I don't know why but when using a template union with a static ubyte array i get bizarre results!

module main;

import std.stdio;
private union ByteConverter(T)
{
	ubyte[T.sizeof] bytes;
	T value;
}

ubyte[] toBytes(T)(T from) if (!is(T == const))
{
	ByteConverter!T converter;
	converter.value = from;
	return converter.bytes;
}

T fromBytes(T)(in ubyte[] bytes)
{
	ByteConverter!T converter;
	converter.bytes = bytes;
	return converter.value;
}

void main(string[] args)
{
	writeln(fromBytes!uint(toBytes(34u)));// should print 32 but prints 1244564
}

why dose it print 1244564 the array is static size so why is it acting like bytes is a pointer not a static array?

On Friday, 29 May 2015 at 07:55:55 UTC, seen wrote:
> I don't know why but when using a template union with a static ubyte array i get bizarre results!
>
> module main;
>
> import std.stdio;
> private union ByteConverter(T)
> {
> 	ubyte[T.sizeof] bytes;
> 	T value;
> }
>
> ubyte[] toBytes(T)(T from) if (!is(T == const))
> {
> 	ByteConverter!T converter;
> 	converter.value = from;
> 	return converter.bytes;
> }
>
> T fromBytes(T)(in ubyte[] bytes)
> {
> 	ByteConverter!T converter;
> 	converter.bytes = bytes;
> 	return converter.value;
> }
>
> void main(string[] args)
> {
> 	writeln(fromBytes!uint(toBytes(34u)));// should print 32 but prints 1244564
> }
>
> why dose it print 1244564 the array is static size so why is it acting like bytes is a pointer not a static array?

http://fr.wikipedia.org/wiki/Endianness#Little_endian

On Friday, 29 May 2015 at 08:00:54 UTC, deadalnix wrote:
> On Friday, 29 May 2015 at 07:55:55 UTC, seen wrote:
>> I don't know why but when using a template union with a static ubyte array i get bizarre results!
>>
>> module main;
>>
>> import std.stdio;
>> private union ByteConverter(T)
>> {
>> 	ubyte[T.sizeof] bytes;
>> 	T value;
>> }
>>
>> ubyte[] toBytes(T)(T from) if (!is(T == const))
>> {
>> 	ByteConverter!T converter;
>> 	converter.value = from;
>> 	return converter.bytes;
>> }
>>
>> T fromBytes(T)(in ubyte[] bytes)
>> {
>> 	ByteConverter!T converter;
>> 	converter.bytes = bytes;
>> 	return converter.value;
>> }
>>
>> void main(string[] args)
>> {
>> 	writeln(fromBytes!uint(toBytes(34u)));// should print 32 but prints 1244564
>> }
>>
>> why dose it print 1244564 the array is static size so why is it acting like bytes is a pointer not a static array?
>
> http://fr.wikipedia.org/wiki/Endianness#Little_endian

endianness should not be an issue since I'm not changing machines
and using static array unions is a common way to convert to bytes in D.

On 05/29/2015 12:55 AM, seen wrote:
> I don't know why but when using a template union with a static ubyte
> array i get bizarre results!
>
> module main;
>
> import std.stdio;
> private union ByteConverter(T)
> {
>      ubyte[T.sizeof] bytes;

That's a fixed-length array (aka static array), which has value semantics.

>      T value;
> }
>
> ubyte[] toBytes(T)(T from) if (!is(T == const))

That function returns a slice to a...

> {
>      ByteConverter!T converter;
>      converter.value = from;
>      return converter.bytes;

... local static array. :(

Replace the return type with

a) auto

b) ubyte[T.sizeof]

> }
>
> T fromBytes(T)(in ubyte[] bytes)
> {
>      ByteConverter!T converter;
>      converter.bytes = bytes;
>      return converter.value;
> }
>
> void main(string[] args)
> {
>      writeln(fromBytes!uint(toBytes(34u)));// should print 32 but prints
> 1244564
> }
>
> why dose it print 1244564 the array is static size so why is it acting
> like bytes is a pointer not a static array?

Now it prints 34. :)

Ali

On Friday, 29 May 2015 at 07:55:55 UTC, seen wrote:
> ubyte[] toBytes(T)(T from) if (!is(T == const))
> {
> 	ByteConverter!T converter;
> 	converter.value = from;
> 	return converter.bytes;
> }

This function is incorrect: it is returning a slice (dynamic array) of a static array, which is located on the stack. The fact that it compiles without error is bug 9279 (https://issues.dlang.org/show_bug.cgi?id=9279).