• mcl (22/22) Sep 09 2004 I'm stuck. What is the best way to convert a struct to a void[]? I'm u...
• Regan Heath (16/40) Sep 09 2004 It's a little known fact that you can slice a pointer giving you an arra...
• Derek Parnell (11/58) Sep 09 2004 It does! And you don't need a template either.
• Regan Heath (5/60) Sep 09 2004 Yeah. I assumed there was a reason for using a template.
• mcl (5/66) Sep 10 2004 The reason for the template was to abstract the code for use with differ...
• Russ Lewis (3/14) Sep 10 2004 Yes. If you want to copy it, then just append .dup:
• Nick (5/6) Sep 11 2004 By the way, it's (&f)[0..1], not (&f)[0..f.sizeof]. If f is a Foo then (...
• Regan Heath (8/15) Sep 12 2004 Ahhh, yes, but in this case...
• Sean Kelly (3/22) Sep 12 2004 But Nick isn't casting to void so it's a pointer to Foo.
• Regan Heath (7/28) Sep 13 2004 I know.
• Nick (3/10) Sep 13 2004 That is correct.
• Sha Chancellor (4/19) Sep 12 2004 That reeks of nasty hack. Why slice a pointer to cast a struct into a
• Regan Heath (18/39) Sep 12 2004 Not to me, but then I work in C most of the time.
• Sha Chancellor (13/63) Sep 25 2004 I guess this bothers me:
• Ivan Senji (11/73) Sep 26 2004
• Sha Chancellor (3/18) Sep 26 2004 Hmmm.. That make sense now. But, I still don't like how it looks.
• Vathix (5/8) Sep 09 2004 using the
• Regan Heath (6/15) Sep 09 2004 Duh.. (/me smacks my head) of course.
• Helmut Leitner (6/17) Sep 09 2004 Makes a nice FAQ entry:
• Garett Bass (10/12) Sep 12 2004 A word of warning... When sending structured data over the

mcl <mcl_member pathlink.com> writes:

I'm stuck.  What is the best way to convert a struct to a void[]?  I'm using the
socket library in phobos and I want to send an aligned struct over the network.
Here's the best solution I've come up with so far...

#template Yuck(T)













To convert a struct to void[], I use the following...

#struct Foo { ... }

#Foo f;
#void[] fv = Yuck!(Foo).toVoid(f);

Please tell me there is a better way to do this...

Regan Heath <regan netwin.co.nz> writes:

On Fri, 10 Sep 2004 01:44:51 +0000 (UTC), mcl <mcl_member pathlink.com> 
wrote:

 I'm stuck.  What is the best way to convert a struct to a void[]?  I'm 
 using the
 socket library in phobos and I want to send an aligned struct over the 
 network.
 Here's the best solution I've come up with so far...

 #template Yuck(T)













 To convert a struct to void[], I use the following...

 #struct Foo { ... }

 #Foo f;
 #void[] fv = Yuck!(Foo).toVoid(f);

 Please tell me there is a better way to do this...

It's a little known fact that you can slice a pointer giving you an array. 
Slicing a void* will give you a void[]. You can also cast any memory 
address to a void*, So...

template toVoid(Struct)
{
   void[] toVoid(inout Struct s)
   {
     return (cast(void*)&s)[0..s.sizeof];
   }
}

should do it.

Regan

-- 
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Derek Parnell <derek psych.ward> writes:

On Fri, 10 Sep 2004 14:22:56 +1200, Regan Heath wrote:

 On Fri, 10 Sep 2004 01:44:51 +0000 (UTC), mcl <mcl_member pathlink.com> 
 wrote:
 
 I'm stuck.  What is the best way to convert a struct to a void[]?  I'm 
 using the
 socket library in phobos and I want to send an aligned struct over the 
 network.
 Here's the best solution I've come up with so far...

 #template Yuck(T)













 To convert a struct to void[], I use the following...

 #struct Foo { ... }

 #Foo f;
 #void[] fv = Yuck!(Foo).toVoid(f);

 Please tell me there is a better way to do this...

