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digitalmars.D.learn - std.socket + sending of structs

reply "Alexander Panek" <alexander.panek brainsware.org> writes:
Hello,

I`m coding a little library for InSim (programmable interface for Live for  
Speed - an online racing simulator) and I`d have to send data in form of  
structs to the server, but socket.send() does only permit void[]`s as data.

So how do I send structs? Or how can i convert them?

Regards,
Alex

-- 
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
Jun 14 2005
next sibling parent reply "Regan Heath" <regan netwin.co.nz> writes:
On Wed, 15 Jun 2005 01:41:57 +0200, Alexander Panek  
<alexander.panek brainsware.org> wrote:

 Hello,

 I`m coding a little library for InSim (programmable interface for Live  
 for Speed - an online racing simulator) and I`d have to send data in  
 form of structs to the server, but socket.send() does only permit  
 void[]`s as data.

 So how do I send structs? Or how can i convert them?



Convert them:

struct oof {}

void main() {
   TcpSocket s;
   oof foo;
   s.send((cast(void*)&foo)[0..oof.sizeof]);
}

Regan
Jun 14 2005
next sibling parent "Regan Heath" <regan netwin.co.nz> writes:
Of course, you have to consider Endian issues i.e. sending from a Big  
Endian to a Little Endian machine will result in garbage, unless you  
convert the endian-ness of the data.

The other option is to convert the struct into some textual representation  
and transfer it that way, this uses more bandwidth, but is less  
complicated.

Regan

On Wed, 15 Jun 2005 11:54:10 +1200, Regan Heath <regan netwin.co.nz> wrote:

 On Wed, 15 Jun 2005 01:41:57 +0200, Alexander Panek  
 <alexander.panek brainsware.org> wrote:

 Hello,

 I`m coding a little library for InSim (programmable interface for Live  
 for Speed - an online racing simulator) and I`d have to send data in  
 form of structs to the server, but socket.send() does only permit  
 void[]`s as data.

 So how do I send structs? Or how can i convert them?



 Convert them:

 struct oof {}

 void main() {
    TcpSocket s;
    oof foo;
    s.send((cast(void*)&foo)[0..oof.sizeof]);
 }

 Regan
Jun 14 2005
prev sibling next sibling parent reply Derek Parnell <derek psych.ward> writes:
On Wed, 15 Jun 2005 11:54:10 +1200, Regan Heath wrote:


 On Wed, 15 Jun 2005 01:41:57 +0200, Alexander Panek  
 <alexander.panek brainsware.org> wrote:

 Hello,

 I`m coding a little library for InSim (programmable interface for Live  
 for Speed - an online racing simulator) and I`d have to send data in  
 form of structs to the server, but socket.send() does only permit  
 void[]`s as data.

 So how do I send structs? Or how can i convert them?



 Convert them:
 
 struct oof {}
 
 void main() {
    TcpSocket s;
    oof foo;
    s.send((cast(void*)&foo)[0..oof.sizeof]);
 }
 



Ok, that's neat. 

So in the general case, can one 'cast' anything to a dynamic array of 'x'
using the format ...

   (cast(x*)&q)[0..q.sizeof/x.sizeof]

so long as the q.sizeof was an integral multiple of x.sizeof

-- 
Derek
Melbourne, Australia
15/06/2005 10:13:29 AM
Jun 14 2005
parent "Regan Heath" <regan netwin.co.nz> writes:
On Wed, 15 Jun 2005 10:24:45 +1000, Derek Parnell <derek psych.ward> wrote:

 On Wed, 15 Jun 2005 11:54:10 +1200, Regan Heath wrote:


 On Wed, 15 Jun 2005 01:41:57 +0200, Alexander Panek
 <alexander.panek brainsware.org> wrote:

 Hello,

 I`m coding a little library for InSim (programmable interface for Live
 for Speed - an online racing simulator) and I`d have to send data in
 form of structs to the server, but socket.send() does only permit
 void[]`s as data.

 So how do I send structs? Or how can i convert them?



