We've been trying to get some backup code (which works fine on 32 bit
Sybase ASA 11) ported to work on the 64 bit database engine.

The original code was delphi, but we've ported it to C++ as faithfully
as possible, under VS2010 in x64 mode. DBToolsInit works fine and
gives no error. The code to invoke DBbackup is as follows:

#include "dbtools.h"

The callbacks are declared like this:

short __stdcall ErrorCallbackBackup (const char * str);
short __stdcall InfoCallback (const char * str);
short __stdcall ConfirmCallback (const char * str);
short __stdcall StatusCallback (const char * str);

The relevant struct is defined as follows:

a_backup_db g_backup_info;

the structure setup is as follows:

ZeroMemory (&g_backup_info, sizeof(g_backup_info));
g_backup_info.version = DB_TOOLS_VERSION_NUMBER;
g_backup_info.output_dir = g_szBackupDir;
g_backup_info.connectparms = g_szConnectStr;
g_backup_info.confirmrtn = ConfirmCallback;
g_backup_info.errorrtn = ErrorCallbackBackup;
g_backup_info.msgrtn = InfoCallback;
g_backup_info.statusrtn = StatusCallback;
g_backup_info.chkpt_log_type = BACKUP_CHKPT_LOG_DEFAULT;
g_backup_info.page_blocksize = 0;

g_backup_info.backup_database = 1;
g_backup_info.backup_logfile = 1;
g_backup_info.no_confirm = 1;

We invoke DBBackup like this

result = DBBackup(&g_backup_info);

We've also tried an explicit approach like this:

HINSTANCE hinst;
short (__stdcall * pdbbackup) (const a_backup_db *);

hinst = LoadLibrary (TEXT("dbtool11.dll"));
if (hinst != NULL)
{
pdbbackup = (short (__stdcall *) (const a_backup_db *)) GetProcAddress ((HMODULE)hinst, "DBBackup");
result = (*pdbbackup)(&g_backup_info);
FreeLibrary (hinst);

It made no difference...

Each callback is defined something like this

extern short __stdcall ErrorCallbackBackup (const char * str)
{
...
}

*** The structure packing is set to 1-byte ***

WIN64 and _WIN64 are defined, and we're point at the x64 LIB location
for Sybase (developer edition is installed).

EVERY SINGLE TIME we run this code, it fails with an access violation
in DBTOOL11.DLL

Can anybody shed any light on why this might be so?