 
 It's a little known fact that you can slice a pointer giving you an array. 
 Slicing a void* will give you a void[]. You can also cast any memory 
 address to a void*, So...
 
 template toVoid(Struct)
 {
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }
 }
 
 should do it.
 
 Regan

It does! And you don't need a template either.

Foo f;
void[] fv = (cast(void*)&f)[0..f.sizeof];

writefln("%d", fv.length);
writefln("%X", cast(uint)&fv[0]);
writefln("%X", cast(uint)&f);

-- 
Derek
Melbourne, Australia
10/Sep/04 12:45:22 PM

Regan Heath <regan netwin.co.nz> writes:

On Fri, 10 Sep 2004 12:49:47 +1000, Derek Parnell <derek psych.ward> wrote:
 On Fri, 10 Sep 2004 14:22:56 +1200, Regan Heath wrote:

 On Fri, 10 Sep 2004 01:44:51 +0000 (UTC), mcl <mcl_member pathlink.com>
 wrote:

 I'm stuck.  What is the best way to convert a struct to a void[]?  I'm
 using the
 socket library in phobos and I want to send an aligned struct over the
 network.
 Here's the best solution I've come up with so far...

 #template Yuck(T)













 To convert a struct to void[], I use the following..

 #struct Foo { ... }

 #Foo f;
 #void[] fv = Yuck!(Foo).toVoid(f);

 Please tell me there is a better way to do this...

 It's a little known fact that you can slice a pointer giving you an 
 array.
 Slicing a void* will give you a void[]. You can also cast any memory
 address to a void*, So...

 template toVoid(Struct)
 {
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }
 }

 should do it.

 Regan

 It does! And you don't need a template either.

 Foo f;
 void[] fv = (cast(void*)&f)[0..f.sizeof];

 writefln("%d", fv.length);
 writefln("%X", cast(uint)&fv[0]);
 writefln("%X", cast(uint)&f);

Yeah. I assumed there was a reason for using a template.

Regan

-- 
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mcl <mcl_member pathlink.com> writes:

In article <opsd3hv4o15a2sq9 digitalmars.com>, Regan Heath says...
On Fri, 10 Sep 2004 12:49:47 +1000, Derek Parnell <derek psych.ward> wrote:
 On Fri, 10 Sep 2004 14:22:56 +1200, Regan Heath wrote:

 On Fri, 10 Sep 2004 01:44:51 +0000 (UTC), mcl <mcl_member pathlink.com>
 wrote:

 I'm stuck.  What is the best way to convert a struct to a void[]?  I'm
 using the
 socket library in phobos and I want to send an aligned struct over the
 network.
 Here's the best solution I've come up with so far...

 #template Yuck(T)













 To convert a struct to void[], I use the following..

 #struct Foo { ... }

 #Foo f;
 #void[] fv = Yuck!(Foo).toVoid(f);

 Please tell me there is a better way to do this...

 It's a little known fact that you can slice a pointer giving you an 
 array.
 Slicing a void* will give you a void[]. You can also cast any memory
 address to a void*, So...

 template toVoid(Struct)
 {
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }
 }

 should do it.

 Regan

 It does! And you don't need a template either.

 Foo f;
 void[] fv = (cast(void*)&f)[0..f.sizeof];

 writefln("%d", fv.length);
 writefln("%X", cast(uint)&fv[0]);
 writefln("%X", cast(uint)&f);

Yeah. I assumed there was a reason for using a template.


The reason for the template was to abstract the code for use with different
structs since it's a bit complicated. The slice trick is far more elegant, since
it's a one-liner.  My only concern: Is the pointer slice in place?   I could see
this being a problem with stack allocated structs/classes...   

Russ Lewis <spamhole-2001-07-16 deming-os.org> writes:

mcl wrote:
Foo f;
void[] fv = (cast(void*)&f)[0..f.sizeof];

writefln("%d", fv.length);
writefln("%X", cast(uint)&fv[0]);
writefln("%X", cast(uint)&f);


 
 The reason for the template was to abstract the code for use with different
 structs since it's a bit complicated. The slice trick is far more elegant,
since
 it's a one-liner.  My only concern: Is the pointer slice in place?   I could
see
 this being a problem with stack allocated structs/classes...   

