[Tutor] (no subject)

Alan Gauld alan.gauld at btinternet.com
Sat Oct 30 02:51:29 CEST 2010

"Steven D'Aprano" <steve at pearwood.info> wrote

> is actually being executed. There are very few programming tasks 
> harder than trying to debug code that doesn't actually contain any 
> bugs, or contains bugs different from the ones you are seeing, 
> because the code you are actually executing is something different 
> from what you think you are executing.

To illustrate with a true story (back in the days when you had to 
and maintain your own compilers!):

Take a C compiler source code and modify it so it produces faulty
executable code but does not crash or otherwise report an error.
Compile the now faulty compiler source code with the old (ie working)
Fix the source code bug.
Use the new (now broken) compiler to compile the now perfect source
code to produce a broken compiler with a slightly different defect.
Now use the resulting compiler to recompile the 'perfect' source code.
Now figure out why none of your executables work as expected.

That took us nearly 2 weeks to figure out... :-(
(And made us very thankful for source code version control!)

Alan G.

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