From: Eric Backus <ericb AT lsid DOT hp DOT com>
Subject: Bug in strtoul(), and a fix
To: djgpp AT sun DOT soe DOT clarkson DOT edu (djgpp)
Date: Thu, 4 Jun 92 11:29:37 PDT
Mailer: Elm [revision: 66.25]

I have found a bug in strtoul().  The following program demonstrates
the bug:


#include <stdio.h>
#include <stdlib.h>

int
main(int argc, char **argv)
{
    char		string[10] = "0";
    char		*p;
    unsigned long	return_value;

    return_value = strtoul(string, &p, 0);
    if (return_value != 0)
	(void) printf("Conversion failed - returned %u\n",
		      return_value);
    if (p != &string[1])
	(void) printf("Pointer incorrect - offset %d from string\n",
		      p - &string[0]);

    return 0;
}


When compiled with djgpp 1.05, this program works correctly.  When
compiled with djgpp 1.06, the pointer "p" is not incremented to point
to string[1], but is instead left pointing to string[0].  Fortunately,
the return value (zero) is correct.

Strangely enough, the strtoul function found in libc.a works
correctly.  However, there is another strtoul function found in
libgcc.a, and gcc links -lgcc before -lc into the program, so this
other copy of strtoul is the one that gets used.  And this other
strtoul, found in libgcc.a, is the one with the bug.

To fix this bug, we could probably remove strtoul from libgcc.a.  This
seems like the cleanest fix if it works (and I suspect that it does
work), but I don't understand the purpose of libgcc.a well enough to
know if this would break anything.

An alternative is to fix the strtoul found in libgcc.a to work
correctly.  I decided to do that.  The problem is that the zero
character in the string is interpreted as meaning "the following
number is octal", and then since there are no other characters,
strtoul decides that the conversion failed.  Following is a patch to
strtoul.cc found in /djgpp/libsrc/gcc, that fixes the problem:


*** strtoul.cc.ori	Thu Jun  4 10:55:09 1992
--- strtoul.cc	Thu Jun  4 10:56:48 1992
***************
*** 54,59 ****
--- 54,61 ----
  	      s++;
  	      base = 16;
  	    }
+ 	  else
+ 	      s--;	/* Undo s++ since leading '0' is also a valid digit */
  	}
      }
  

--
				Eric Backus
				ericb%hplsla AT hplabs DOT hp DOT com
				(206) 335-2495