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From: steve@jplgodo.UUCP (Steve Schlaifer x3171 156/224)
Newsgroups: net.lang.c,net.micro.att
Subject: Re: Why doesn't this work? (3B2 problem)
Message-ID: <746@jplgodo.UUCP>
Date: Fri, 21-Mar-86 12:55:32 EST
Article-I.D.: jplgodo.746
Posted: Fri Mar 21 12:55:32 1986
Date-Received: Sun, 23-Mar-86 11:20:23 EST
References: <276@birtch.UUCP>
Distribution: na
Organization: Jet Propulsion Labs, Pasadena, CA
Lines: 34
Xref: dcdwest net.lang.c:7162 net.micro.att:1021
Summary: are char's unsigned on 3B2?

In article <276@birtch.UUCP>, ken@birtch.UUCP (Ken B) writes:
> We have a 3B2/300, and I wrote this program to help debug our spooler problem
> (another story), why doesn't it work?  It never read's an EOF from stdin,
> and continues to dump 'nulls' to stdout.  
..................code deleted..........................
> 	char c;
> 
> 	c=getchar();
> 	if (c!=EOF)
............... remaining code deleted .................
> 
> This exact program works correctly on our Pyramid 90x, so I know its not just
> my program.

The getchar function is of type int; EOF is defined in stdio to have the value
-1.  When you say c=getchar(); and encounter an end of file, the value -1 from
getchar is converted to \377 when it is stored in c.  When c is later compared
to EOF, the value of c is converted to int and then the comparison is done.
This is all true no matter which machine you are running on.

I suspect the 3B2 uses unsigned char's and the Pyramid uses signed char's.
When \377 is converted to int on the 3B2, it becomes +127; on the Pyramid, it
becomes -1.  Obviously, +127 is not equal to -1 so c can never be equal to EOF
on the 3B2.  On the Pyramid, the sign extension done when a char is converted
into an int makes everything work out fine.  An easy fix for this type of
problem is to declare c as an int rather than a char.

-- 

...smeagol\			Steve Schlaifer
......wlbr->!jplgodo!steve	Advance Projects Group, Jet Propulsion Labs
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				Pasadena, California, 91109
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