Q43219: scanf, sscanf, fscanf Functions Fail When Scanning All Zeros

Article: Q43219
Product(s): See article
Version(s): 2.00
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist2.00 | mspl13_c
Last Modified: 2-MAY-1989

The functions scanf, sscanf, and fscanf fail when all of the following
conditions are satisfied:

1. The format specifier for a field is any of the following, where "w"
   is the maximum input field width:

      %wX    %wI    %wD
      %wx    %wi    %wO
      %wlx   %wli   %wU

2. The field being scanned is all zeros and has a length of w.

3. The field being scanned is immediately followed by a valid digit
   (no intervening white space).

Under the above conditions, these functions read one extra digit from
the input buffer as if the "skip leading zeros" routine doesn't
realize that it is scanning past the maximum length specified (w).

To work around this problem, for the format specifiers %wD, %wO, and
%wU, use %wld, %wlo, and %wlu, respectively. For the remaining
specifiers, there is no workaround other than to scan the buffer
character by character.

Microsoft has confirmed this to be a problem in Version 2.00. We are
researching this problem and will post new information as it becomes
available.

The following program demonstrates this problem:

#include <stdio.h>

void main (void)
 { int a, b;

   /* There are 2 zeros, and w=2. */
   sscanf ( "0012", "%2x%d", &a, &b );

   /* This should output:   a=0 b=12
    * Instead, it outputs:  a=1 b=2
    */
   printf ( "a=%x b=%d\n", a, b );
 }

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