Dear i do not understand why the first example works and the second segfault. Thanks

----------------EXAMPLE 1 -------------------
// ldc2 -L=/usr/lib64/libXlib.so -L-lX11 -g -w xtest.d
import std.string;
import std.stdio;
import std.conv;
import std.c.stdlib : getenv;
import std.exception : Exception;

import X11.Xlib;

void main( string[] args ){
    Display* display = XOpenDisplay(getenv("DISPLAY"));
    if( display is null )
        new Exception( "Could not communicate with X server" );
    int counter;
    string pattern = "*\0";
    char** fonts   = XListFonts( display, pattern.dup.ptr, 10, &counter
);
    for(int c = 0; c < counter; c++)
        writeln( to!string( fonts[c] ) );
}


----------------EXAMPLE 2 -------------------
// ldc2 -L=/usr/lib64/libXlib.so -L-lX11 -g -w xtest.d
import std.string;
import std.stdio;
import std.conv;
import std.c.stdlib : getenv;
import std.exception : Exception;

import X11.Xlib;

void main( string[] args ){
    Display display = *XOpenDisplay(getenv("DISPLAY"));
    if( display is null )
        new Exception( "Could not communicate with X server" );
    int counter;
    string pattern = "*\0";
    char** fonts   = XListFonts( &display, pattern.dup.ptr, 10, &counter
);
    for(int c = 0; c < counter; c++)
        writeln( to!string( fonts[c] ) );
}

What's the definition of Display?

Le mardi 10 janvier 2012 à 01:26 +0100, Trass3r a écrit :
> What's the definition of Display?

This one:
_____________________________
struct _XDisplay{
    XExtData* ext_data;                             /* hook for
extension to hang data                              */
    _XPrivate* private1;
    int fd;                                         /* Network socket.
*/
    int private2;
    int proto_major_version;                        /* major version of
server's X protocol */
    int proto_minor_version;                        /* minor version of
servers X protocol */
    char* vendor;                                   /* vendor of the
server hardware */
    XID private3;
    XID private4;
    XID private5;
    int private6;
    XID function(_XDisplay*)resource_alloc;         /* allocator
function */
    int char_order;                                 /* screen char
order, LSBFirst, MSBFirst */
    int bitmap_unit;                                /* padding and data
requirements */
    int bitmap_pad;                                 /* padding
requirements on bitmaps */
    int bitmap_bit_order;                           /* LeastSignificant
or MostSignificant */
    int nformats;                                   /* number of pixmap
formats in list */
    ScreenFormat* pixmap_format;                    /* pixmap format
list */
    int private8;
    int release;                                    /* release of the
server */
    _XPrivate* private9, private10;
    int qlen;                                       /* Length of input
event queue */
    c_ulong  last_request_read;                     /* seq number of
last event read */
    c_ulong  request;                               /* sequence number
of last request. */
    XPointer private11;
    XPointer private12;
    XPointer private13;
    XPointer private14;
    uint max_request_size;                          /* maximum number 32
bit words in request*/
    _XrmHashBucketRec* db;
    int function( _XDisplay* )private15;
    char* display_name;                             /* "host:display"
string used on this connect*/
    int default_screen;                             /* default screen
for operations */
    int nscreens;                                   /* number of screens
on this server*/
    Screen* screens;                                /* pointer to list
of screens */
    c_ulong motion_buffer;                          /* size of motion
buffer */
    c_ulong private16;
    int min_keycode;                                /* minimum defined
keycode */
    int max_keycode;                                /* maximum defined
keycode */
    XPointer private17;
    XPointer private18;
    int private19;
    char* xdefaults;                                /* contents of
defaults from server */
    /* there is more to this structure, but it is private to Xlib */
}
alias _XDisplay Display;

