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ctypes NULL pointers; was: Python To Send Emails Via Outlook Express

Posted in a previous thread was some Python code for accessing Window's
Simple MAPI api using the ctypes module.


This Simple MAPI module was Ian's completed version of an example
I had posted in an earlier message. In it I had to set some pointer
fields in a C structure to NULL. I was not happy with the solution I
used so I made an inquiry on the ctypes-users mailing list. Thanks to
Thomas Heller I got some answers.

The simplest way to create a NULL pointer instance in ctypes is to
call the pointer class without an argument.

from ctypes import POINTER, c_int
INT_P = POINTER(c_int) # A pointer to a C integer
p = INT_P() # An INT_P instance set to NULL

When the pointer is a member of a structure things are a little different.
For the ctypes primatives c_void_p, c_char_p and c_wchar_p one can simply
use None to set the field NULL.

from ctypes import Structure, c_void_p
class STRUCT(Structure):
_fields_ = [('voidptr', c_void_p)]
s=STRUCT( None ) # Create an instance with voidptr field NULL

This is documented in the ctypes tutorial. A problem with ctypes 0.9.2
prevents using None to initialize POINTER derived fields. This has
been fixed so future releases will allow it. In the meantime the
following will work.

class IPSTRUCT(Structure):
_fields_ [('intptr'), INT_P]

A null pointer of the correct type is assigned to the field. I hope this
clears up any confusion my Simple MAPI example may have caused regarding
ctypes pointers.

Lenard Lindstrom
Jul 18 '05 #1
3 5016
Thanks again Lenard!!

Jul 18 '05 #2
Hi Lenard
Hopefully I have understood you properly.
The updated script is now as follows, or you can download it from
Thanks again for all your help!!!

Kindest regards
Ian Cook
import os
from ctypes import *

FLAGS = c_ulong
LHANDLE = c_ulong
# Return codes
# Recipient class
class STRUCT(Structure):
_fields_ = [('voidptr', c_void_p)]
#NULL = c_void_p(None)
NULL=STRUCT( None ) # Create an instance with voidptr field NULL

class MapiRecipDesc(Structure):
_fields_ = [('ulReserved', c_ulong),
('ulRecipClass', c_ulong),
('lpszName', c_char_p),
('lpszAddress', c_char_p),
('ulEIDSize', c_ulong),
('lpEntryID', c_void_p),
lpMapiRecipDesc = POINTER(MapiRecipDesc)
class MapiFileDesc(Structure):
_fields_ = [('ulReserved', c_ulong),
('flFlags', c_ulong),
('nPosition', c_ulong),
('lpszPathName', c_char_p),
('lpszFileName', c_char_p),
('lpFileType', c_void_p),
lpMapiFileDesc = POINTER(MapiFileDesc)
class MapiMessage(Structure):
_fields_ = [('ulReserved', c_ulong),
('lpszSubject', c_char_p),
('lpszNoteText', c_char_p),
('lpszMessageType', c_char_p),
('lpszDateReceived', c_char_p),
('lpszConversationID', c_char_p),
('flFlags', FLAGS),
('lpOriginator', lpMapiRecipDesc), # ignored?
('nRecipCount', c_ulong),
('lpRecips', lpMapiRecipDesc),
('nFileCount', c_ulong),
('lpFiles', lpMapiFileDesc),
lpMapiMessage = POINTER(MapiMessage)
MAPI = windll.mapi32
MAPISendMail.restype = c_ulong # Error code
MAPISendMail.argtypes = (LHANDLE, # lhSession
c_ulong, # ulUIParam
lpMapiMessage, # lpMessage
FLAGS, # lpFlags
c_ulong, # ulReserved
def SendMail(recipient, subject, body, attachfiles):
"""Post an e-mail message using Simple MAPI
Special thanks to Lenard Lindstrom!

recipient - string: address to send to (multiple address sperated
with a semicolin)
subject - string: subject header
body - string: message text
attach - string: files to attach (multiple attachments sperated
with a semicolin)

Example usage
import simplemapi

simplemapi.SendMail("to********@server.com;to***** ***@server.com","My
Subject","My message body","c:\attachment1.txt;c:\attchment2")

# get list of file attachments
attach = []
AttachWork = attachfiles.split(';')

#verify the attachment file exists
for file in AttachWork:
if os.path.exists(file):
attach = map( os.path.abspath, attach )
nFileCount = len(attach)

if attach:
MapiFileDesc_A = MapiFileDesc * len(attach)
fda = MapiFileDesc_A()
for fd, fa in zip(fda, attach):
fd.ulReserved = 0
fd.flFlags = 0
fd.nPosition = -1
fd.lpszPathName = fa
fd.lpszFileName = None
fd.lpFileType = None
lpFiles = fda
# No attachments
lpFiles = cast(NULL, lpMapiFileDesc) # Make NULL

# Get the number of recipients
RecipWork = recipient.split(';')
RecipCnt = len(RecipWork)

# Formulate the recipients
MapiRecipDesc_A = MapiRecipDesc * len(RecipWork)
rda = MapiRecipDesc_A()
for rd, ra in zip(rda, RecipWork):
rd.ulReserved = 0
rd.ulRecipClass = MAPI_TO
rd.lpszName = None
rd.lpszAddress = ra
rd.ulEIDSize = 0
rd.lpEntryID = None
recip = rda

# send the message
msg = MapiMessage(0, subject, body, None, None, None, 0,
cast(NULL, lpMapiRecipDesc), RecipCnt, recip,
nFileCount, lpFiles)
rc = MAPISendMail(0, 0, byref(msg), 0, 0)
raise WindowsError, "MAPI error %i" % rc


Jul 18 '05 #4

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