TCHAR access in Windows structures ...

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shutdownall

Joined: 02 Apr 2010
Posts: 517
Location: Munich

shutdownall 23 May 2012, 15:51

Sorry, need some help, fighting with Windows and following structure;

typedef struct _DEV_BROADCAST_PORT {
DWORD dbcp_size;
DWORD dbcp_devicetype;
DWORD dbcp_reserved;
TCHAR dbcp_name[1];
} DEV_BROADCAST_PORT, *PDEV_BROADCAST_PORT;

http://msdn.microsoft.com/en-us/library/windows/desktop/aa363248%28v=vs.85%29.aspx

How can I access dbcp_name (show the name in a message box) ?

Quote:

dbcp_name

A pointer to a null-terminated string specifying the friendly name of the port or the device connected to the port. Friendly names are intended to help the user quickly and accurately identify the device—for example, "COM1" and "Standard 28800 bps Modem" are considered friendly names.

Tried to define this way:

Code:

struct DEV_BROADCAST_PORT
  dbcp_size             dd ?
  dbcp_devicetype       dd ?
  dbcp_reserved         dd ?
  dbcp_name             dd ?
ends   

        mov     ebx,[lparam]
        virtual at ebx
        dbp     DEV_BROADCAST_PORT
        end     virtual
        invoke  MessageBox,[hwnd],[dbp.dbcp_name],_caption,MB_ICONERROR+MB_OK

But this kills my application.
Other "definitions" I tried are not accepted by FASM.

One additional hint:

Quote:

dbcp_name is not a pointer
The dbcp_name member is not a pointer. This is a variable-length structure, and dbcp_name is an array that contains the actual characters of the port name.

So this seems to be an error in the documentation.

Thanks. Wink

23 May 2012, 15:51

AsmGuru62

Joined: 28 Jan 2004
Posts: 1671
Location: Toronto, Canada

AsmGuru62 23 May 2012, 16:02

Maybe this way:

Code:

        mov     ebx,[lparam] 
        lea      eax, [ebx + DEV_BROADCAST_PORT.dbcp_name] 
        invoke  MessageBox,[hwnd],eax,_caption,MB_ICONERROR+MB_OK

23 May 2012, 16:02

shutdownall

Joined: 02 Apr 2010
Posts: 517
Location: Munich

shutdownall 23 May 2012, 17:33

Thanks AsmGuru,

the following worked:

Code:

struct DEV_BROADCAST_PORT
  dbcp_size             dd ?
  dbcp_devicetype       dd ?
  dbcp_reserved         dd ?
  dbcp_name             db ?
ends

        mov     eax,[lparam]    ; pointer to DEV_BROADCAST_PORT structure
        add     eax,12
        invoke  MessageBox,[hwnd],eax,_caption,MB_ICONERROR+MB_OK

Is strange that the pointer is not accessible.
dbcp_name is the first character of a null terminated string.
Sometimes you can get nuts what's going on in the brain of Microsoft developers. Rolling Eyes

By the way in my case it is representing a 4 character string ( "COM4" ).

23 May 2012, 17:33

AsmGuru62

Joined: 28 Jan 2004
Posts: 1671
Location: Toronto, Canada

AsmGuru62 23 May 2012, 21:11

DEV_BROADCAST_PORT.dbcp_name is actually at offset of 12 bytes, so it should have worked too.

23 May 2012, 21:11

shutdownall

Joined: 02 Apr 2010
Posts: 517
Location: Munich

shutdownall 23 May 2012, 21:35

Yes I know, don't like to use lea when I can use add instead.
Anyway strange syntax to use a structure for non structured data (variable length of structure content).

23 May 2012, 21:35

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