 Convert them:

 struct oof {}

 void main() {
    TcpSocket s;
    oof foo;
    s.send((cast(void*)&foo)[0..oof.sizeof]);
 }



 Ok, that's neat.

 So in the general case, can one 'cast' anything to a dynamic array of 'x'
 using the format ...

    (cast(x*)&q)[0..q.sizeof/x.sizeof]

 so long as the q.sizeof was an integral multiple of x.sizeof



Yeah, I believe so. Though consider/remember:

char[] a = "regan";
(cast(byte*)&a)[0..a.sizeof/byte.sizeof];

That would be incorrect. You'd need:

(cast(byte*)&a.ptr)[0..a.length];

Regan
Jun 14 2005
prev sibling parent reply Chris Sauls <ibisbasenji gmail.com> writes:
Regan Heath wrote:

 struct oof {}
 
 void main() {
   TcpSocket s;
   oof foo;
   s.send((cast(void*)&foo)[0..oof.sizeof]);
 }



Maybe I'm forgetting something -- it's likely -- but couldn't one just cast
directly to a 
void[]?  Aka:

# struct oof {}
#
# void main() {
#   TcpSocket s;
#   oof foo;
#   s.send(cast(void[])oof);
# }

I'm under the impression that type void[] is meant to be D's "I might be
anything" type, 
rather than void*.  Could be wrong.  Haven't tested this.

-- Chris Sauls
Jun 14 2005
parent "Regan Heath" <regan netwin.co.nz> writes:
On Wed, 15 Jun 2005 00:46:05 -0500, Chris Sauls <ibisbasenji gmail.com>  
wrote:

 Regan Heath wrote:

 struct oof {}
  void main() {
   TcpSocket s;
   oof foo;
   s.send((cast(void*)&foo)[0..oof.sizeof]);
 }



 Maybe I'm forgetting something -- it's likely -- but couldn't one just  
 cast directly to a void[]?  Aka:

 # struct oof {}
 #
 # void main() {
 #   TcpSocket s;
 #   oof foo;
 #   s.send(cast(void[])oof);
 # }

 I'm under the impression that type void[] is meant to be D's "I might be  
 anything" type, rather than void*.  Could be wrong.  Haven't tested this.



Sadly, no, these attempts give these errors:

s.send(cast(void[])foo);  //e2ir: cannot cast from oof to void[]
s.send(cast(void[])&foo); //cannot cast oof * to void[]
s.send(cast(void[])&foo[0..foo.sizeof]); //oof cannot be sliced with []

The reason the initial suggestion works is due to the "type X* can be  
sliced to give X[]" rule. The other rule is "X[] is implicitly castable to  
void[]"... If we combine these rules we get:

s.send((&foo)[0..foo.sizeof]);

Which works!

NOTE: The () are required around &foo, as the [] 'slice' operator has  
higher precedence than the & 'address' operator.

Regan
Jun 15 2005
prev sibling parent Derek Parnell <derek psych.ward> writes:
On Wed, 15 Jun 2005 01:41:57 +0200, Alexander Panek wrote:


 Hello,
 
 I`m coding a little library for InSim (programmable interface for Live for  
 Speed - an online racing simulator) and I`d have to send data in form of  
 structs to the server, but socket.send() does only permit void[]`s as data.
 
 So how do I send structs? Or how can i convert them?



This example code might be a starting point ...
<code>
import std.stdio;

struct data
{
  char[4] fldA;
  int     fldB;
  long    fldC;
}

void func(void[] a)
{
    writefln("Size %d", a.length);
    foreach(ubyte b; cast(ubyte[])a)
        writef("%2x", b);
}

void main()
{
   union db
   {
    // Here is where we update flds.
    data d;
    // Overlay the struct with a byte array.
    ubyte[data.sizeof] z;
   }
   db y;

   y.d.fldA[] = "abcd";
   y.d.fldB = 7281242;
   y.d.fldC = 987656676274;
   func( y.z );
}

</code>


-- 
Derek
Melbourne, Australia
15/06/2005 9:48:42 AM
Jun 14 2005