From: jameskuyper@alumni.caltech.edu   
      
   On 2025-11-01 17:39, Tristan Wibberley wrote:   
   > Follow-up set comp.lang.c   
   >   
   > On 01/11/2025 02:45, Richard Damon wrote:   
   >   
   >> .. [stuff I think is about the invalidity of not completing execution]   
   isn't a valid definition ...   
   >   
   > Let's suppose C disallows abort due to external events... Then no   
   > conforming C implementation exists.   
   >   
   > I think we must suppose that susceptibility to power-cuts do not render   
   > C implementations non-conforming.   
      
   Correct. What a power cut does is make a conforming implementation of C   
   fail to continue qualifying as a implementation.   
      
   In 1.6 of C89, an implementation is defined as "a particular set of   
   software, running in a particular translation environment under   
   particular control options, that performs translation of programs for,   
   and supports execution of functions in, a particular execution environment."   
      
   Thus, when the power is cut, the software ceases to run, so it ceases to   
   be an implementation, and in particular, ceases to be a conforming   
   implementation.   
      
   There's important wording that wasn't added to the standard until C99   
   that clarified something that was already considered to be true: "A   
   program that is correct in all other aspects, operating on correct data,   
   containing unspecified behavior shall be a correct program and act in   
   accordance with 5.1.2.3." (4p3). The peculiar wording is intended to   
   make clear that unspecified behavior does not relieve an implementation   
   of this requirement.   
   Section 5.1.2.3 indirectly references most of the rest of the standard,   
   while defining that only the observable behavior of a program has to   
   match what the standard says - that behavior doesn't have to be   
   generated in the fashion that the standard describes. Section 5.1.2.3 in   
   C99 corresponds to 2.1.2.3 in C89.   
      
   The rest of the standard defines, among other things, how a program   
   exits. If the behavior of the program is not undefined, it can only exit   
   by reaching the end of the main() function, or by calling certain   
   library functions. If there is any observable behavior that allows you   
   determine that it ended by any other method, the implementation is   
   non-conforming.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)