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From: ac@utgpu.UUCP
Newsgroups: comp.sys.m6809
Subject: C bugs
Message-ID: <1987May15.141952.4911@gpu.utcs.toronto.edu>
Date: Fri, 15-May-87 14:19:52 EDT
Article-I.D.: gpu.1987May15.141952.4911
Posted: Fri May 15 14:19:52 1987
Date-Received: Sat, 16-May-87 13:23:45 EDT
Organization: University of Toronto Computing Services
Lines: 38
Checksum: 55956

   I wasted quite a bit of time the last few days trying to port a
UUENCODE and UUDECODE program to OS9.  It was a port of a port of a port
but the version I finally got was for Mark William's C on an Atari ST.
The really aggravating aspect of my problems was that they resulted from
bugs I already knew about but I didn't think to check the source for
these problems when I started having difficulties.  Although these bugs
have been reported before, I will describe them again in the hopes that
others can avoid the problems I had.
1) Fopen normally opens the file specified in it's first argument according
to the access specified in it's second argument.  If the open fails for
any reason, then NULL is returned, otherwise a valid file pointer 
is returned.  If, however, the string which specifies the access includes
an invalid letter, then the open will always "succeed", and a non-NULL
file pointer is returned.  This file pointer is in no way associated with
the file you were trying to open!  It appears to be STDIN or STDOUT.
In my specific case the open was: fopen(argv[1],"rb")
"B" is not valid under OS9 C so when the program went to read from
my input file it hung waiting for input from the keyboard.
2) The code produced for comparisons of unsigned integers to literal zeros
is incorrect.  For example, if I is an unsigned int then the comparison
i>0 will not work correctly.  Code i!=0 instead.  Avoid "<", ">" and
combination of these with "=".
3) The final problem I had is one that I can't really put my finger on.
I had added a bunch of diagnostic fprintf functions calls to my program.
They were all very similar.  I had just copied them to various points
in the program to dump out the value of certain variables I was interested
in.  At one point I added a few more of these statements and started  
getting all sorts of "unresolved references" from the linker.
The solution seemed to be to remove some of the calls but I can't for the
life of me see how the last few added fprintf's were any different than
the earlier one.  Has anyone ever had any problems with unexplainable
unresolved references?
 
-- 

Name:     Mark Acfield (University of Toronto Computing Services)
Path:     ihnp4!utgpu!ac   
Alias:    ac@utoronto.bitnet