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From: ralf@b.gp.cs.cmu.edu (Ralf Brown)
Newsgroups: comp.sys.ibm.pc
Subject: Re: TC2.0 bugfree ?
Message-ID: <4075@pt.cs.cmu.edu>
Date: 20 Jan 89 18:11:37 GMT
References: <3785@druwy.ATT.COM>
Organization: Carnegie-Mellon University, CS/RI
Lines: 38

In article <3785@druwy.ATT.COM> rhm@druwy.UUCP (MasseyR) writes:
}No bugs in TC2.0 ?
}
}This small model C program :
}
}sub( cp )
}unsigned char 	*cp;
}{
}	int 	i;
}	i = (*cp++ << 8) + *cp++;
}}
}
}generates the following code fragment (I left out some of the .asm):
[fragment omitted]
}
}note that si (i.e. cp) is not incremented between references
}but instead after both references.

That is not a bug.  K&R explicitly state that the compiler may do the 
increment any time between the value's use and the next sequence point
(comma, end of statement, etc.).  You cannot rely on order-of-execution
within an expression, since the compiler is free to rearrange things as
it sees fit.  The code fragment 

	i = 4 ;
	printf("%d",i++ + i++ + i++) ;

has three legal results:
	12
	14
	15
depending on how many of the increments are deferred until after the 
additions.
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