Yes.  If you want to copy it, then just append .dup:

void[] fv = (&f)[0..f.sizeof].dup;

Nick <Nick_member pathlink.com> writes:

In article <cht6ve$1vma$1 digitaldaemon.com>, Russ Lewis says...
void[] fv = (&f)[0..f.sizeof].dup;

By the way, it's (&f)[0..1], not (&f)[0..f.sizeof]. If f is a Foo then (&f) is
of type (Foo*), so a slice of one element will include one entire struct. I have
corrected this in the wiki as well.

Nick

Regan Heath <regan netwin.co.nz> writes:

On Sat, 11 Sep 2004 12:56:07 +0000 (UTC), Nick <Nick_member pathlink.com> 
wrote:
 In article <cht6ve$1vma$1 digitaldaemon.com>, Russ Lewis says...
 void[] fv = (&f)[0..f.sizeof].dup;

 By the way, it's (&f)[0..1], not (&f)[0..f.sizeof]. If f is a Foo then 
 (&f) is of type (Foo*), so a slice of one element will include one 
 entire struct. I have corrected this in the wiki as well.

Ahhh, yes, but in this case...

(cast(void*)&f)[0..f.sizeof]

it is f.sizeof, isn't it? because void has a size of 1.

Regan

-- 
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Sean Kelly <sean f4.ca> writes:

Regan Heath wrote:

 On Sat, 11 Sep 2004 12:56:07 +0000 (UTC), Nick 
 <Nick_member pathlink.com> wrote:
 
 In article <cht6ve$1vma$1 digitaldaemon.com>, Russ Lewis says...

 void[] fv = (&f)[0..f.sizeof].dup;

 By the way, it's (&f)[0..1], not (&f)[0..f.sizeof]. If f is a Foo then 
 (&f) is of type (Foo*), so a slice of one element will include one 
 entire struct. I have corrected this in the wiki as well.

 
 
 Ahhh, yes, but in this case...
 
 (cast(void*)&f)[0..f.sizeof]
 
 it is f.sizeof, isn't it? because void has a size of 1.

But Nick isn't casting to void so it's a pointer to Foo.


Sean

Regan Heath <regan netwin.co.nz> writes:

On Sun, 12 Sep 2004 22:08:05 -0700, Sean Kelly <sean f4.ca> wrote:
 Regan Heath wrote:

 On Sat, 11 Sep 2004 12:56:07 +0000 (UTC), Nick 
 <Nick_member pathlink.com> wrote:

 In article <cht6ve$1vma$1 digitaldaemon.com>, Russ Lewis says...

 void[] fv = (&f)[0..f.sizeof].dup;

 By the way, it's (&f)[0..1], not (&f)[0..f.sizeof]. If f is a Foo then 
 (&f) is of type (Foo*), so a slice of one element will include one 
 entire struct. I have corrected this in the wiki as well.


 Ahhh, yes, but in this case...

 (cast(void*)&f)[0..f.sizeof]

 it is f.sizeof, isn't it? because void has a size of 1.

 But Nick isn't casting to void so it's a pointer to Foo.

I know.

I was simply pointing out the original suggestion wasn't buggy, it turned 
buggy when someone changed a part of it. :)

Regan

-- 
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Nick <Nick_member pathlink.com> writes:

In article <opsd8ixnk45a2sq9 digitalmars.com>, Regan Heath says...
 Nick:
 By the way, it's (&f)[0..1], not (&f)[0..f.sizeof]. If f is a Foo then 
 (&f) is of type (Foo*), so a slice of one element will include one 
 entire struct. I have corrected this in the wiki as well.

Ahhh, yes, but in this case...

(cast(void*)&f)[0..f.sizeof]

it is f.sizeof, isn't it? because void has a size of 1.

That is correct.

Nick

Sha Chancellor <schancel pacific.net> writes:

In article <opsd298iol5a2sq9 digitalmars.com>,
 Regan Heath <regan netwin.co.nz> wrote:

 It's a little known fact that you can slice a pointer giving you an array. 
 Slicing a void* will give you a void[]. You can also cast any memory 
 address to a void*, So...
 
 template toVoid(Struct)
 {
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }
 }
 
 should do it.
 
