Q49006: DOS APPEND Is Not Utilized with access() Function

Article: Q49006
Product(s): See article
Version(s): 4.00 5.00 5.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | S_QuickC | mspl13_c
Last Modified: 16-JAN-1990

The Microsoft C run-time library function, access(), determines
whether or not a specified file exists and can be accessed in read
and/or write mode(s). The access() function searches the current
working directory for the particular file or the directory specified
by a path to the file.

The DOS APPEND command, which establishes a search path for data files
and works similarly to the PATH environment variable, appears to be a
way to assist access() in finding files outside the current working
directory without having to supply a path. However, the APPEND command
does not search the data path when locating a file to be used by the
access() function. Consequently, access() fails when searching for a
file issued with no path and that is not in the current working
directory.

As documented in the "Microsoft MS-DOS User's Guide and User's
Reference" on Page 30, APPEND searches the data path for all files
with only the following MS-DOS system calls:

   Code          Function
   ----          --------

   0FH           Open File (FCB)
   23H           Get (FCB) File Size
   3DH           Open Handle
   11H           FCB search first  (with /x switch only)
   4EH           Handle find first (with /x switch only)
   4BH           Exec (with /x switch only)

The access() function makes an MS-DOS system call to interrupt 21H
function 43H, which sets and retrieves file attributes. Since this is
not a system call listed above, APPEND does not perform file
searching.

The following program illustrates the APPEND limitation. The program
uses access() to determine whether the file named TEST exists. Assume
that the TEST data file is not in the current working directory, but
instead is in a directory called c:\foo, and that the APPEND command
"APPEND=c:\foo" was issued previously to set the appropriate search
path.

Sample Program
--------------

#include <io.h>
#include <fcntl.h>
#include <stdio.h>

FILE * stream;

void main( void )
{
  /* check for existence of TEST fails despite having APPEND set */
  if ((access( "TEST", 0 )) == -1 )
  {
        printf( "file was not found with APPEND set\n\n" );

  /* however, fopen() recognizes APPEND for successful access */
        if ((stream = fopen( "TEST", "r")) != NULL )
            printf( "file opened successfully using APPEND" );
  }
}

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.