Solved

Calling fopen in DLL called from VB?

Posted on 1997-05-23
2
829 Views
Last Modified: 2013-12-03
We've written a 16 bit DLL in C++ that opens file using the MFC CStdioFile and CFile classes.  These use the fopen C
runtime library function and the _dos_open library
function respectively.

The problem is that when this DLL is called from an Access
Basic (V2)application or a VB (V4) application that has an
Access database open, the opens of CStdioFile
objects sometimes fail.  The m_cause member of
the associated CFileException object returns a 1
(generic) and the m_lOsError member contains 0.

The problem does not occur when called from a non-Access
VB application or from applications written in C++ (no
Access).

At the time of the failure, the DLL has only one other
file open (CStdioFile) and is trying to open another
CStdioFile.

The problem occurs in both Windows 3.x and Win95.

I found one short and unresolved thread on what sounded
like the same problem. One contributor pointed to a MSDN
article entitled "Creating Custom Add-in Libraries for
Word 6.0 Using the Word API."  This article suggests that
using text mode DOS file handles is not guaranteed to work
in a DLL called from Word.  The author of the referencing
newsgroup message suggested that this may be true for
VB and Access Basic as well.  While this might explain
the behaviour, I am skeptical.

Thanks.
0
Comment
Question by:NickDanger
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
2 Comments
 

Accepted Solution

by:
ajh020797 earned 200 total points
ID: 1397624
If the problem is purely with text files, why fopen with the binary flag set and remember to put \r\n instead of \n ?
0
 

Author Comment

by:NickDanger
ID: 1397625
Thanks ajh!
I was looking for an explanation however.  I've since been
able to "fix" the problem, by increasing the file handle
count in my DLL (ala MSDN article "Increasing File Handles"
found in section 2.7 of the Runtime Library Reference).

While this seems to have fixed the problem, I am still troubled
since I cannot explain it.

Thanks again.

0

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

This tutorial is about how to put some of your C++ program's functionality into a standard DLL, and how to make working with the EXE and the DLL simple and seamless.   We'll be using Microsoft Visual Studio 2008 and we will cut out the noise; that i…
This article describes how to programmatically preset the "Pages per Sheet" option that's available with most printer drivers.   This setting lets you do "n-Up" printing, where two, four, or more pages are printed on each sheet of paper. If your …
This is Part 3 in a 3-part series on Experts Exchange to discuss error handling in VBA code written for Excel. Part 1 of this series discussed basic error handling code using VBA. http://www.experts-exchange.com/videos/1478/Excel-Error-Handlin…
This video shows how to use Hyena, from SystemTools Software, to update 100 user accounts from an external text file. View in 1080p for best video quality.

734 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question