 Regan

That reeks of nasty hack.   Why slice a pointer to cast a struct into a 
void[] ???  Why can't it just be cast directly?

Regan Heath <regan netwin.co.nz> writes:

On Sun, 12 Sep 2004 07:23:08 -0700, Sha Chancellor <schancel pacific.net> 
wrote:
 In article <opsd298iol5a2sq9 digitalmars.com>,
  Regan Heath <regan netwin.co.nz> wrote:

 It's a little known fact that you can slice a pointer giving you an 
 array.
 Slicing a void* will give you a void[]. You can also cast any memory
 address to a void*, So...

 template toVoid(Struct)
 {
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }
 }

 should do it.

 Regan

 That reeks of nasty hack.

Not to me, but then I work in C most of the time.

 Why slice a pointer to cast a struct into a
 void[] ???  Why can't it just be cast directly?

Good question, it probably could with some compiler magic, after all a 
void[] is simply a pointer and a length, the compiler knows the length of 
the object..

Arrays already implicitly cast to void[] eg.

void foo(void[] p)
{
}

void main()
{
   char[] string = "regan";
   foo(string);
}

Regan

-- 
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Sha Chancellor <schancel pacific.net> writes:

In article <opsd8ly80b5a2sq9 digitalmars.com>,
 Regan Heath <regan netwin.co.nz> wrote:

 On Sun, 12 Sep 2004 07:23:08 -0700, Sha Chancellor <schancel pacific.net> 
 wrote:
 In article <opsd298iol5a2sq9 digitalmars.com>,
  Regan Heath <regan netwin.co.nz> wrote:

 It's a little known fact that you can slice a pointer giving you an 
 array.
 Slicing a void* will give you a void[]. You can also cast any memory
 address to a void*, So...

 template toVoid(Struct)
 {
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }
 }

 should do it.

 Regan

 That reeks of nasty hack.

 
 Not to me, but then I work in C most of the time.
 
 Why slice a pointer to cast a struct into a
 void[] ???  Why can't it just be cast directly?

 
 Good question, it probably could with some compiler magic, after all a 
 void[] is simply a pointer and a length, the compiler knows the length of 
 the object..
 
 Arrays already implicitly cast to void[] eg.
 
 void foo(void[] p)
 {
 }
 
 void main()
 {
    char[] string = "regan";
    foo(string);
 }
 
 Regan

I guess this bothers me:
 
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }



You cast a pointer of S to a void* and then do an array slice.   If you 
can slice it like an array, why do you need to slice it at all? Why 
can't it be implicit cast to void[] from a void* in the first place?  
Why is slicing necessary?

IE:

return (cast(void[])&s);
or return (cast(void*)&s); 

Will either of those work?

I don't have a D compiler handy.

"Ivan Senji" <ivan.senji public.srce.hr> writes:

"Sha Chancellor" <schancel pacific.net> wrote in message
news:schancel-0064DE.14485525092004 digitalmars.com...
 In article <opsd8ly80b5a2sq9 digitalmars.com>,
  Regan Heath <regan netwin.co.nz> wrote:

 On Sun, 12 Sep 2004 07:23:08 -0700, Sha Chancellor


<schancel pacific.net>
 wrote:
 In article <opsd298iol5a2sq9 digitalmars.com>,
  Regan Heath <regan netwin.co.nz> wrote:

 It's a little known fact that you can slice a pointer giving you an
 array.
 Slicing a void* will give you a void[]. You can also cast any memory
 address to a void*, So...

 template toVoid(Struct)
 {
    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }
 }

 should do it.

 Regan

 That reeks of nasty hack.

 Not to me, but then I work in C most of the time.

 Why slice a pointer to cast a struct into a
 void[] ???  Why can't it just be cast directly?

 Good question, it probably could with some compiler magic, after all a
 void[] is simply a pointer and a length, the compiler knows the length


of
 the object..

