Subj : Re: Non-strictly-conforming and unspecified versus undefined behavior
To   : comp.programming.threads
From : David Schwartz
Date : Thu Feb 17 2005 11:55 pm


    Let me say this one more time another way, because it's important. A 
program is strictly-conforming if it cannot be broken by changing it from 
one implementation of a standard to another. Any program that invokes 
undefined behavior is not strictly-conforming, because it can crash on one 
implementation and not on another (unless crashing is considered not to be 
broken). If a standard says you can do A or B and leaves which one 
unspecified, a strictly-conforming program must not work in the case of A 
and not work in the case of B.

    If a program had to perform identically, and produce identical output 
under all possible API implementations, it would be nearly impossible to 
write useful programs that strictly-conformed to POSIX. On the other hand, 
if you were allowed race conditions, strictly-conforming POSIX programs 
could break if you changed POSIX-compliant platforms.

    A program is strictly-conforming to a standard if it cannot be broken by 
any possible changes in unspecified behavior and does not invoke undefined 
behavior.

    DS

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