It's likely a module Gmail - Problem with interfacing C code to D - Mozilla Firefo;

import std.algorithm;
import std.array;
import std.stdio;

void main()
{

}



On 1/10/12, bioinfornatics <bioinfornatics@fedoraproject.org> wrote:
> Le mardi 10 janvier 2012 à 01:26 +0100, Trass3r a écrit :
>> What's the definition of Display?
>
> This one:
> _____________________________
> struct _XDisplay{
>     XExtData* ext_data;                             /* hook for
> extension to hang data                              */
>     _XPrivate* private1;
>     int fd;                                         /* Network socket.
> */
>     int private2;
>     int proto_major_version;                        /* major version of
> server's X protocol */
>     int proto_minor_version;                        /* minor version of
> servers X protocol */
>     char* vendor;                                   /* vendor of the
> server hardware */
>     XID private3;
>     XID private4;
>     XID private5;
>     int private6;
>     XID function(_XDisplay*)resource_alloc;         /* allocator
> function */
>     int char_order;                                 /* screen char
> order, LSBFirst, MSBFirst */
>     int bitmap_unit;                                /* padding and data
> requirements */
>     int bitmap_pad;                                 /* padding
> requirements on bitmaps */
>     int bitmap_bit_order;                           /* LeastSignificant
> or MostSignificant */
>     int nformats;                                   /* number of pixmap
> formats in list */
>     ScreenFormat* pixmap_format;                    /* pixmap format
> list */
>     int private8;
>     int release;                                    /* release of the
> server */
>     _XPrivate* private9, private10;
>     int qlen;                                       /* Length of input
> event queue */
>     c_ulong  last_request_read;                     /* seq number of
> last event read */
>     c_ulong  request;                               /* sequence number
> of last request. */
>     XPointer private11;
>     XPointer private12;
>     XPointer private13;
>     XPointer private14;
>     uint max_request_size;                          /* maximum number 32
> bit words in request*/
>     _XrmHashBucketRec* db;
>     int function( _XDisplay* )private15;
>     char* display_name;                             /* "host:display"
> string used on this connect*/
>     int default_screen;                             /* default screen
> for operations */
>     int nscreens;                                   /* number of screens
> on this server*/
>     Screen* screens;                                /* pointer to list
> of screens */
>     c_ulong motion_buffer;                          /* size of motion
> buffer */
>     c_ulong private16;
>     int min_keycode;                                /* minimum defined
> keycode */
>     int max_keycode;                                /* maximum defined
> keycode */
>     XPointer private17;
>     XPointer private18;
>     int private19;
>     char* xdefaults;                                /* contents of
> defaults from server */
>     /* there is more to this structure, but it is private to Xlib */
> }
> alias _XDisplay Display;
>
>

Jesus christ, sorry about that my keyboard script went crazy and posted that.

What I was going to say is it's likely a mismatch of the struct sizes. In the second example you are dereferencing the pointer on the D size, which does a field-by-field copy of the pointed-to struct. But D will only read the exact amount of bytes that is defined by the structure. So if you end up reading e.g 176 bytes, but the C structure is actually more than that, then the C-side (X11) will end up reading into D memory past the 176th byte, and will segfault.

If you can, try seeing if you can get the size of the Display
structure in C code (e.g. use printf("%d", sizeof(Display))), and then
compare that to D with writeln(Display.sizeof). They must have the
same size.

On 01/10/12 01:02, bioinfornatics wrote:
> Dear i do not understand why the first example works and the second segfault. Thanks
> 
> ----------------EXAMPLE 1 -------------------
     Display* display = XOpenDisplay(getenv("DISPLAY"));

>     char** fonts   = XListFonts( display, pattern.dup.ptr, 10, &counter

> ----------------EXAMPLE 2 -------------------
>     Display display = *XOpenDisplay(getenv("DISPLAY"));

>     char** fonts   = XListFonts( &display, pattern.dup.ptr, 10, &counter

Do you expect the xlib functions to work with copies of private structures?

artur

Scratch that, in X11 apparently the Display structure is an incomplete type (so sizeof won't work). This means you most probably *have* to use pass it around as an opaque pointer. It's kind of odd because you can still access some of its fields (so it's not totally opaque), but you can't do copies.

So just use pointers and you'll be safe.

Hell I've never really done any C programming except what's in K&R, but this seems like a logical conclusion to me..