Q145996: FIX: _setmaxstdio Causes Access Violation

Article: Q145996
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbCRT kbVC kbVC410fix
Last Modified: 30-JUL-2001

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The information in this article applies to:

- The C Run-Time (CRT), used with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 4.0, 4.1, 4.2 
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SYMPTOMS
========

The CRT function _setmaxstdio does not work properly. The function sets the
maximum number of files an application can open with the stream I/O functions,
like fopen. It is documented in the README book in the online documentation, and
in the Vcread.wri file.

Using _setmaxstdio results in the following error when you exit the program or
call the fopen function:

  Unhandled exception in <Project>.exe: 0xC0000005: Access Violation

RESOLUTION
==========

Do not use the _setmaxstdio function. Here are two workarounds:

- Keep track of the number of files opened with fopen, and do not open more
  than 512.

-or-

- If the application needs to open more than 512 files, use the low-level I/O
  functions: _open, _read, and _write. These allow up to 2048 files to be
  opened.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in Visual C++ 4.1.

MORE INFORMATION
================

Sample Code to Reproduce Problem
--------------------------------

  /* Compile options needed: none
  */ 

  #include <stdio.h>

  void main()
  {
      _setmaxstdio(511);
      FILE *text = fopen("textfile.txt","w");
      fclose(text);
  }

Additional query words: kbVC400bug 4.00 4.10

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Keywords          : kbCRT kbVC kbVC410fix 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

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