I have a byte[] A that contains an AJP13 packet, presumably including UTF8 strings.  I need to extract such strings and to place strings in such a buffer.  I'm using:

string s = A[n .. m].dup;  // n and m from prefixed string length/position return s;

to get strings, and

byte[] ba = cast(byte[]) s;
A[n .. n+ba.length] = ba[0 .. $].dup;

to put them.  Are these a) sensible, b) optimal?

Steve Teale wrote:
> I have a byte[] A that contains an AJP13 packet, presumably including UTF8 strings.  I need to extract such strings and to place strings in such a buffer.  I'm using:
> 
> string s = A[n .. m].dup;  // n and m from prefixed string length/position
> return s;
> 
> to get strings, and

That should work, and be optimal unless you can be sure the A array doesn't change while you still need the string (in which case the .dup is unnecessary).

> byte[] ba = cast(byte[]) s;
> A[n .. n+ba.length] = ba[0 .. $].dup;
> 
> to put them.  Are these a) sensible, b) optimal?

This one should work as well, but isn't optimal; the .dup is unnecessary. This should be equivalent but more efficient:
---
A[n .. n+s.length] = cast(byte[]) s;
---

Frits van Bommel Wrote:

> Steve Teale wrote:
> > I have a byte[] A that contains an AJP13 packet, presumably including UTF8 strings.  I need to extract such strings and to place strings in such a buffer.  I'm using:
> > 

> > string s = A[n .. m].dup;  // n and m from prefixed string length/position return s;
> > 
> > to get strings, and
> 
> That should work, and be optimal unless you can be sure the A array doesn't change while you still need the string (in which case the .dup is unnecessary).
> 
> > byte[] ba = cast(byte[]) s;
> > A[n .. n+ba.length] = ba[0 .. $].dup;
> > 
> > to put them.  Are these a) sensible, b) optimal?
> 
> This one should work as well, but isn't optimal; the .dup is unnecessary. This should be equivalent but more efficient:
> ---
> A[n .. n+s.length] = cast(byte[]) s;
> ---

Can I use n+s.length?  In my experimentation i noticed that a UTF8 string containing a character using a two-byte representation definitely had an s.length of the number of characters, which was one less than the number of bytes.

Steve Teale wrote:
> Frits van Bommel Wrote:
> 
>> ---
>> A[n .. n+s.length] = cast(byte[]) s;
>> ---
> 
> Can I use n+s.length?  In my experimentation i noticed that a UTF8 string containing a character using a two-byte representation definitely had an s.length of the number of characters, which was one less than the number of bytes.

You noticed wrong...
char[]s in D aren't very special, they're just specific array types that happen to be handled specially by some functions (such as writef*)[1]. The .length is the number of elements, and each element is a fixed size. A char is just a type representing a byte from UTF-8 text.
---
import std.stdio;

void main() {
	auto s = "\u0100";
	writefln(s);
	writefln(s.length);
	writefln((cast(byte[])s).length);
}
---
Outputs a weird character (an A with a - on top) and two times the number 2.


[1]: and by foreach statements as well; they can automagically extract char/wchar/dchar elements from char[]/wchar[]dchar[], in any combination.

Frits van Bommel Wrote:

> Steve Teale wrote:
> > Frits van Bommel Wrote:
> > 
> >> ---
> >> A[n .. n+s.length] = cast(byte[]) s;
> >> ---
> > 
> > Can I use n+s.length?  In my experimentation i noticed that a UTF8 string containing a character using a two-byte representation definitely had an s.length of the number of characters, which was one less than the number of bytes.
> 
> You noticed wrong...
> char[]s in D aren't very special, they're just specific array types that
> happen to be handled specially by some functions (such as writef*)[1].
> The .length is the number of elements, and each element is a fixed size.
> A char is just a type representing a byte from UTF-8 text.
> ---
> import std.stdio;
> 
> void main() {
> 	auto s = "\u0100";
> 	writefln(s);
> 	writefln(s.length);
> 	writefln((cast(byte[])s).length);
> }
> ---
> Outputs a weird character (an A with a - on top) and two times the number 2.
> 
> 
> [1]: and by foreach statements as well; they can automagically extract char/wchar/dchar elements from char[]/wchar[]dchar[], in any combination.

You are correct, I had misinterpreted my own test program.

Frits van Bommel wrote:
> Outputs a weird character (an A with a - on top) [...]

Hah, Null-A! Reading A.E. van Vogt?

Regards, Frank

0ffh wrote:
> Frits van Bommel wrote:
>> Outputs a weird character (an A with a - on top) [...]
> 
> Hah, Null-A! Reading A.E. van Vogt?

No, never heard of him. I just picked \u0100 because it was a round character code and it happened to be that character...