On March 23, 2015 at 5:03:47 PM, Tobias Knopp (tobias.kn...@googlemail.com)
wrote:
Is the data in a file or already read into an array? If it is still in the file
you can simply read the data using the read function. If the data is read as an
Uint8 array you can use an immutable and reinterprete into it. This does
however not work if the C-struct would contain fixed-size array data.
Cheers
Tobi
Am Montag, 23. März 2015 20:20:09 UTC+1 schrieb Sebastian Good:
I'm trying to read some binary formatted data. In C, I would define an
appropriately padded struct and cast away. Is is possible to do something
similar in Julia, though for only one value at a time? Philosophically, I'd
like to approximate the following, for some simple bittypes T (Int32, Float32,
etc.)
T read<T>(char* data, size_t offset) { return *(T*)(data + offset); }
The transliteration of this brain-dead approach results in the following, which
seems to allocate a boxed Pointer object on every invocation. The pointer
function comes with ample warnings about how it shouldn't be used, and I
imagine that it's not polite to the garbage collector.
prim_read{T}(::Type{T},
data::AbstractArray{Uint8,
1},
byte_number)
=
unsafe_load(convert(Ptr{T},
pointer(data,
byte_number)))
I can reinterpret the whole array, but this will involve a division of the
offset to calculate the new offset relative to the reinterpreted array, and it
allocates an array object.
Is there a better way to simply read the machine word at a particular offset in
a byte array? I would think it should inline to a single assembly instruction
if done right.