 Arrays already implicitly cast to void[] eg.

 void foo(void[] p)
 {
 }

 void main()
 {
    char[] string = "regan";
    foo(string);
 }

 Regan

 I guess this bothers me:

    void[] toVoid(inout Struct s)
    {
      return (cast(void*)&s)[0..s.sizeof];
    }



 You cast a pointer of S to a void* and then do an array slice.   If you
 can slice it like an array, why do you need to slice it at all? Why
 can't it be implicit cast to void[] from a void* in the first place?
 Why is slicing necessary?

Because void[] has a length property and a void* doesn't,
if we could implicitly cast void* to void[] what length would that
array have? That is what slicing is there for, to give array length,
it is also a documented way of making bounds checked array out of
a pointer.

 IE:

 return (cast(void[])&s);
 or return (cast(void*)&s);

 Will either of those work?

No, first is Struct* to void[]
the second is void* to return type void[]

 I don't have a D compiler handy.

Sha Chancellor <schancel pacific.net> writes:

In article <cj5qg7$2uod$1 digitaldaemon.com>,
 "Ivan Senji" <ivan.senji public.srce.hr> wrote:

 Because void[] has a length property and a void* doesn't,
 if we could implicitly cast void* to void[] what length would that
 array have? That is what slicing is there for, to give array length,
 it is also a documented way of making bounds checked array out of
 a pointer.
 
 IE:

 return (cast(void[])&s);
 or return (cast(void*)&s);

 Will either of those work?

 
 No, first is Struct* to void[]
 the second is void* to return type void[]

Hmmm..  That make sense now. But, I still don't like how it looks.

"Vathix" <vathixSpamFix dprogramming.com> writes:

"mcl" <mcl_member pathlink.com> wrote in message
news:chr0uj$rvk$1 digitaldaemon.com...
 I'm stuck.  What is the best way to convert a struct to a void[]?  I'm

using the
 socket library in phobos and I want to send an aligned struct over the

network.
 Here's the best solution I've come up with so far...

(&f)[0 .. 1]  works just fine. Any array implicitly converts to void[].

Regan Heath <regan netwin.co.nz> writes:

On Fri, 10 Sep 2004 01:15:15 -0400, Vathix 
<vathixSpamFix dprogramming.com> wrote:
 "mcl" <mcl_member pathlink.com> wrote in message
 news:chr0uj$rvk$1 digitaldaemon.com...
 I'm stuck.  What is the best way to convert a struct to a void[]?  I'm

 using the
 socket library in phobos and I want to send an aligned struct over the

 network.
 Here's the best solution I've come up with so far...

 (&f)[0 .. 1]  works just fine. Any array implicitly converts to void[].

Duh.. (/me smacks my head) of course.

Regan

-- 
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Helmut Leitner <leitner hls.via.at> writes:

Vathix wrote:
 
 "mcl" <mcl_member pathlink.com> wrote in message
 news:chr0uj$rvk$1 digitaldaemon.com...
 I'm stuck.  What is the best way to convert a struct to a void[]?  I'm

 using the
 socket library in phobos and I want to send an aligned struct over the

 network.
 Here's the best solution I've come up with so far...

 
 (&f)[0 .. 1]  works just fine. Any array implicitly converts to void[].

Makes a nice FAQ entry:
   <http://www.wikiservice.at/wiki4d/wiki.cgi?FaqRoadmap#Howtoconverttovoid>

-- 
Helmut Leitner    leitner hls.via.at
Graz, Austria   www.hls-software.com

"Garett Bass" <gtbass studiotekne.com> writes:

"mcl" wrote:
 I'm using the socket library in phobos and I
 want to send an aligned struct over the network.

A word of warning... When sending structured data over the 
network, keep in mind the endianness of the client and 
server may (eventually) be different.  For example, *if* 
there were a D compiler for non-x86-based platforms, such as 
the Mac, your struct could be sent from a Big-endian machine 
to a little-endian machine.  This would FUBAR any 
float/double (and multibyte integer, I think) data you may 
have in your struct, since machines of different endianness 
interpret multibyte datatypes differently.