1. Winsock.ew as a team project...
Hi Euphorians:
Since the coding of Winsock.ew is getting harder,and there are a lot of
functions to implement, any help is very welcome. Greg Harris has joined the
(now) team. For anyone else wishing to collaborate, please send mail.
Currently I'm stuck with a structure accessing problem in the function
gethostbyaddr().
This function returns a pointer to a structure defining host information. In
C/C++ the structure is as follows:
struct hostent{
char FAR * h_name;
char FAR * FAR * h_aliases;
short h_addrtype;
short h_length;
char FAR * FAR * h_addr_list;
};
Since I'm not good at all in C, I do not really understand how to code the
access to this data in Euphoria....
(What does those FAR * FAR * mean?... Pointers to Pointers?... Two
pointers?... Array of pointers?...)
(Help welcome. Join the winsock revolution!)
Homepage: http://www.geocities.com/SiliconValley/Sector/6432/ under
construction.
2. Re: Winsock.ew as a team project...
Jesus Consuegra writes:
> Currently I'm stuck with a structure accessing problem in the
> function gethostbyaddr().
> This function returns a pointer to a structure defining
> host information. In C/C++ the structure is as follows:
> struct hostent{
> char FAR * h_name;
> char FAR * FAR * h_aliases;
> short h_addrtype;
> short h_length;
> char FAR * FAR * h_addr_list;
> };
> Since I'm not good at all in C, I do not really understand
> how to code the access to this data in Euphoria....
> (What does those FAR * FAR * mean?...
> Pointers to Pointers?... Two pointers?... Array of pointers?...)
1. Ignore the word "FAR". Just delete it (in your mind).
It was necessary back in the bad old days of 16-bit
programming where Intel had two types of pointers:
near pointers (16-bit offset), and far pointers (segment plus
offset).
2.
char *h_name;
declares h_name as a pointer to a character (very likely
a pointer to the first character in a string of characters. A
C string is supposed to be terminated by a 0 character.)
char **aliases;
This declares aliases as: a pointer to (a pointer to a character).
So, there is likely an array of pointers to strings somewhere
in memory and aliases points to the first pointer in the array,
call it p0:
aliases --> p0 --> [char 0][char 1][char 2] ... [0]
p1 -->
p2 -->
This "pointer to pointer to pointer ..." stuff is one of the
nastiest things to grasp about C. In Euphoria you would
simply have a sequence of strings:
aliases = {
"fred",
"george",
...
}
3. Things declared as "short" take 2-bytes. char is 1 byte
and int is 4-bytes. (This is not totally standardized in the
C world, but is safe to assume here.)
Regards,
Rob Craig
Rapid Deployment Software
http://members.aol.com/FilesEu/
3. Re: Winsock.ew as a team project...
- Posted by Jacques Deschenes <desja at GLOBETROTTER.QC.CA>
Jul 07, 1998
-
Last edited Jul 08, 1998
At 06:27 07-07-98 +0300, you wrote:
>Hi Euphorians:
>
>Since the coding of Winsock.ew is getting harder,and there are a lot of
>functions to implement, any help is very welcome. Greg Harris has joined the
>(now) team. For anyone else wishing to collaborate, please send mail.
>
>Currently I'm stuck with a structure accessing problem in the function
>gethostbyaddr().
>This function returns a pointer to a structure defining host information. In
>C/C++ the structure is as follows:
>
>struct hostent{
> char FAR * h_name;
> char FAR * FAR * h_aliases;
> short h_addrtype;
> short h_length;
> char FAR * FAR * h_addr_list;
>};
>
>Since I'm not good at all in C, I do not really understand how to code the
>access to this data in Euphoria....
>(What does those FAR * FAR * mean?... Pointers to Pointers?... Two
>pointers?... Array of pointers?...)
>(Help welcome. Join the winsock revolution!)
A FAR pointer in protected mode is 48 bits has it include the selector (16 bits)
and the offset( 32 bits) and a FAR* FAR* is a pointer to a pointer.
So you should allocate 3 * 48 + 2 * 16 bytes for this structure.
constant --offset to access data in the structure.
h_name = 0, -- FAR * is 6 bytes long
h_aliases = 6, -- FAR *
h_addrtype = 12, -- short is 2 bytes
h_length = 14, -- short
h_addr_list = 16 -- FAR *
I didn't test it, hoping I'm right,
Regards,
Jacques Deschenes
Baie-Comeau, Quebec
Canada
desja at globetrotter.qc.ca
4. Re: Winsock.ew as a team project...
Jacques Deschenes writes:
> A FAR pointer in protected mode is 48 bits has it include the
> selector (16 bits) and the offset( 32 bits) and a FAR* FAR*
> is a pointer to a pointer.
> So you should allocate 3 * 48 + 2 * 16 bytes for this structure.
> constant --offset to access data in the structure.
> h_name = 0, -- FAR * is 6 bytes long
> h_aliases = 6, -- FAR *
> h_addrtype = 12, -- short is 2 bytes
> h_length = 14, -- short
> h_addr_list = 16 -- FAR *
>I didn't test it, hoping I'm right,
According to the WIN32 API help file...
"The Application Program Interface (API) for Win32 uses the flat
32-bit addressing mode...One of the major design goals of the
32-bit API was to minimize the impact on existing code, so that
16-bit applications can be adapted as easily as possible. However,
some changes were mandated by the larger address space.
Pointers are all 32 bits wide and no longer near or far, and your
code cannot make assumptions based on segmented memory.
Items which have increased to 32 bits include the following:
· Pointers
· Window handles
· Handles to other objects, such as pens, brushes, and menus
· Graphics coordinates"
Jacques, you are correct that a "far" pointer on the 386 and higher
machines is a 16-bit segment and a 32-bit offset. However in the
flat memory model all pointers use the same segment and
so all C pointers in an application are 32-bits (4 bytes).
The segment number is rarely used for any purpose. (It's used
to set hardware interrupts I suppose.)
I checked the structure (above) that Jesus asked about
using WATCOM C, compiling for 32-bit Windows.
The total size (sizeof) of the structure is 16 bytes.
The constant offsets should be:
h_name = 0, -- pointer is 4 bytes long
h_aliases = 4, -- pointer is 4 bytes long
h_addrtype = 8, -- short is 2 bytes
h_length = 10, -- short is 2 bytes
h_addr_list = 12 -- pointer is 4 bytes long
The FAR keyword is usually #defined in some C .h file
as null string. So the pointers aren't really far pointers.
Something like:
#ifdef WIN32
#define FAR
#else
#define FAR _far
#endif
(or something like that).
Regards,
Rob Craig
Rapid Deployment Software
http://members.aol.com/FilesEu/
